Climatological Bulletin Vol. 21, No. I , February/Fe.rier, 1987

Bulletin climatologique

Canadian Meteorological and Oceanographic Society

La Societe Canadienne de Meteorologie et d' Oceanographie

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Climatological Bulletin Bulletin climatologique Vol. 21, No. I, February/Fevrier, 1987

2 FOREWORD / AVANT·PROPOS

ARTIC LES

3 The Spatial Distribution of Heavy Precipitation in the Greater Victoria Region S.E. Tuller

19 Synoptic Weather Conditions During the Porter Lake Experimental Fire Project M.D. Flannigan and J.B. Harrington

NOTES

41 Summary and Highlights of the 1984 Severe Local Storm Season M.J. Newark, M. Leduc, L. Legal, F Letchford, S. Siok, A. Wallace, and D. Waugh

NEWS AND COMMENTS / NOUVELLES ET COM MENTAIRES

52 Alberta Climatological Association Annual Meeting 52 Climate Change Information

Henry Hengeveld 53 Saskatchewan Climate Advisory Committee

Ken Jones 53 ACFAS Annual Conference

ISSN 0541-6256

Editor / Redacteur en chef: S.J. Cohen Associate Editors / Redacteurs associes: T.R. Allsopp A. Hufty B.L. Magill S. Tabata R.B.B. Dickison J.R.N. Lazier G.R. McBoyle E.E. Wheaton

Foreword / Avant-Propos

This issue includes a note o n the 1984 severe IOClil storm season by M.J . Newark et 01. The referees felt that this type o f review should be published o n an annual basis as a feature item in News and Comments. Hopefully, the Bulletin will he able to olTer these reviews regularly, weather permitting.

In the October 1986 issue, r noted tbe decision by CMOS Council to institute voluntary page charges for research articles and nOles. The NSERC grant still has 2 nlorc years to rlln, but there are no gliarantees ofsuppOrl beyond 1989, The page charges should eliminate most of our operating deficit fo r now, and as the Bulletin continues to grow, additional subscriptions will ensure financial viability over the lo ng term.

As we look to the fU lure, it gives me great pleasure to announce the appointment of Terry Allsopp and Bonnie Magill to the Board as Associate Editors. Their nominations were approved at CMOS Council Meeting No.2, held September 8, 1986.

Stewart 1. Cohen

2 Climatological Bulletin / Bulletin climatologiquc 21(1) 1987

The Spatial Distribution of Heavy Precipitation in the Greater Victoria Region

Sllm lOfI E. Ttllfer Departmenl of Geography University of Victoria Box 1700, Victoria, B.C. V8W 2Y2 LOriginal man LL'iCript received 7 March 1986; in revised fo rm 27 May 1986]

ABSTRACT

The dist ribution of precipitat ion during heavy minfall events is an important and

practical aspect of the prccipilation cl imatology of an area. The mapping of the spalial

d istribut ion of total stornl p recipitation revealed two basic distribution patterns of

hc:lVy precipitation in the Greater Victoria region. The first pattern, characteris tic of

storms of moderate in tensify, resem bled that of annua l total precipitation. T he second,

no t before described in discussions of the precipitation pallcrns in the Greater Victoria region and associated with some of the most intense storms, had high precipitation

totals in the usually drier southeastern part of the region, and low totals in the re lat ively

wel north. A prel iminary analysis ind icated that direction of upper air wind flow was

best able to di stingui~h between the two dis tribution patterns. The first pattern oecurrt d

duri ng flow from the southwest quadrant , whereas the less frequent, sewnd pallern was associated with winds from the no rthwest quadrant.

RilsUMil

La pluviometrie est un aspect important de la climatologic meteorologique d'une

regiOlL l e releve! earlographique des precipitalions tolll ies d'orllge revclent deu~

modelcs pluviometriqu e.~ fondarnenlaux dans Ie grand Victoria metropolitain. le

premier modele qui es t C",ua(;leristique des mages de moycnnc intensite, ressemble Ii. la

p recipitation annuelle totalc. Lc ~econd mod!!:le, jamais deerit auparavant pour discuter Ie mode de precipi tations affectant Ie gmnd Victoria mttropoJitain etl it a quelques­

unes des plus vio lentes onlges, indique des taux de pn!cipitations eleves dans la region

sud-cst habitueJlcment seehe, ct peu eleves au nord dans la region humide. l'analyse

preliminai re Iivele que la direction des ma.~ses d'ai r a haute al tit ude est Ie mieux a mcme de distingucr ent re les deux modeJes. Le premier modele survient durant des courants iltmospheriques venant du sud-ouest, quant a u second modele, moins

freq uent, est associe aux vents du nord-ouest.

Climatological Bulletin / Bulletin cl imalOlogiquc 2 1(1 ) 1987 C Canadian Meteorological and Oceanographic So

I. INTRODUCTION

A knowledge of Ihe spalia l distribution of precipitation during heavy rainfall ~vents is important in many aspects of applied climatology and hydrology. The design of Slormwater drainage systems, assessmenl of erosion potential and the evaluation of Ilood risk and Ilood control strategieoo are just a few common, practical examples. T he distribution of mean annual precipitation over most populated arcas is reasonably well known. The distribution of heavy precipitation from individual severe stomlS can be 4uit~ variable, however. This is especially true of convective slorms. Even the long term, climatic pattern of heavy precipitation can differ from lhat of mean annual precipitation. Thus, it i .~ often necessary to make an independent assessment of its distribution and not rely on the bctler known distribution of total precipitation.

The purpose of the present study is to present the pattern of precipitation during heavy rainfall events in the G reater Victoria, British Columbia, region; and to see how this paltern relates to that of mean annual precipitation. Most precipitation in Victoria is produced by mid-latitude cyclonic storms. This combined with lhe dominant influence of orographic controls should produce a more consistent distribution of storm precipitation than that found in areas of low rel id where small size, convective storms an: responsible fo r most oftb e heavy rainfall events. The relief features, both local relief and nearby hilts and mountain ranges, also produce a marked variation in precipitation across the region. This makes the Greater Victoria area an interesting laboratory in which to investiga te lhc spat ial variations in storm precipitation. Although the emphasis in the present study is on the spatial variation, some possible reasons for different distribution patterns arc suggested.

2. METHODOLOG Y

The term "heavy" precipitation event, as used in Ihis study, refers to a storm in which 40 or more mm of total precipitation was recorded during one climatological day at either of the two principal climatological stations in Ihe Grealer Victoria rcgion: Victoria Gonzales Heights or Victoria International Airport. The term ;'rainfall" is used synonomously witb "precipitation" because most of the heavy precipitation in Victoria falls as rain. These storms arc subdivided into two c."tegories. Storms of "moderate intensity" are defined as those that produce between 40 and 60 mm of tOlal precipitation per day. "I ntensc" storms produce over 60 mm.

The Greater Victoria region considered ht:f"e is similar 10 that included by the Atmospheric Environment Service in its Monthly

Meteurological SWI/I1/UfY ror the area. It includes metropolitan Victoria (the municipalities or Victoria, Oak Bay, Esquimalt and Saanich): and the rural-

• Climatological Bulletin I Bu llet ln climatologique 21(1) 1987

•

Inlet

• VICTORIA· HIGHLAND

.'~-J

I I I I • I I I I

•

• D

• Haro

.~ .. Strait

• f' -- - '1.- r I I

• 'I I

VICTORIA· GORDON HEAD

VICTORIA· GONZALES

HEIGHTS

~ N

I

Juan • S'.UOfI .... d I" ' ''10 " .. dy

de Fuca

Slra i l

FIG URE l. Map of the Greater Victoria region and ~taliomi llScd in this study.

suburban areas extending northward through the Saanich Peninsula and westward to the foothills of the hills and mountains of central Vancouver Island (Figure I). A tOlal of 27 stations which had data for sullieienl storms arc included in the analysis.

S.£. Tlliler / Spatial Distribution of Heavy Precipitation ill Vicloria 5

Heavy precipitation events which occu rred during the 1968 to 1984 period were selected on the basis of high one-day totals at Victoria Gonzales Heights and Victoria International Airport. Maps uf th e distribu tion patterns were prepared based on IS events or storms. Two additionul storms were included for the examination of possible controls of the differenl distribution patterns.

One-day precipitation totals were used in this study because this is the minimum time unit available at most of the stations in the area. Although the intensity over shorter time intervals might be of more interest for design purposc.<; and ot her applications, recording rain gauge dat~l. were available for only two to four stations depending on the storm, This number was not adequate for the present study which is interested in the distribution of precipitation throughout the region.

The one-day rainfall totals arc measured usi ng standard procedures and the standard rain gauge at all stmions. Duri ng the time period covered by this study the older, copPer, Type A gauge was being replaced by the larger. plastic, Type B gauge. Allhough there is no uniformity in Iype of gauge employed at all stations during the more recent storms Ihe type of gauge should not be a factor in dill"erent recorded rainfall amounts.

Victoria Gonzah.'S Heights and Vil,.1oria internat ional Airport each have a Nipher snow gauge. None of the siorms analysed in this study produced only snow with no rain. Total precipitation in storms with a mixture of snow and rain is measu red with the rain gauge at all stalions when snowfall is light enough Lhat it does nOI plug or overflow the gauge. The amount of water produced by rain and melted snow io the snow gauge i.s recorded as the total precipitation al the two principal climatological stations in storms when the rain gauge does not adequately handle the snow. Thus, some difference in results could occur in storms with heavy snowfall. Snow was reported in four of tht: 18 storm~ analysed here but in only one did it represent an important addition to total precipitation.

The IOta l precipitation recorded during the storm event rather than thai for the day of heaviest precipil"ation was used to overcome the problem of different observation times. Prior to January I, 1982, the climatological day ran from 10:00 p.m. to [0:00 p.m. Pacific Standard Time at both Victoria International Airport and Victoria Gonzales Heights, and fro m 8:00 a.m. 10 8:00 a.m. at most other stations in the area. Gonzales Heights has been using a 10:00 a.m. 10 10:00 a.m. period since January I. 1982. Thus, the same amount of precipitation fall ing at the same limc. .. could show up as dilTerent daily lotals because of the 10 to 12 hour deviation ill observation time among stations. Although the precipitation evenls were selected on the basis of high one-day tOlals the actual analysis included the bulk of the precipitation credited to adjacent days as well.

Recording rain gauge data were used to verify that the ranki ng of available stalions in terms of total storm precipitation was similar to the

6 Climatological Bulletin / Bulletin climatologiquc 21 (1 ) 1987

ranking in terms of shorter duration precipitat ion. The ratio of storm precipitation at a particular station to that at

Victoria Gonzales Heights is used to illustrate the variation of storm precipitation. The relative rather that the absolute variat ions are highlighted. Gonza les Heights was selet-1ed as the reference station because it has the. longest continuous record of any station within the study area and is the station whose data have mosl often been quoted in studies describing the climate of "Victoria."

An initial inspection of the data revealed thai two distinct pallerns Of storm precipitation existed in the Greater Vi(.toria region. One, composed primarily of storms of moderate intensity, showed higher amounts at Victoria I nternational Airport and the northeru part of the st udy area than a t Victoria Gonzales Heights and the Oak Bay area. Gonzales Heights and the southeast had higher totals during many especially heavy precipitation events, however. Each of these two cases had its own unique precipitation distribution pattern. Each case was mapped separately in order to present a comprehensive picture of the distribution of heavy precipitation. Nine storm$ werc included in each group. A composite map was also constructed to portray the over'JU pattern of heavy precipitation in the Greater Victoria area. Ten of the original 18 storms were selected for this map based on the data recorded at two stations with complete records located nt:ar the centre of the region (Victoria Highland and Victoria Gordon Head). T he qne-day precipitation totals at these stations were added together and the ten storms wit h thc largcst totals were sele<:ted. These rtre the storms that brought the most precipitation to the centre of the Greater Victoria region irrespective of the relative difference between the north and southeastern sections.

The median ratio of storm precipitation at a particular statio11 to thai at Gom:aks Heights is reported. The usc oftht median rather than the mean reduces the dIect of extreme values and in most cases .prod uces a conservative estimate orthe deviation of precipitation from that at Gonzales Heights. The median rat ios are given as dot symbols for eaeh station. This el iminates the errors inherent in drawing isolilles through an area where a great deal of local variation can exist and avoids giving an impression of accuracy that is unwarranted by tbe available station density. In the rare cases where the median Jatio was on tbe boundary between two classes, the mean and the distribution of values were used to determine whether the station belonged in the higher or lower category.

Although the precise pattern of predpitation in the Greater Victoria region will vary from storm to storm and the mapped patterns will depend on the particular cases included, the maps presented in this study should be indicative of the expected regional pattern of heavy precipitation.

Selected surface and upper air data and eharacterist i~ of each storm were stored in a microcomputer. A database management system was used to select those factors Ihat either singly or in combination correctly

S.E. 71/ller / Spalial Distribution of Heavy Precipitatiol/ in Victoria 7

differentiated the storms in which Victoria Gonzales Heights had the higher precipitation total from those in which Victoria International Airport received more. Although this does nOI prove cause and effect. it docs indicate the conditions which were closely associated with one distribution pattern versus the other.

Surface wind direction, wind speed, fo rm of precipitation and relative humidity at both Gonzales Heights and the Airport were taken from the Monthly Meleoroiogical Summmy for the Grellfer Victoria Region. Approximate surface vapour pressure was determined from the relative humidity and air temperature. The storm track and front Iype wcre obtained from the 120() GMT (0400 PST) surface analysis weather maps drawn by Pacific Weather Centre in Vancouver and the 1200 GMT maps published in NOAA's Daily Weather Map.t This latter source also provided the 1200 GMT 500 mb wind direction.

The distribution of 1951-1980 normal, annuallOtal precipitation was mapped using the data published by the Atmospheric Environment Service ( 1982). The isohyets, al an interval of 100 mOl , were interpolated with the aid of the patterns presented by Chilton (1973) and Coligado (1980).

3. RES ULTS

Distribution a/Mean Annllal Pfecipilatiall Tbe mean annual total precipitation increases from east to west across the Greater Victoria region (Figure 2). The western portion ofl he region is closer to the axis of the hills of central Vancouver Island and receivcs more orographic spillover of precipitation. The subsidence of air and the "rain· shadow" effeet of the mountains become beller established in the eastern parts of the region. The northern portion of the region is closer to the mountains than is the southern part at the same longitude and also is less protected by the effects of the Olympic MountainS located approximately SO km to the so uthwest. The protect.ion of the Olympics for the southern part of the region is maximized with a southwesterly air flow pattern. This is the direction of wann, moist, middle level air flow that accompanies much of the winter precipitation (Walker, 1961). The principal track of winter low pressure systems also approaches southern VanCOuver Island from the southwest (K lein, 1957). Thus, there is a tendency toward more precipitation in the north although thi~ is often overwhelmed by the east-west gradient and the effects of local relief (Figure 2).

Local rdie[ exerts an effect that is superimposed on the east-west gradient. Higher areas like that surrounding the Victoria Highland stalion experience greater precipitation than do other areas. There are probably minor local differences created by smaller relief features but the stlltion density is not adequate to fully document their extent or magnitude.

R Climatological Bulletin / Bulletin clirnatologique 21(1) 1987

~ N

I

FIGURE 2. Genernljtcd dislribululIl of 195 1-1980 normal rn!;an .. nnLla! total prccipilallon (mm).

Di.~lriblllioll of IleallY Precipitation Heavy precipitation in the ViclOria area is brought about by winter, mid­latitude cyclonic storms. December is the month with the greatest frcquency of heavy precipitation events. This pattern differs from thaI in much of the rest of

S.E. Tuller I Spatial Distribll/iQ11 of Heavy Precipilalioll in ViclOrio 9

Southern Canada. Convective precipitation that often brings brief but intense downpours 10 many other parts of the country during the summer is not often a factor in Victoria. Victoria can receive moderate convective precipitation in unstable air following fronts in the spring. The one-day totals arc usually much tess than those brought by severe, mid-winter cyclonic storms; however. The expected magnitude of very short duration rainfall is rdatively low in Victoria (National Re.~earch Council of Canada, 1975). One-day precipitation totals are comparable but often the season and responsible storm systems differ, Stations in eastern Canada onen receive their highest one-day totals from tropical cyclones which affect the area in summer or early fa ll rather than mid-winter. High ontXiay Wlals on the Prairies also occur in summer when fro ntal systems can trigger uplift in moist, unstable air. The Victoria area in the rain shadow o[ Vancouver Islam.J and the Olympic Mountains, receivcs much less heavy precipitation than do more exposed stations on the west coast of British Columbia. Overall, the Greater Victoria area has a comparatively benign heavy preci pitation regime.

The distribution of heavy precipitation does not lIsually mirror the distribu tion of mean annual precipitation. Even in an area such as Victoria where because of orographic effects we might expect a closer coincidence, the two patterns quite often do not ,-,gree. The distribution during ni ne events that include some of the highest one-day precipitation totals recorded in the Victoria urea showed more precipitation at Gonzales Heights and the southeast of the region tha n was recorded in the northern Saanich Peninsula in the vicin ity of the Airport (Figure 3.) One-day precipitation totals recorded at Gonzales Heights ranged from 40.1 mm to 83.3 mm in this sample. The median was 61.0 mill.

The general east to west increase in precipitation still prevailed in the distribution pattern of these storms (Figure 3). Downtown Victoria received about 20 percent more precipitation than did Gonzalt-s Heights. Thl! higher elevation Victoria Highland stat ion and lhe Metchosin area, located closer to the mountains in the southwest, received over 35 percent more.

The distinctive feature of this heavy storm precipitation pallero was the low values in the central and northern Saanich PeninSula, a region thal usually receives relatively high precipitation. The locus of lowest precipitation in the Greater Victoria region has shifted from the southeast (Oak Bay) to the north (North Saanich). T he mediall mtio of precipitation at Victoria International Airport to that at Victoria Gonzales Heights was only 0.79.

One basic difference in the precipitation pattern.~ seems to be in the intensity of precipitation. Victoria International Airport gets ntore total precipitation and much more moderate imensity rainfall. It receives 35 percent more mean annual total precipitation (873 mm compared wit h 647 mm at Gonzales Heights; Atmospheric Environment Se.rvice, 1982). The average highest one-day and 24-hour precipitation totals in the year arc also higher at the Airport (45.1 mID and 51.911\111 respectively) than at Gonzales Heights

III Climatological Bulletin / Bulletin climatologique 21(1) 1987

•

Saanich

• VICTORIA· HIGHLAND

VICTORIA '" o INTERNATIONAL AIRPORT

~~ I I I

'0@ : 0 I I I

Saanich

Haro

Strait

VICTORIA· GORDON HEAD

~ N

I

o ' " VICTORIA· GONZALES

HEIGHTS

Juan

CD .S&-.!IIi

([D .96-\ O!i

0 106'1 15

<J) 116·125

~ 1.26·\J5 de Fuca

S tra ll . "" f' IGURE J . Median ralio of sta tion 10 Viclo ri~ Gonzales l leigh[s precipi['i1 ion ror stMmS when Gonz.alcs lleighls recorded more precipitation Ih~n Vit;lOria Inlernal ional Airport.

(42.8 mm and 49.1 mm) over the p~riods of comparable record (1941-1984 for one-day precipitation and 1965-1983 for 24-hour precipitation). Gonzales Heights has more high and low valuC5, however (Tables 1 and 2).

Many moderate intensity precipitation events have higher

s.f". lUlIeT I Spatial DhJ'tribution of Heavy PrecipilOlion in Victoria II

Ti\, IIl£ I: Five highest ~nd fiv~ lowest o no-day p recipitation (ot1l15 ( min) Ut Victoria I nl~rnational Airpon and Victo ria G onzales Heighl¥, 1941.1984.

Five Highest (111m) f ive Lo west (mm) Gonzales Heights Airpon G on1.,les ileights Airport

U3 n,9 11.8 24.1 81.0 68.3 20.3 28.7 80.8 64.3 21.1 29.0 n, 62 7 24.5 29.2 68.8 59.0 24.9 31.2

Ti\, Hl£ 2: Four highest and four lowest 24 hour precipitation lo tals (Inm) at Victoria Internalional Ai rport and Victo ria Gunuties Heights , 1965· 1981.

Four Highest (mm) rour Lo west ( mOl)

Gonl.ah:s I kighL' AlrPQrl Go n1.aks Heights Airport

100.2 89.2 24.1 29.2 78.4 74.2 25.6 lSA 72.1 7).] 26.9 35.8 70. 1 69.5 29. 7 36.]

precipitation <It Victoria International Airport that at Gonzales Heights. The maxi mum one-day preci pitation values at the Airport ranged from 41.7 mm to 72.9 mm and had a median of 53.9 mm for the nine ~ torms examined here. The distribution of precipitation in this case (Figure 4) resembles that of the annu<ll precipitation (Figure 2). The intensity of precipitation was least in the southeast (Oak Bay) and increased both toward the west and north. Downtown Victoria received about IS percent more precipitation than Gonzales Heights; and the northern Saanich Peninsula and the southwest, 45 percent morc. The highest values were clustered in the central part of the region and particularly. at the higher elevations. The percentage deviations were fairly large, because the Gonzales Heighls precipitation was relatively low during most of these events, amplifying the percentage or ratio deviation. Still, the median difference in one-day precipitat ion IOtals between th e Airport and Gonzalc,~ Heights was 14 mm.

Although the regional pattern of precipitation resembl l..x1 that of annual total preci pitation, the magnitude ofthe deviations from Victoria Gonzales Heights was somewhat different. The deviations were greater than those for mean annual total precipitation in the northern and central parts of the Grealer Victoria region. They were lower in the west and similar through the metropolitan core. The relative regional variations were amplified in the storm preci pit ation distribution.

The composite map portrays the overall pattern of heavy precipitat ion ill the G reater ViclOria area. Six of the ten storms used for this

12 Climatological Bulletin / Bulletin climalOlogique 21 (1) 1987

~ D

N

I VICTORIA , S INTERNATIONAL AIRPORT

:b~ 8

Haro

1 1 Snail

• !€11 VICTORIA· HIGHLAND 1

1 Sa.nlch

I \1" ..... '"

([]) UlO-l10

0 111 ·1.20

8 VICTORIA· (I) 1.21-130 GONZALES

HEIGHTS () 1 31.1 ~o

8 ' . ' ·1,50 JV8n

€1 U.i H .60 de Fuca • > uso

Slra/l

FIG URE 4. Median .aho of .st.1lLon \0 Victoria GonzaJe~ lIeight~ precipilllllon for st(lrms when Victoria Inlernal;onal Airport recorded nlore pr(cipi lalion than Go"zaJ~s Heights.

map had il higher precipita tion total at Gonzak'S lleights than at the Airport. Th us, although the composite pattern (Figu re 5) is II combination of the two heavy precipitation patterns previously discussed, it is more rcminiscenl or tha! when Gonzales Heights has the heaviest precipitation (Figure 3).

S.£. 'Jlllle,. I ::'patial Distribution of Heavy Precipitation in Victorill 13

•

VICTORIA , o INTERNATIONAL AIRPORT

~~ Sl!Isnlch

Haro

S trait

• VICTORIA·

I I I

l01 HIGHLAND I

I I

JU8n

Saanich

de Fvea

Strall

VICTORIA· GORDON HEAD

0 <ID

VICTORIA·

° GONZALES HEIGHTS (J)

9 e1 •

~ N

I

~ a5

001 .05

1 ()6- ' , G

1 \6125

1261Y.i

I.l6-US

,. 1'5

FI G URE~. Compmile mlip of t lte median ratio of mil ion 10 Viccoriu GOll7.ales Heigh ts precipitation fo r Iht 10 h,gh <!lil precipi tation storms at tWO m[ermcdinlc stations,

Precipitation increased both nOrlh and west fro~ Gonzales Heights and reached a maximum of 50 percent more at the western stations (Figure 5). Another zone of low precipitation oc(.'urrcd in Ihe central and northern portions o rtlte Saanich Peninsula where "alues ranged from just sl ightly higher

14 Climatological Bulletin I Bulletin climatologique 21(1 ) 1987

than those at Gonzales Heigllls to about JO percent less. A preliminary assessment was made in order to identify possible

causes of Ihe .difference in the two distinct patterns of heavy precipitation in the Greater Victoria region. It must be cautioned that this is a preliminary discussion designed simply to indicate some plausibk controls on the basis of their association with one or the other of the dislinct patterns. It does provide a useful flfSI step, however. Further analysis based On more complete data and focussing on the actual mechanisms of effect is a project for fUlL!re research.

Hourly surface wind direction showed a great deal of variation but was primarily rrom the southeaSlern quadrant at the two major stations during most storms regardless of the pre(.ipitation distribution pattern. Thus, the differences in exposure to surface winds is not considered to be a major cause of the difference. The storms seemed to track from south west to northeast and the cent re of the low passed north of Victoria in most cases. Neither surface vapour pressure nor relati ve humidity, taken as measures of the relat ive available moisture and sat uration of the air mass. showed any consistent pattern. The front type and age of the storm did differ somewhat betwecn the two cascs. Storms that brought more precipitation to Gonzales Heights seemed to be somewhat younger wit h more distinct warm and cold fronls. Those that produced higher totals at the Airport were farther into the occluded stage. Eight of the ten fronts that passed over Victoria during the ., Airport-greater" storms were at least partially occl uded, whereas only three of the 10 "Gonzales -greater" fronts could defin itely be labelled as occluded. The front type did not produce a perfect differentiation of the storms into the two categories, however. Combinations of fro m type with ot her storm characteristics mentioned previously did not produce II perfect separation either. Given the difficulty of specifying front type from daily weather maps, however. some innucnce of front type cannot be ruled out.

The key facto r that did the best job of differentiating the storms when Gonzales Heights had a greater precipitation from those duri ng which the Airport had the greater tOlal was upper air wind direction, The 500 mb wind was from the southwest quadrant during all bUI one storm when Victoria International Airport had the greater precipitation. It was from the northwest quadra nt during all of the storms when Gonzales Heights had the higher total. The one storm that did not fit into the proper category on the basis of upper ai r wind direction was that of December 7 and S, 197 1. The Airport received the higher precipitation total despite the fact the upper air wind was from the w~t-noI1hwest. The difference in precipitation between the two stations was not great. The Airport received only 5 percen t (2.6 mm) more tOlal precipitat ion on the day of the maximum. The total precipitation in this storm was composed of both rain and SIlOW. Victoria International Airport reported 23.9 mm of rain and 24.4 em of snow. Gonzales Heights recorded more rain than the Airport (34.0 mm) but much Jess snow (9.4 em). The recording rain gauge data at the two stations showed high(.'1' intensity at Gom-..aJcs Heights fo r

S.£. 1hller / Spatial Distributioll of Heavy Precipit(ll ioll in Victoria IS

all periods fro m five minutes through 12 hours. Hou rly air temperatures on the day of maximum precipitation did noL show any important difference but t.he mean dai ly wind spt:ed was much higher at Gonzales Heights (35.4 km/hr compared with 21.7 km/hr). Thus, it is quite possible that the higher wind speed at Gonzales Heights reduced the catch of precipitation, especially the snow, and a greater underest imate of total one-day pr~cipi tation, occurred at this station.

The precise reasons for the different precipitalion patterns with nOflhwest and southwest upper air Ilow are not known for sure. A couple of possibilities might be dilTcrcnt patterns of orographic clrects or convergence in the region. The recording rain gaug'! data fro m Gonzales Heights and the Airport general ly reveals that the station wit h the highest one-<iay towl precipitation also lJad a higher intensity for shorter time pcriods as well. The except ion is the anomalous storm of December 7 and 8. 1971 discussed above. This would point to greater relative uplift or more humid air producing h'!avier precipitation in the locality of the stat ion with the highest total. These data plus summary comments on the day's weather pUblished in the Momh/y Meleorological Summary indicate intensity of prccipitation rather than duration had the dOlninanldfect on differe nces between thcsl.'. two stations. Victoria Gonzales Heights is located only 27 km fro m Victoria International Airport. DiOerences in atmospheric water vapour would not be enough to cause the observed variation in storm preci pitation. Thus, the factors that may innucnce the relative rates andlor levels of uplift would be the logical place at which to begin an analysis of reasons for the dilTerent distribution patterns.

Orographic elTects should be somewhat reversed between southwest and north west flow. The Gonzalei> Heights area is farther from the hills of Vancouver 1!>land than is the nort hern Saanich Peninsula wiul southweste rly winds but is closer wit h a northwesterly. The rain shadow of the Olympic Mountains does not protect any part uf the Greater Victoria region with a northwest wind and the southern part of the region is closer to the windward side of the rangc itnd beller posit ioned to receive any precipitation building back upstream. Stations located south and east of Victoria on the north coast of the Olympic Peninsula usually received less precipitation than did Victoria Gonzales Heights during storms wilh a northwest wind, whereas those farther west out of the lee of Vancouver Island, usually received more. Thus, any contribution of uplift over the Olympic Mountains is problematical.

Assuming that lower level 850 mb or 700 mb winds approximatc the 500 mb flow, the effects of convergence as these winds interact with the topography could potentially contribule tn different precipitation distribution patterns wit h differenl flow directions.

4. SUMMARY

The distribution of precipitation is a subject Ihal has long intrigued

16 Climatological Bnlletin / Bulletin climatologique 21(1) 1987

clim::tlologists both for its own sake and because of its important practical significance. '1l1\! distribution of heavy precipitation is an importtlilt subject in applied climatology. Most studi e.<; of heavy preci pitalion have looked at its tem poral pallcrn at a particu lar station rather than its spatial distribution on the m\!So- or microscale. Studies that have looked lit the distribution have mosl frequently addressed ooly one or two particularly severe storms rat her than the climatology of intensc precipitat ion.

Commcnts received from engineers during and after a seminar on sturrnwatcr management revealed that there is, indeed, a great deal of interest in the variation of heavy precipitation over small regions among those who have \0 design roads and structures to accommodate the precipitation. One rea.~OIl for the lack of c1imatologies of heavy precipitation is that over much of Canada, where convective summer storms are responsible for most of the heavy precipitation ewnts, the. dis tribution can vary markedly from storm to storm. Areas where the distribution of heavy prl.!cipitation r\!Su lt s from the interaction of large, mid-latitude cyclonic storms with orographic contro l,~

should show a more consistent pallcrn and lend themselves more readily 10 a cli matology of heavy precipitation.

T he raintall intensity-duration frequency tables produced by the Hydrometeorology Division of the Canadian Climate Centre confirm the finding of utis study that Gonzales Heights and the southeastern pa rt of the Grealer Victoria region can expect more intense storms than Victoria Intcrnational Airport and the north. The Airport has higher rainfall intensity over 5, 10, 15 and 30 minute duration fo r return periods fro m twO thro.ugh 100 yearS". Gonzales Heights has the higher val ues for durat ions between ooe and 24 hours for the 50 and 100 year return periods and between two and 24 hours for the 5, 10, and 25 year return periods. Caution must be used when evaluating these compa risons, however, because of the marked difference in record length between the two stations.

This study has shown that it would be a great mistake to assume the dist ribution of heavy precipitation is always the same as that of the mueh better known distribution of annual tOial precipitation. The two basic patterns fo und in the Greater Victoria region seem to be most closely related to upper ai r wind direction although fronta l type may also have some innuence. The distribution paHern with southwesterly winds, the common upper air now pattern during storms un the coast, resembled that of the an nual precipitation . The relative differences between stations were augmented during the heavy precipitation events, however. A somewhat different distribution pattern resulted with northwesterly upper air now.

The Variat ion in heavy precipitation, like that of total precipItation, wa~ great enough throughout the region that it would be imprudent to use the data from one SUit ion to represent the amount expected in another area. The present study has indicated the relative variation that might be expected across the region based on the available station network , but the precise microscale

S.l:: 1Jlller / Spatial Distribution of Heuvy Precipitation in Victo,.ia l7

pattern throughout this area of "aricd topography will probably ne"er be completcJy resolved. 11 i. .. hoped, however, that the preseot study has increased our understanding of the precipitation climatology of the Grealer Victoria region, highlighted some of tile variation in distribution patterns that cal) occur, and stimulated interl:st in some of the possible cont rols of the two different panerns.

ACK NOWLEDGEMENT

The usefu l advice of Mr. Norm Dressler, his staff at the Victoria Weather Office, and Mr. Terry Duffy of the Gonzales Heights weather stalion during all phllses of this study is greatly appreciated. The suggestions of Mr. Rodney Chilton hel ped improve an earlier version of Ihis paper. The contribut ion of one of the referees who supplied th e rainfall intensity - durat ion freque ncy data is also aCknowledged.

REFERENCES

Atmospheric Environme nt Service, 1982: CtII/aditln Cliln/J/e Normals, Voluml' J. !'rcciprlllliml. Environ ment Canllda, Otlawa.

Chilton. R.R.I-I " 197]: "Climatk_ Summary for Greater Vk'toria Region," pp. 5-2 1 in C.V. Slanley-Jones and W.A. Benson. eds. , An Im'clI lory o/l .alU/ RCSO llrccs alld Rl!source Polentitll.1" in the Capittll Regional Dis/ricl, B. C. Land Invtntory, Victo ria.

Cnligado. M., 1980: May-Sl'plell1ber frecipil/lliol/, Victoria , map produced by Air

Mllnagtment Branch, B.C. MinisirY ofEnvironm;.-n t, Victorla. Klein, W.H., 1957: Princi{lal Trllcks and Mt:an Prequl'IIcies 0/ Cyclones mId Anlicyclones

ill Ihe NOr/hem Hemisphere, U,S. Government Printing Office,

Washington, D.C. National Research Council of Canada. 1975: ClimfJlic In/ormation/or BUilt/illg Design in

CanadfJ. Naljonal R\;S!;arch Council, Ottawa, pp. 37-47.

Walker, E.R., 1961 : A Synoptic Clim%logy of Pam of /he Wes/em Cordiacra, McGill

University Arc tic Meteorology Research Group, PublicationS in Meteorology No. J.s, Montreal.

18 Climatological Bulletin / Bulletin climatologique 2 1( 1) 1987

Synoptic Weather Conditions During the Porter Lake Experimental Fire Project M.D. Hannigan and/.B. Hal'riflguJIl Pct;)wawa National Forestry Institute Canadia n Forestry Service L0riginal manuscript received 7 October 1985; in revised fo rm 20 August 1986)

ASS"! 1111(1

During II series of lin.' behaviour tests in black sprucc:.lirhen woodland near Porter Lake, Northwcst ']crrilories (101"8S"W, 61 <>7 9"N) the last fire or the series e~apeJ

confinement und burned over 1430 hectares. T his report investigates the. synoptic

weather conditions from June '17 to July 26, 1982, bracketing the Icst fire period. It was found that ~trong surface winds on July 7, 1982. ccmlriblllcd \0 the

escape of the fire. These unexpl:(;\cdly strong and persistent winds resulted fro m a deep cOllvective layer near the ground linking the surface wi nd 10 the lOwer extremity of an

uppcr level jet slrc:Jm. Such winds could nOI have been predicted without the hdp of an

e>:pcrienccd weal her forecaster,

Lors d'une sl:rie dc tests vlsam fro etudiel Ie comportement du fetl dllrlS tlnc forcl clai re

compoiiie d'eplnctles noires (;1 de lichens pm de Po rter La ke dans Jcs 'Jbrritolres-du­

Nord-Ouest ( 107"88"0. , 61"'79"N.), Ie derl1 ier feu de la s~rie 11'.1 pu c!tre tontel1u et S'CSI

propage sur [4}0 hectares. Dans cc rapport, sont ctudil:cs les condit ions synopliq ues du

temps du 21 juin au 26 juillct 1982, inlefvallc comprenanl la pl:riode des tests. On a decouvert que de forts venLS de surface Ie 8 juillet 1982 ont conlribuc

:\ la prop:Jgalion de feu hOTS des limites fiXl'cs. Ccs vents rom ct ~rsi~ tanl~ qui n'uvaient pus ete prevus san! dus a la fo rmat io n pres du sol d'une couche de convc:ction

profoode reliant Ie vent de surface a I'cxt remitl: lnfcriture d'un courant-jet oil haute

alti tude. De leis vcnlS n'auraient pu I!tre prcvus sans I'aidc d'un prcvisionnistc

eXpCrimente.

1. INTRODUC'rJON

On July 7. 1982 an cxperime nta l fi re ignited near P orter La ke, N. W .T . went

o ut of control, burning over 1430 hectares before being declared extinguish ed on July 26, 1982. T he behaviou r o f forest lires is dependent on the fire

environm ent w h ich includes the infl uen ces o f topogra p hy, fuel a n d weather.

M.D. FIQlllTigall and i.B. Harrillgton I Weather During POrler Lake Fire Project 19

/

>0 , I

I I

I , I ,

/ I / )

"' ... Whitehorse ",' . I ~, \

........... ';'i' '\t\ ~;';;'Porter Ed ' L k .... ~ ..to nnaoloe -r- _ Lake·

I F~t· -"-----'--

/ Smith ~ 'ChUfctllll

I , I I I I I I '\ Edmonton I rrhe~, I \. • I I I

\ 'SOSkotoon~ \ lJoncouve'\ I · \ \ (\

'I I • Thunder w ~~-'i""T"- L _ ~ Win'r ipeg· . _h._. !~!

0.. _4 90 km I '\ - - "j - ;6~'\

FIGURE I. Western Canada.

This report investigates the weather conditions on the days preceding and du ring the escaped li re. Emphasis is placed on the wind, which appears to be the principal meteorological factor.

The escaped fire was last in a series of tests conducted by the Canadian Forestry Service (CfS) and Indian and Northern Affairs Canada (INAC) to investigate fire behaviour ill Ihe upland black spruce (Piceo mariana) - open lichen (SlCreOl'rlu/on paschall') woodland fuel type in Ihe subarct ic region of the Northwest Territories (Alexander eJ uf. 1987). A suitable study area was fo und at Porter Lake in the Caribou Range (61 °43'N 108003'W), located 290 km nort heast of Fort Smith and 350 km cast-southeast o f Yellowknife (Figure I). This site lies within the Po n er-Wignes 6eodistrict (Bradley OJ ul. 1982) at an elevation o f 425 m above MSL. The primary object ive of the CFS/INAC experimental bu rning project was ID igni te a series of small-scale test fi res over a broad range of weat her conditions and mo nitor the re.'IuJling lire behaviour characteristiQ';. The resulting information was to be utilized in the develDpment of a quantitative scheme Df fire behaviour prediction for use by fi re managers (Lawson el al. 1985).

Nine experimental fires were successfully conducted and documented ovef a fa irly wide range of burning conditions as expressed by the Canadian Forest Fife Weather tnde" (FWI) System (Canadian Forestry Service 1984) during the aftcrnODns between June 27 and July 7. Data from

20 Climatological Bulletin / Bulletin c1imatologiq ue 21(1) 1987

I"r'l YLt l. SC'l u c nce("\r U~" 1 fires,.( fOu rI er Lake, Norc h weM Tcmlorio; ·

Rate of IgnitIon spn:nd

Date Test Fire Tlm~ MDT m mill I Comments

J Ufl~ 30 Ll "'0 6 No conlro) problems

J uly 1 L2 1519 26 Two spot nn.'lI' (65 mjump di~tancc) no cont rol problcm~

J uly 5 I.l "I" .. No cO'll ro l prob le ms

J uly 6 '-, 1510 , Nt) contro l problcms

J uly 7 '-S 1517 3J File escap~s plO I III IS24 reaches a bay o n Po ner La ke 8t 153 1 wi lh IIverage mtc of spn:nd 51 nl Inin"'

- Dala from i\1e~andel cl al. (1987),

five experimental fires is shown in lable I. It is clear that condit ions on two of the tcst days produced rapid rates of fire spread and spolti ng in advance of the fire frOIl t. The buming plots varied from 0.02 1.0 0.65 ha in size. The final experimental fire which was ignited at 1517 MDT on J uly 7 inalivenently escaped the l:onfincs of the plot area and spread downwind in a southerly dircr..1 ion ali a high-i ntensity, frce-burning crown fire (Alexander elul. 1987) for nearly 4 km by 1735 MDT. Fire CR-6 altainoo nearly 55% of its final size 0("= 143f) ha during the burning pt riod on July 7.

2. OATA AND OBSERVATIONS

Meteorological data acquired for the period June 27 to July 26, 1982 included hourly surface observations for Fort Smith, Ennadai Lake, Fort Reliance, and Fori Resolution. Also induded are two to three surface weather reports daily rrom forcstry stations at Tsu Lake and Snowdrift, Upper air observations for Fort Smith, The Pas, Churchill, and Baker Lake, as well as satellite imagery for the period July 6 and 8 arc also examined. In addition, selected surface and upper air analyses were obtained.

A weather station established June 26, 1982 at Porter Lake was equipped with a Forest Technology Systems Fire Weather Station 61OQ...24. The station included a Dowileasler model WV II Type 2 anemometer, a Downeaster model WV I Type I vane, a hygrothermograph, Goertz fan ventilated psychrometer, Taylor Clear-Vu plastic rain gauge, and a bi-metallic actinograph. A 10 minute average wind speed was measured at Porter Lake at 10 meters above the ground in a forest dearing whose diameter was five limes the tree height. This speed should equal 60% of that observed al an airport site (Oliver 1974, Silversides 1978, Simard 1969, Turner and Lawson 1978). During the test fires, additional observations of maximum gust speeds were taken every two minult!S.

MD. Flannigan and J.B. Harrington I Weather During Porter Lake Fire Projcc121

N T"'SLE 2. N Noon rnet~oro]ogicaJ ob5crValioo$ and components of lite Canadian For..sl Fire Weather I nd~x 11984 versioo) al Porter L:d:e,:-I. W.T" 1982,·

Staning Vatu .. : S5·FfMC 47-PMC 175-0C

D., Temp 'H W' RAINt

" 0 <c % KM/H "" WD FFMC DMC DC '" BU' 'W, OS> , " 17.8 " 10.0 0' NE " " '" ,., " " 3.43 , " ]].7 " '.1 0.0 , 8' " 'I' H " II 1.94

Q , " 22.2 " ,., 0.' " .,

" 'OS M .. " 4.7J , " 25.9 " 13.0 0.0 S " 62 ,.. 9.' ro " 7.M

3 , , 26.3 " 18.1 '0 S< " " '" 15.6 " " lUg

• , , 16.2 " 9. ' , .. E '" " '" " " , 0."

~ , ro., " ,., V NE " " 216 0.- "

, /),02 , • 19.(1 " 18.9 0.0 NE " .. ))) ,. " B LlO

". , , 15.9 ~ 18.1 0.0 HE " " 2<, ... " D W. n , , 19.4 " 0.0 0.0 HE " " '" , .. 10 " 5,34 "- , , 27.4 " J8.1 0.0 HW " " ~, ll.l " '" JI.~

'" , , 25. 1 " '0 0.0 ,W " 6J ". M " " '.n

=- 1 9 2l$ " 12,2 0.' N 90 " 272 '.0 " " 7.54

;r , " 19.5 ., 11.8 '.8 E " " '" <.l " • 0.39 , II JS.$ " , .• 0.' NE " " '" '-0 " • 0.99

3' 1 " ,.,

" ... 0.0 SW 81 " '" 1.1 " " 2.]1 , , " 20.1 " 12,3 0.0 'W " " m '-' " " 4.20 , I< m " ,u 0.0 H 9() " '" .. , " 2< 1.62

'" 1 " ,<1 " "J 00 NE .. " ro' '-' " " sro =- ,

" IS.S " '.0 0.0 'W 90 " ,I< " 81 IS '" n , " 21.7 " 1/).8 0.0 'W 9() 10 122 , .. 90 " 7.47

~. , " 17.1 " 17.4 0.0 'W .. " '" 1.> " " 8.01

0 , " '" " .. , 21.0 NW " " '"' 0. ' ., 0 0.00

0- , " 9.' " '.0 12.0 NW ,..

" ~41 0,' 2S 0 '''' 3 , " 10.1 " 10 0' NW " " '" ,., '" 0 0_1)1

• , " "' .• ~ !l.S 0.0 SW " " '" " " , 019

0; , U 19.5 " 13.1") 0.' NE .. " '" •• " • w 0-

, " 22.6 " IIJ 0.0 E " " 21' '-' 19 " 2.19

". , " 21 ,7 " 11.7 0,0 W .,

" m 5.4 " Ll 2.4]

" ,

" ,'-, .. ••• 0' 'W .. ,. '" " " L) 2.47 c • [)-,<l& from Aluander <I 3.1. (1987). t 24 hour ending 81 1300 MDT. 0

N 1"'0T£5

~ The FWI c; comprised of Ihree mo1Jilll~ (O<kJand I"''' Inl.rmcdiale codea . The Ibr"", mo;'lur. codes ,epr=nllhe mOl .. ",. ~onl.nl offine fU<I. (fine Fud Molllu.e Code FfMC), loosely ~ompa~lCd du{f(Du(fMoi'lu~ Code, OMC). and ~ompaci orpni<: <OIl (Drought C<><k, DC). Tht tWO Intermediale Indke'i. ",h,eh ar. cleri-·cd f,onllhe "';'istu~

~ cod .. and lhe luna"" wind. indica,. Ih. "". of inilial fire spread (Inil'al Sprnd Indu. lSI) and lotal avan~blc fuel (Build Up IndeX, BUI!. The: lwo ,nle.mediale illdo= are

~ combined 10 obl,llin Ihe FW l lI'hieh lepf$nlS Ihe ,nlcosily or Ihespl •• ding lir •. The Dail, s.:.-only Raullll (DSR) is an e' pon.n!ial fUJ>(:flon oflhe FWI cltsiaoed 10 .~plain Ihe 00 ",pi<! lOcreaS. of B.ea burned with fi ... i... WS'"' ,.ind speed. WD:. ",ood di . ection. ~

TA8lE 3. Summary of Wl:ath~r condition., fir~ danger ratings. and lirt behaviour characteristil:S during th~ tllpcrimental ftr<:s - Porter Lake project.'

Time of (ire (MDT) Dry-bulb Relallve Wind CFFWI components Rate of temperaturt' humidity 'P"" sprt'ad

Fire Date start " d (0G) (%) (km/h) FFMC DMe De SUI FWI lSI (m/min)

LINE SOURCE IGNITION F I RES LI June 30 1540 15" 26.3 30 20.4 92.] " "" 71 17 16.1 61

L' July I 1529 1m 24. ' " 24.0 92.8 " 112 74 " 21.3 26.3 Ll Jul~ 5 140; 1428 20.0 28 17.0 89.4 51 '" 67 " '.J J.5 1.4 July 6 1519 1542 2l.S J6 14.5 90.1 " '" 71 " '.1 37 L5 July 1 1517 J524 27.5 JI 28.0 92.0 " 25. " " 23.5 33.3

'-'At Jul~ 7 ]524 1531 Z7.5 II 34.6 91.9 " '56 " " 32,9 51.4

• Data from Alexander el al. (1987). t Between end of Plot 1.5 and bay or Porter Lake.

TAIILE 4 , PUrlcr La ke weather extremes June 21~J u l}' 17,'

Te lllj1<:rawre RI [ WInd Speed M", Min t.hx Mill M3~

Dale "C '" km/ b

Jllnt lJ " 3 . 1> " IJ

" 2J 7 " " 12 29 " 10 6J " " 30 " 12 50 29 21

July lJ IJ 71 " 2J 2 " 11 ,., 66 IS

J 2J 11 9<) 41 IJ , " • 80 " 21

S 21 , " " " 6 " 3 80 " " 7 28 • 7' 19 " , 26 IJ 78 32 t , 2J 11 90 4] t

10 20 t t " " 11 17 11 " '0 II 12 21 • " 20 9 IJ 23 10 " ]] " " 26 11 " 23 15 IS '" 6 7J " " 16 22 4 OJ " " " 24 10 66 28 15

• Data from Ah:'l(3niler tl al. ( 1987). t mi 3smg data Weather ob!'erv~tI tlnre a day at 1300 MDT after July 17. I'rel;ip ilal illll for Ju ly IS-July 26 3rC in Table 2,

While the study was in progress the FWI (sec footnote Table 2) (Van Wagner 1974) was calculated on a daily basis. All components of the FWI. along with Ihe Daily' SeverilY Raling (DSR) and meteorological observations from noon local standard time, are given in Table 2. A summary ofweathcr conditions, fire danger ratings, and lire behaviour characteristics fo r each experi mcntal fire was prcpared at the fire site by personnel of the Canadian Forestry Service. (CFS) (Table 3). Pertinent meteorological extremes during most of the study period arc given in Table 4.

The upper air flow During the laller part of June 1982 the upper level pressure pattefll over western Canada was dominated by a high-lutitude block (Figure 2). On June 27 a warm high over the southern Yukon was directly north of a cold low located off the coasl of southern British Columbia. This pressure pattern resulted in a northerly upper air fl ow over Porter Lake. By July I the high had moved eastward to the Mackenzie River valley and the cold low had moved southeastward into Nevada (Figure 3). During the next few days a series of

24 Climatological Bulletin / Bulletiu climatologique 21 (1 ) 1987

V~I7---' / , I

I~-I ' ''''';:'--;-' __

FIG U I~[c 2. 50 kPa a nalysis valid June 27, 1982, UiOO MDT. Uni rs are dccarnclers (heights, solid linc) and ·C (lcmpcralun,. dashed line).

\b \

,.,

'( \

I' H~\ 1\ \

..... I ~ «lS69 ~ Af"\ \'1._ "67 '-. I .,...- - . , ~-

I " I I

I " / \ / \

~. , - . \ I ~ 10 / '<0 I

Q'7 400 km I r~

fiGURE 3. 50 kPa analysis va li d July J, 1982,0600 MDT. Sec Fig.. 2.

M.D. Flannigan and 1.B. Harrington / Weather During Porter Lake Fire Project 25

lows moved into the Washington-Oregon coast, and thence northeastward into the central Alberta-Saskatchcwan border area. By July 5 the high was centered over Great Be-.l r Lake, with a low remaining quasi-stationary near the Alberta­Saskatchewan border. A cold pool of air and associated low moved to Wager Bay, located 300 km northeast of Baker La ke (Figu re 4). On July 6 the low in Saskatchewan drifted slowly eastward re-forming the familiar omega block shape. The Wager Bay cold low moved sou tb over Western Hudson Bay (Figure 5). Associated with this upper air pressure pattern was a north-soUlh jet stream extending from Victoria Island to eastern Great Slave Lake. The cold low over western Hudson Bay strengt hened and drifted southward to lie just east of Churchill, ManiWba by July 7 (Figure 6). During the same day the jet stream shifted eastward to lie in a north-south line just east of Porter Lake. On July 8 the cold low moved southeast along with the 'main pulse' of the jet stream (Figure 7). The blocking ridge remained as the dominant feature in the upper level prl!Ssure pattern until July 19 when a cold low from the Gul f of Alaska moved into the southern Mackenzie District .

The sUrf act' weather pattern At the surface:l nonh-soull l ridge of lligh plessure ovel the Porter Luke ale:! on June 27 (Figure 8) proceeded slowly eastward. The resulting moderate southerly flow of warm dry air persisted until July 1 (Figure 9). The warm dry weather came to an end as the easterly flow around a quasi+stationary low pressure area located near the central Alberta-Saskatchewan border hrought cooler and moister conditions to the southern Mackenzie District. Further north, Ii high pressure ridge extended sout hward to Great Slave Lake creating a moderate east to northeast now over the Porter Lake site (Figure 10). On J uly 5 and 6 this area of high pressure moved southward to the Great Slave La ke area, resulting in a decreasing pressure gradient over Porter Lake (Figu re I I). Ry .l illy 7 tjlC higll blld moved to sout hcrl1 Saskatchewan with a we<-lk ridge extending northward to G reat Slave Lake, allowi ng the surface pressure gradient to remain weak (Figure 12). During the sa me period the low moveo from central Saskatcbewan eastward to northwestern Ontario while another surface low over western Hudson Day was gradually deepen ing and moving southward. The Hudson Bay low continued to intensify as it moved to a position just northeast ofChurehilJ. The extreme cold of this low, in cont rast to the warm air associated with the ridge near Porter Lake created a strong temperature gradient aeross the intervening area. It was this extreme temperature conlrast, both at the eanh's surface and aloft, which led (0 the development of strong surface winds during the last experimental fire.

3. DISCUSSION

Strong surface winds were an important factor in spolling ahead of the Porter Lake fire and in its ultimate escape. On the basis of the tcst fire days at

26 Climatological Bulletin I Bulletin c1i matologique 21{l) 1987

,I I

Q ,~o

-- --~ 52

Q

FIGURE 4. 50 kPa a n aJy~is valid July 5, 1982,0600 MDT. See Fig. 2.

FIGURE 5. 50 kPa analysis valid J uly 6, 1982. 1800 MDT. Sec Fig. 2.

M. D. FlannigalllJlld 1. B, Harrington / Weather During Porter Lake Fire Project27

". o

) I I ) I

" \ 00.514 ~, \

"' ,'1 , '-, r- - - J, '"<.::1+1 h IT \ I ,"

I

I I I, I '( I

~I , • I I

I~ IT ~ _)' ,....,-.~ 400kml I,

FI GU RE 6. 50 kf'a analysis valid JlIl~ 7, 1982, 1800 MOT. The arrow indicatt'S the location of the Jd core, Sec Fig. 2.

==-.......,=--' - - --i-' 10

FIGU RE 7. 50 kPa analysIs valid J uly 8, 1982,0600 MDT. See Fig. 2.

28 Climatological Bul\elin I Bulletin climatologique 21 (1) 1987

-'-120 ii ' o 400km I, ~

FIGURE 8. Surrace ana ly~is v~lid June 27. 1982, 1200 MDT, Units 3r!' millibarl> (I kPa " to millibars) ,

F IGURE 9. Surface analY$is ~al id Jum, 30. 1982. 1800 MDT. See Fig. 8.

M.D. Flallnigan and J. B, Harring/oil / Weather During Poner Lake Fire Project 29

FIGURE 10, Surface aoal~sis valid July <t. 1982, 1200 MDT, See Fig. 8.

a

\ - , '_'1 ' - . 1'-- _ .

" ~ I I I I I I

" , \ \

•

\ , ~

PIGURI:: I I Surrace: analysis valid July 6, 1<Jlll, 1200 MDT. See Fig. 8.

30 Climatological Bulletin / Bulletin climalologique 21(1) 1987

FIGURE 12. Surface analysis v31,d July 7. 1982. t200 MDT. See Fig. 8.

Porter Lake it is evident that. for the fud type present, spotting ()ceul'I'ed when the Initial Spread Index (lSI) exceeded 20 (Table I and Table 3). Spotting occurred 100 m in advance of the escaped fire on July 7. These distances and the lack of Spot fires on other days were likely a consequence of variations in the fUt:1 moisture and the wind as renected in the lSI. Of these two variables, wind is by far the morc v~lalile and the more li kely cause of unexpectedly large fluctuations in fire spread rate.

Strong surface winds in the Canadian Northwest are usually caused by a strong pressure gradient associated with the passage of a shortwave trough or upper low. The relationship of shortwave troughs to major fire runs has been documented by Bmlak (1977).

AnOlIJcr cause of strong surface winds is the normal coupling of winds aloft with surface winds by the action of thermal convect ion. This effect may be particularly slrong in Ihe presence of a low level jct. The increased risk of extreme fire conditions when the wind proftle is characterized by a low level jet has been noted by Byram (1954). Brotak (1977) found a vertical wind profile c.\hibiti ng a vertical wind shear with strong surface winds (Figure 13) \0 be characterisl ic of most major fire situations in the t:aslern United Slates. Brolak also found thal one-third of major wildland fires had a low level wind maximum.

Before commencing to discuss the conditions leading to rapid fire

M.D. Flannigan and J.8. Harrington / Weather During Porter Lake Fire Project 31

'000

3500 / II

" 3000 • • • > 2500 0

/ • d

• 2000 • • " • • 1500 / " r 0

• 1000 r

/ /

500

o / o 20 40 60 '0

WIND SPEED (km/M

FI GU RE 13. Vertical Wind protile found by flrolak 10 be characlcri$tic of most m3jol fire silU8lions In the Easler" IIniled Slal~S.

spread on Ju ly I and July 7, 1982. it is important to notc that d ry fu el and strong winds were not the only factors involved. Differences in thc plot size, configuration and location along with differences in thc ignition pattern cou ld have played a role in the escape or lhe test fire ignited on July 7.

A low level jet a ppe;lrs In have heen the major factor in the rapid fire spread and spo t ling on July L On the previous day, June 30, the wind was light during the early mo rning hours despite a moderate surface pn:ssurc gradient (Figure 9). Nocturnal cooling had stabilized the surface layer of air and uncoupled it from the geostrophic wind aloft. By early afternoon the air near the ground had been heated suffici ently to cause active convection. As the afternoon progressed thermal convection extended through the nocturna l inversion linking the surface wind to the geostrophic wind alo ft . The maximum wind speed at the ground reached 2\ km h -I at 1700 MDT. By 2100 the reduction in incoming solar .radiation had reduced the level of convective activity and the wind had dropped to 4 km h-l .

On July [ the pre.~sure gradient was similar to that of June 30 but a low-level southeasterly jet centered at 1.5 km with a maximum speed of 50 km h- I was present, as shown by Ihe0600 MDT Fort Smith wind profile (Figure (4). Decreasing winds above the jet were caused by an opposing thermal wind above the jet core. In this case the opposing thermal wind was

32 Climatological Blllietin I Bulletin c1imatologique 21(1) 1987

·000

3~OO

" 3000 ~

> w > 2500 0 m • ~

2000 w "" "-i", " " w >

1500 ')

" " 0 1000 w

I

'00

V V

,/

/' -o

o 20 .0 60

WIND SPEED (~m/hl

FIGURE 14. V~rlical wind profile ~ I r Or! Smith . . July ), J982, 0600 MDT.

EFFECT OF SURFACE FR IC TION

EFFE CT OF OPPOS ING THERMAL WIND

150-1:500m \

\ \

WIND SPEED ---+ FIGURE 15. Vc rl ical profile of the wind velocity r~sulli og from lilt Interaction of surface friction and an opposing thermal wind (from Dickison and Neuman" 1982).

80

brought about by significantly colder air to thl! nort heast of G reat Slave Lake. The result ing wind profIle. similar to Byra m's type la (alt hough located higher abov!! the ground), is one or the most dangerous from a fi rt! control standpoint. Its struclUre has bet:.n illus\r8led by Dickison and Neumann (1982) (Figure 15),

The development of the surface wind on July I was similar to that on June 30, except that the presence of the low level jet caused surface winds to reach 2] km h- I

. T ht$e winds in combination with an additional day of

M.D. Hannigan and l .B. Harringtoll / Weather During POrter Lake Fire Project 33

drying were sufficient to cause the fire rale of spread to rC(ll;:h 26 m min+! and spott ing 10 jump 65 m ahead of the fire front.

Experimental fires were ignited on July 5 and 6 respectively, during a pcriod of weak pressure gradient (rigure II). Despite considerable instability during the afternoon hours, the absence of strong winds aloft led to light to moderate su rface winds, These winds combined wit h higher fuel moistu re brought about by the lingering effects of precipitation on July 2 and 3 (Table 2) resulted in there bei ng no lire control problems.

July 7 appeared to be an eq ually fi ne day for the final experimental firc. The day was clear and hot wit h low relative humiditil"S. The high temperatures were accompanied by a nOllhwest now as ai r moved in a clockwise motion around the warm ridge west of Porter L!lke (Figure 12). The low relativc humidities were a result of a balance between moisture added by evapotran~pira lion and subtracted by condensation on the still cold lakes. (The Lakes had been il;:c covercd only two 10 three weeks earlier), During the afternoon the winds increased to 35 km h- I and spott ing occurred 100 III ahcad or Inc fi re front. Finally the fire escaped control, jumped across a small bay on Porter Lake and eventually burned an area of ovcr 1430 ha.

To belp visualize the vertical wind st ructure over Porter Lake on July 7 a vcrtical cross+sectioll oflhe atmosphere between Fort Smith, N.W.T.

" " '0

9

, ,

CJ , ,

- .

FORT PORTER Tt1E CHURCHILL SMITH LAKE PAS

FIG URE 16. Vert ical C(()i i\--5I:CI' OIl ron Smith·Churchill, Jllly 1, 1982, lSOO MDT.

, 2

34 Climatological Bulletin / Bulletin climatologique 21(1) 1987

FIGURE 17. Infrared satellite imagery taken by NOAA-7 at 0700 MDT, July 6,1982.

and Churchill, Manitoba has been constru '""ted (Figure 16). Because of the paucity of upper air stations in the area, observat ions from The Pas, Manitoba have been displaced northward along the 50 kPa contour line through The Pas to a posit ion where the same contour line intersects the cross-section. Using the thermal wind relation, a cross-section was drawn in which the increase of wind with height and the slope of the isotherms form a consistent picture. According to this cross-sect ion a basically northerly jet core centered ncar 8 km lies juSt to the cast of Porter Lake (Figure 16). Strong winds associated with this jet extend down to within a short distance of the earth's surface.

Corroboration of the jet location can be found in satellite imagery. Figure 17 is an infrared satellite picture from NOAA-7 taken at 0700 MDT, July 6. The cirrus cloud streak extendi ng south-southwestward from

M.D. Flannigan and 1.E. Harrington I Weather Dr/ring Porter Lake Fire Project 35

FIGURE 18. Enhanced infrared satellite. imagery lake" by NOAA-7 at 1500 MDT, J uly 7,1982.

southeastern Victuria Island corresponds 10 tile position of the jet stream. AnalYSIS have shown that the jet core lies just to the cold side (east in this case) of the cirrus (Weldon 1979). A second NOAA-7 infrared picture taken at J500 MDT, July 7, shows a band of somewhat diffused cirrus extending in a nOflh­south line through Porter Lake (Figure 18). A dearing zone in northern Saskalchewan and Manitoba represents the most advanced downstream posit ion of the jet core (Weldon 1979). The July 7 satellite infrared picture also shows thunderstorm development south of Porter Lake, indicating extreme atmospheric instability at that time.

Using all available information, including upper air charls, tephigrams, and satell ite imagery the most probable location of the jet core at 1800 MDT on July 7 is shown in Figure 6. A vertical wind profile over Porter

36 Climatological Bulletin I Bulletin c1imatologique 21(1 ) 1987

" ~ • w > 0 • • ~ • • " • • " • ~ • •

' 000

" 00

'000

2500

2000

1500

'000

'00

° °

r7 /

II /

1/ 20 40 60 80 WIND SPEED (km! hl

FIGURE 19. PoslUlaled "enicaJ wmd profile al Punel Lake, JlIly 7, 1982, 1800 MDT.

6000

~~oo '\ ~

5000

J 4~OO 0 • \ "

4000 > 0

3~00 • ':\ • 0

" 3000 • " " 2500 >

" 2000

\}.,

\\ • ~ 0 1500 \ x

1000

500

.. \. \

~ - " ° -' 0 ·30 -20 -10 o '0 20

TE MPERATURE: I"CI FIGU RE 20. Venital ternperal llie profiles al Fon Sm;lh JIl]y 7, 1982, (1600 and ]800 MDT. The dMhed hne repl~nts the 0600 MDT plofile and the solid Jill(: leplesenl$ the 1800 MDT profile:..

' 0

N

60 0 0

5500

, 50 0 0

~ 4500

~ \~

" > w 4 0 0 0 > 0 )500 •

\ ~:-,

• " w )000

\ • " w 2 500 >

" 2000 , 0

w 1500 I \~ ,

1000

500

\ ,\ r

0 -40 -30 -20 -10 o '0

TE MPERATURE ('C)

FIGURE 21. Vertical temperature profiles al The Pas J uty 7, 1982. 0600 and 1800 MDT, The dashed line represents the 0600 MDT profile and Ih~ solid line represents Ihe ISOO MDT profile,

~

" > w > 0 • • " w • " w >

" , 0

w ,

6000

5500

5000

4500

4000

3500

3000

2500

2000

1500

1000

'00

o -'0

\ \ 1\

\ ,

1\ \

\ \ , ,

-)0 -20 - 10 o TEMPERATURE (OCI

FIGURE 22. Postulated wf\icallemprature profile at Poner Lake. July 7, 1982, 1800 MDT.

'0

Lake for 1800 MDT J uly 7, deduced frum the same information is shown in Figure 19, This profile bears a remarka ble resemblance to the situation in Figu re 13 which Srotak fo und prtsent in most major fire situatio ns over the easte rn United Statl:5. Om: feature of Figures 13 and 19 is the strong vertical she.1r of the wind in the lower atmosphere.

It has been mentioned earl ier that vertical mixi ng is required to bring strong upper winds to the ground. Evidence for strong thermal instabili ty was provided by the appearance of thunderstorms in the NOAA-7 imagery. Further evidence is provided by the radiosonde ascents from Fort Smith and The Pas (Figure.<; 20 and 21). The 1800 MDT temperature profil es from both stations sho w a superadiabatic lapse rate from the ground to 1.7 km and strong insiability extending to 3 km. A vertical temperature profile fo r Porter Lake at 1800 MDT (Figure 22) constructed from thc cross-section (Figure 16) also depicts atmospheric instability close to the ground.

The tcst fire was ignited at 1517 MDT on July 7, 1982. A combination of factors, including rclatively dry fuel and strong surface wi nds, caused the fire to spread rapidly (33 m min-I ). The fire jumped a sprinkler line at the end of the test plot at 1524 MDT. It advanced toward a 100 m wide bay on POrter Lake at an increased speed of 51 m min- I, jumped the bay and becam~ Caribou Range fire 6 (CR6). Tree-crown streets were obs~rved in the immediate area o f fire eseape which suggests the p resence of horizontal ro ll vortices as discussed by Haines (1982). Wildfire C R6 pushed rapidly southward o n July 7, slowed dramatically on July 8 and 9, and continued wit h flare-ups on J uly 12 and 17 until fina lly declared out on Ju ly 26. The tOlal area bumed was 1430 ha.

4. CONCI.USIONS

Strong surface wind$ were a major factor in the escape of the Porter Lake, N. w:r. experimental fire ignited on 7 July, \982. The purpose oCthe experiment was to test fire behaviour in this type of forest under the widest possible range of conditions, and from this po int of view the experiment was a success. The unusual winds were caused by the coupling o f the surface wind with a jet strea m alan through the action of strong thermal conveclion. These winds were a result o f synoptic scale processes and eQuId have been predicted through carefu l exami nation o f the data by an experienced weather forecaster.

ACKNOW LF.DGEMENTS

The authors wish to acknowledge with thanks the help of personnel from the western region o f the Atmospheric Enviro nment Service who supplied surface and upper air analyses, tephigrams. hourly surface observatio ns. and satellite imagery. Thanks are also due to the Fort Smit h Regional Fire Centre o f Indian and Northero Affairs Ca nada for the provision of surface observations from

M.D. Flannigan and J.B. Harrillgton I Weather During Porter Lake Fire Project 39

nearby forest ry towers. Mr. M. Alexander of the Northern Forest Research Centre. Canadian Forestry Service. p rovided meteorological a nd Dth!!r pertinent data from Porter Lake, and valuabk insight.

REFERENCES

Alexander, M.E., Stocks Ill., Lawson, B.D., and Van Wagner, C.E. 19117. Fire behavior in black spruce - licheo woodland: the Poncr Lake Project.

Canadian I'orestry Sen'ice, Northern Fore~ try Centre, Ed monton, Alta.

illformll tion Repo rt NOR-X-(in press). Br~~dley. S.W., Rowe, 1.S. , Tarnoeai, C., and Ironside, G.R. 1982. An ecologic3t land

survey of the Lockhart River map area. Northwest Territories.

Environment Canada, Lands Directorate, Ottawa, Onl. Ecological Land

Cla~itlca tion Series No. 16. 152 p.

Uyram, a.M. 1954. Atmo~phcric conditions related to blow-up tires. Station Paper No.

35, USDA Forest Service, Southeastern rorest expo SIn., Asheville, N.C.

34 p.

Brolak. 13.A. 1977. A synoptic slIIdy of the meteorological condit io ns associated with majo r wi ltJlamJ fires. Ph.D. ui~st:r tatiul1. Yah: Ul1iv .. New Haven, CU/III.

163 p.

Canadian Fort$try Service. 1984. Tables for the Canadian Forest Fire Weather Index

Systeru. Environmcnt Canada, Ottawa, Onl. Forestry Technical Report 25.

48 p. Dickison, R.B.B. ll nd Neumann, H. [-I. 19112. The occurrence of nocturnal [ow-lcV1:1 jets

in New England lind the Canadia n Maritimes. A/mos.-Ocean. 20:287-300. Haines. D.A. 1982. Horizontal roll vortices :lnd crown rrrc~ . J. Appl, Me/ I!Qral. 21:751-

763. Lawson, 13.0., Stocks, IU. , A1c:Kunder, M.E. aod Van Wagner, C.E. 19R5. A system for

]1~erli r:l i ne firc t:..' hav;or in (;Iln:uiilln forf.~ t~. tn: Prnr."I'I1in&~ nfthe Eichth

Conference on Fire and Forest Meteorology, cd. by L.R. Donoghue lind

R.E. Manin. Society of American Foresters. Bethesda, Maryland. pr. 6- 16. Oliver, H.R. 1974. Wind-speed modification by a very rough surface. Meteorol. Mag.

103; 141-145.

Silversides, R.H. 1978. Forest and airport wind specds. AIIIWS. -Ocililn. 16: 293-299. Simard, A.l. 1969. Variability in wind speed measurement and its ctTeet on fire dangtr

raling. Info, Rep. FF-X- 19, Can. For. Fire Res. Ins!., Ottawa, 39 pp.

Turner, J .A. and Lawson, B.D. 1978. Weather in the Canadian forcst fire danger rating

system. Environ. Can., Can, For. Serv., Pacitie Forest RI:-s. Cell., Victoria,

H.C., tllf., Rep. BC-X-I77, 40 pp.

Van Wagner, C. E. 1974. Structure of the Canadian Fores1 Fire Weather Index. Environ. Can .. Can. For. Serv., PubJ. No. 1333, Ottawa. 44 pp.

Weldon, R. 1979. Satellite training course note.~. Part IV: Cloud patttrns a l\d the upper

air wind field. U.S. Dcp. Comm., Nat. Environmental Satellite Service,

Applications Div. 80 p.

40 Climatological Bulletin ! Bullt:tin clirnatologiquc 2 1(1) 1987

Summary and Highlights of the 1984 Severe Local Storm Season by M.J. Newark l , M. Lcducl, L. LegalJ, F. Letch ford', S. Sioks, A, Wallace., and O. Waugh' Atmospheric Environment Service [Origin;] 1 mfl rlll ~cripl re.ceived 2 M:ly 19H6: in revised for m 6

October 1986)

AHSTRACl

Thi~ report provides un overview and summary of Ihe 19&4 severe Joc:Li storm season in

the broad region from the Rocky Mounta.ins to Quebec. Storm sla ti ~lics W{'rc compiled from the seasonal report prepared by each of four Atmospheric Environment Service regions, and arc summarized in lubul<lr form. Highlights of Ihe sell50n UTt' presented

fronl an ovcnlll point of view aud also by region.

Ce rapport donne un perspectiw. global el un sommairc du temps violent est ival de 1984 dans ];[ VlISle region du Canada des montaguL"S rocheusc:s jusqu'a Quebec. On a

compile les stat i$lique$ des orages du r:l.pporl saisonal qu'on prcparail :1 chaqu'un de;o; qualre regions de la service d'environncmcnt atmosphhlque(SEA), cIon les disposal!

ell tublcauJ!. On pres.:nlc geuer:tlcmcl1l les dOllS de lu SUlson et 011 les presente aussi par

region de ta SEA.

I. INTRODUCTION

This report has been compiled mainly rram lnrormation contained in the annual reports o r the 1984 severe local storm season prepared by the Atmospheric Environment Service weather centres in 4 regions (Western , Central, Ontario, a nd Quebec). The purpose is to summarize the statistics or the season and p lace them in an overall perspect ive, and to pr~ent seasonal highlights in narrative rorlll.

The stat istics should be interpreted with care because the definition (Table 1) or what constit utes a convective severe local storm varies rrom region

I CanadillU Climat~ Cenl/c. Downsvicw , Ootati!) Weather Ccnh'c, toronlO I PraIrie Weall1u Centre, WinnIpeg

Albnla W~athcr Centre. !:dmlliltOn , CCJllfC m~u~orologique c.lu Quebec, Ml>nlrcat

M.J. Newark er (II. I /984 Severe Local Srorm Seasun 41

TAIIU: I. Rc giOll81 Delioitioo~ of II ~cvcTe ConVl:etive Weather Event

WEST"~" REG tON I ) tornauo, w3ttrsPQul, or IlIonel ell/uu; 2) hail ~ grape-size (12 mm); 3) wind I!USt.~ 2: 100 kmlh; 4) T',liofall amOUIlt5 ~ 2.') mm io oo<! honr.

The orn;trvalion of any of lhe above condi tions, singly or together is ntcl:ssary for an ~ven! to be

labelled ~t~re. Some subjective ~cTcening is rcqoired to ciimlnate synoptic ~calc wtnd events.

(:[(\oTRAL HCJlON

I) tornadoes or wal~l"SpouIS; 1) hail ?:- 20 111111;

J) wrnd ~~~s or gnsl5 2: 100 kmlh: 4) rain amounts =:: 50 Olill within om: hour,

ONTA I(IO ~~GlOI'oi

1) torltJdo;

2) hail > 10 mm diall1eler: J) dDmag1n~ lhundcr~torm wind gusts or, if wimJs mCCIsurcd, I!US1 ~ > 80 ~m/h (44 kts); 4) nuodinV downpours.

OU (; UIlC ~1i{]JON

ObjecliVl: criteria: II tornado; 2 ) hail 2:: I.') nll" diamete r; 3) mong gu;tS ~S) km/h (45 kt~): 4) heavy downpour 2: 25 mmlh or, 2: 50 mm/24h. Subject ive crileria:

repOrt of maleriat damageor lossOI hli: tIf Injury caLl~ed by~ t rong wind!; or h~.J.vy down­pours.

10 rt:gion a nd Therefore. sirictly speaking, the statistics are not comparable from one region \0 anOther. However, because the defini tions arc SomewhaT similar, the numbers do approximate the picture <lcross part of the country. Counting the number of events is also a problem which is approached diflerently from region to region (see Seaion 2). Although a " nationa l" summary is provided (Table 2). it does not indude information front Canada's no rth. much of British Columbia, or from the Atlantic Provinces. Some severe local storms a re known to occu r each ye<lr in these regions, but a systematic record of them is not maintaint'd, and indeed, in some areas is im possible to compile due to lack of information. A map of the four regions is given tn Figure I , and il can be seen that they cover the part of Canada most susceptible to such storms.

2. RECORDTNG AND COUNTING EVENTS

From a climatological point o f view one would like to know the number of severc local storms obtained by treating cach obscrvation of a phenomenon a.~

42 Climatological Bulletin / Bullttin climatologiquc 21(1) J987

FIGURE 1

I~ IGURE J. RCI!:'ons muking a seasollal S~Vef<: local :slorlT' ~porl. Areas of populalion densiLy > I per klUl ar~ shown appwxima(~Jy by shading.

a d islinct event. These have been referred to as "proper-events" (Legal, 1984). In prm':licc, difficulties a rise when this is attempted because often there i ,~ nOI enough information available to distinguish each unique even!. Even when there is sufficient information, il is oat always possible 10 determine whethcr a series of da mage incidents very closely related in lime and space was the resul t of one intermittent storm , or a succession of independent ~ torms .

The Q uebec region circunlVenlS this problem by recordi ng sever~ local storms in terms of " region-events" (Siok, 1984). According to this scheme, weather occurrences which take place wilhin a given forecast region a re counl ed as a ile region-event provided they occur within an hour or so of each other. The remaining regions attempt to record proper-events. With re->ources that vury fro m year to year, and from region 10 region, and without a clear defini tion of what constitutes !J. proper-event, the num bers of events shown in lable 2 shou ld be trealed with great caution because it is not known how wen they represent the true numbers. The number of tornadoes is perha ps un exception because a greater cffon is expended on collecting information ubout them and idenlifying each one.

M.1. Nell/ark el al. / 1984 Severe Local S{orm Seasol/ 43

l'A8Le 2, Severe Local Slorm Summa,ry for 19&4

...

• "

" " • .. " "

" • " M = NQI known SOme stat,st ,cs In the "Nallonal" column ~ re notlruly represeotallve due to regIonal ,hffcrcncc5 in defimtion (see Tabk I). l! = Not indudiog waterspouts or funl\el doulls.

3. DATA SOU RCES

Rcport~ of severe local storms in 1984 were gathered as follows: (a) from the primary observing network of AES; (b) from volunteer weather watchcrs in each region; (c) from ncwspaper clippings; (d) from field surveys of storm damage (for example, Voak et. aL, 1984; Bcrtolone, 1985); (e) from contacts with tile m~dia, private individuals, provincial !"Igcnr;i!$, in~tLraDce companic~ etc.; (I) from the Environment 2000 mesoscale project in Manitoba (Legal, 1984). More detailed information concerning sources can be found in the individual regional reporls (Letchford et aI., 1984; Legal, 1984; Leduc, 1984; and Siok, 1984). h should be noted that the information is gathered primarily from populated a reas (approximately shown by the shaded areas in Figure I).

44 C limatological Bulletin I Bulletin c1imatologiquc 2 1(1 ) 1987

4. SI!ASONAL HI G HLIGHTS

4. 1 "National" Severe local storms (as defined inlable I) occurred on 81 days during a season which began on April 27th, ended on October Jrd, and lasted 160 days. The storms were: responsible for at least 4 deaihs and 45 injuries. In addition, at least another 5 people were killed by lightning. Perhaps the most notable outbreak of severe local storms occurred on J une 29th, when a number of tornadoes, hailstorms and thunderstorms producing damaging winds crossed northern Alberta while others lashed southwestern Saskatchewan. During this season there were 48 days with severe wind storms and 37 days with severe rain storms.

The tornado season was coincident with the severe local storm season and produced a minim um of77 tornadoes on 31 days. They were responsible for 2 of the deaths and 44 of the injuri~.

Severe hail occurred on 50 days during a season which began on May 12th, ended on September 2nd , and lasted 114 days.

Waterspouts and funnel clouds were considered to be severe local storms in some regions in 1984. There was a total of at least 9 waterspouts reported aod at [east 67 funnel clouds.

A summary of these statistics is provided in Table 2. Tablcs 3 to 7 show the days when the various types of storms occurred in the fou r regions.

4.2 The Western Region (northeastern 8.(:. ({lid Alberta) A comparison of the last three convective seasons from 191\2 to 1984 would. at first glance, imply a trend toward mon: severe weather days. with the increase not attributable to any particular type ofevem. Consider however, that the weather watcher network was operative during the 1984 season and responded with many reports of severe weather that otherwise wou ld not have been detected. It may then be stated that, absolute numbers aside, the 1984 severe weather season li kely had fewer events than 1983.

Reported tornadic activity has decreased the past two seasons when compared to the very active season of [982. Nonetheless the 15 tornadoes of 1984 were. nearly triple the long term average of 5.5 (Newark , (983). Of Ihc IS tornadoes, 7 occurred during thc outbreak of June 29th north of Athabasc3. Hence, When the number of tornado days is examined, the 6 tornado days in 1984 are only slightly more than the average of 3.9. It is certain thai some tornadoes go undetected or unreported due to the low population density. It is our hope that continued media exposure of severe weather, togcther with the weather watch network, will improve the detection of severe events.

An interesting stat istic shows that severe weather has been reported on one day in three for the [3l)ltwo summers. It is suspected that a better

!If.J. Ntwork el (Ji. / 1984 Severe Local Siorm Seasol/ 45

TANI f 3. Seven: l.OCllJ Stunn DIlY5. 1984

I - "UN lie: 1 • ALtA; J - SASK: " - MAN;.5 - NWM.'1 ON!'; 6 _ ON"; 7 _ $EMN UN I: g _ Qur: 9 - NAll0"~"L

, , 3 " 5 (, 1 8 , " . , • , . " 3 • , · " "" " • '" • • • • '" " • " • , • • " · "'Y " • • " • " • " • " • • • " • • • " • " · • • " • • •

" • \3 • • " • •

" • " • · " • • " • • • " • • ,. • " • " • • • " •

" • " · • " • 30 • " • " • • • ", • • • • " • 30 • • , • • " • • • • '"

, • • , • " • • • • , • " • • " • " • \3 • • " • " • " • • • " • " • " • • " • " • " • • " • '" 3 •

" • • " • • " • '"

, • • •

,

" • 3 • • 10"'- III 21 11 ", n 81

" • • , • " • , • • • • " • • • • •

" • • • • • " • , •

" • • " • • '"

, • " • • , • " • • • · • • \3 •

information gathering system is responsible for the higher number reported during the past two years. rather than an increase in severe thunderstorm activity. There were more severe events in August 1984 than in July, a month that is usually more climatologically favoured. This may be attributed to the lack of thunderstorm activit)' in southern Alberta due to drought during July of 1984.

An historic severe weather day for Alberta occurred June 29th when a complex or severe storms originated south of Drayton Vatley and tracked northeastward to Fort McMurray, a distance of nearly 500 kilometres. Along the path of the storms at lea.~t five tOrnadoes were spawned, hail larger than golfballs was reported. and wind gusts were measured al 100 kilomet res per hour. Two fatalities lmd several injuries were caused by the storm. Property damage alone ~xcceded one million dollars. On the same day a second line or severe thunderstorms developed in eastern Alberta. Two tornadoes and wind

46 Climatological Bulletin I Bulletin climatologique 21 ( 1) 1987

TAULE 4 . 'nlrn;,do Days, 19~4

I-NI'RNIIC:2_AI.TA; J_lIASK:

4 - MAN; 5 - JIIWkNOfolT; 6 -ONT;

7 - S~I(N ONT: 8 - QUE;

9 - NAfJON,o,L

, , " 5 " . ,

Ilpr " •

" • H', " •

" • " • 20 •

" • J" 1 • •

" • " • • " • • " •

" • " • " • •

'" , • • • • " • " • ,. • " • " • ,,' , • • • • • , •

" • ,. • " •

'"' , • " •

'" , •

roUL • " · " , "

lA!lU:' 5. Sc~erc Hail Days, 1984 J -I'I F.I{ N BC; 2 -AUA; J -SAS":; 4 _ MI\N; 5 _I'IWRN 01"'1': 6 _ mn;

7 - SERN ONT; 8 _ Que; 9 - NA110NAL

, , , " " , . , , , " 61 • ,

M" " • • '"' " • " • " • • " • '"

, • " • , • •

'"" • • " •

" • , • • • • " • • • " • " •

" • " •

" • '" • " • " •

" • • " •

" • • " • • " • " • • •

'"' • • " • 5 • " • • • • " • • • ,"p , • • " • , • " • •

" • • • TOTAL " , 13 2 " " " " .. " • " • " • • •

" • • " •

" • •

" • • • • " •

" •

1980, there were only 34 severe weat her days in 1984. Note that this number does not agree with the total obtained from Table 2 due to the overlap of some days from one province to another within the Region.

The season started with the Whitewood, Saskatchewan tornado on May 12th. Other dramalic severe weather events include the flooding in Ihe Winnipeg area in mid-J unc, the July 8th SI. Claude-Rosenort tornado, the family of waterspouts over Lake Winnipeg on August 8th and the Prince Albert wind storm of August 19th.

Two men were killed by light ning, one in Winnipeg on June 21st and another near Roland, Manitoba on July 12th. A third death was caused indirect ly by lightning ncar lockport, Manitoba on October 11th. The only fa tal ity due to severe storms was a passenger in a car which was blown off the road north of Thunder Bay on August 8th.

48 Climatological Bulletin / Bulletin cJimalologiquc 21(1) 1987

TABLE 6. Days with &:v~re t.oc~1 Wind, J9~" I _ J'lEilN IIC.; 2 - AL'A; 3 _ SASk; 4 - MAN; 5 - NWIIN OtIT; 6 _ ONT;

7 -SI:MN ONT~ 11- QUE, 9 - NA110NAt.

, , , II ~ 6 1 a , , , " · " ,

'" " • ... , • •

" • .. •

" • " •

" • " • '"" • • .. • • , • " • • •

" • " • " • " •

" • • ,. •

" • " • ,. • 29 • •

" • " • •

" • so, , • 29 • • .. •

'" • • • • " • • • • " • , • • " •

" • " • T01Al " ,OJ '" '''' " • " • " • • " • " • " • • " • •

" •

" •

" • ""

, • , • •

4.4 The Ontario Region (excluding lIorthwestern and extreme .foll/llea.ftcrn section o/Ontario)

Alt hough reports of severe weathl!f' were down noticeably from 1983. the summer of 1984 wa~ still above normal and will be particularly memorable in certain portions of the province. The first severe weather of note was all May 22nd when two tornadoes were reported in central Ontario. The last significant storm day was September 10th when three tornadoes occurred just south and southeast of Lake Si mcoe. August and early September was the most active period when severe weather was rep0l1ed on 10 days between Augusl 8th and Septembt:r 2nd.

The area around London was particularly hard hit in 19&4 with severe weather being reported on no less than ten days. The most notable event occurred on September 2nd when a major tornado did in excess of live mill ion

M.1. Newark et ul. I 1984 Severe Local S torm Season 49

-IA Hl E 7. DllYS willi B~vy Local R~IIl , 1984 1 - NI,~N ~c; 2 - AIT;',; J - S~K; 4 _ MAN; 5 _ NWRN ONT;

6 - o,-n: 7 - SI.'II.N ONT'. 8 -QUE; 9 - NAllONAL

, 2 1 , 5 (; 7 8 1 2 " 5 (, , 8 , lo4 ay 12- • Aug 18 •

" • " • 25 • " • 29 • " •

J", , • • • 29 • • 13 • 10 • " • • • " • TOTAl. • 1 '" 1831 ,. • • " • 20 • 21 • " • • " • '", , • , • 11 • 12 • • 13 • ,. • " •

" • 20 • •

" • 29 • " • ,,' 2 • , , • , • • 10 • 15 •

doUars damag!! to the sout h part o f the ci ty (Bcrtolane, 1985). September 2nd a lso saw hail up to the si7.e ofb::tseballs and several oth er smalllOrnadoes to the west and northwest o f London. Hail. damaging winds or fl ooding rains were also reponed in the London area on three days in each of the months of June, July and August.

TIlC Hamilton area expericnced a stormy period in mid June. Severe thunderstorms on June 13th and June 18th caused two lightning deaths and major damage duc to flooding.

A tornado struck the north patt of ToronLo on August 14th causing millions of dollars d:lmage. This Morm was very unusual in Ihal it moved from the no rtheast to the southwest. an almosl unheard-of event in tornado st'll is lics.

There were a few o ther storms of note. The Westport tornado on

50 Climatological Bulletin I Uulletin climato[ogique 21( 1) 1987

June 18th (Voak el. at., 1984) severely damaged a. small group of buildings JUS!

outside that ea<;tl:rn Ontario town. On July 6th scverultormu..locs were reporled across southwestern and centra l Ontario. The most noteworthy of these storms badly damaged a townhouse unit in Elora.

4.5 The Quebec Region (southellstcm Ontario, Quebec) Confirmed severe storms occurred on 29 days during the 1984 se.:lson which began on May 12th, and ended on October 3rd. Flooding downpours were particu larly co mmon . In the second half of August some regions such as Pontiac, Gatineau and Laurentian wert' inundated four times wit hin two weeks by rainfalls in the 50 to 100 mm rangc. The Pontiac and Gatincau regions were also struck by tornadoes all July 15th when cottages were flattened, other buildings damaged and at least 38 people injured by flyi ng c,lebris (Allen, 1984). At Blue Sea Lake, a woman was killed. On August 3rd, another fatal ity was sull"ered when lightning sl ruck and killed an individual at G ranby. Other dramatic events indude May 23rd when severe thunderstorms caused considerable damage Ileaf Riviere-du-Loup, June 18th when partS uf Montreal were nooded, and ..Iuly 6th when damaging wi nds, large hail and noodlng downpours ravaged parts of the Eastern Townships, near Sherbrooke.

Rl!rERENCES

Allen, D.E., 1984: l brnado Damage al Blue Sea Lake and Nicabong, Qul!bec, July 1984. Building Research Note 222, NRC, Ottawa.

Bertolone, L., 1985: Labour Day Weekend Tornado at London, Ontario. Chinook, Vol. 7. No.4, PI'. 58-txt

Leduc, M., 1984: The Ontario Weather Centre Summ~r Severe Weuthcr Season and Program, 1984. ORTN-84-8, Omario Weather Centre. AES, Toronto.

1 .~V I , I .. , 11)84: The t984 Prairie Weather Cenlre SU lnJUt'r Severe Wetull"r Reporl. Internal Report , Prairie Weather Centre, AES. Winnipeg,

Letchrord. r ., O. Waugh "nd A. Wallace, 1984: Report on the 1984 Summer Severe Weather Season in Alberta and NOrlh~slem British Columbia. Internal Repon , Albert Weather Centre, AES, Edmonton.

Newark, M.J., 1983: Tornadoes in Canada for the Period 1950-1979. CLl-2-S3, AES, Down~view.

Siok, S., 1984: 1984 Quebec Region Summer Severe Wc.,ther Seru;on. RTRQ-85R-OOI, Centre meteorologique du Quebec, AES, Montreal.

Voal: , R.E., Leduc, M.J. , and P. Stuart, 1984: Investigation or Tornado at Westport Ontario on Jtlne 18, 1984. ORTN-S4-6, Ontario Weather Centre, AES, Toronto.

M.i. Newark et af. / 1984 Severe Local StOrm Season 51

News and Comments Nouvelles et commentaires

ALBERTA CLIMATOLOGICAL ASSOCIATION ANNUAL MEETING

The 11th Annual Meeting of the ACA is scheduled for February 24,1987. This year, the meeting will be held at the Northern Forest Research Centre in Edmonton. The theme of the technical session will be Current Activities in Applied Climatology.

CLIMATE CHANGE INFORMATION

Henry Hengeveld CO,/Climate Advisor Canadian Climate Centre

Climate change, and man's possible role as a perpetrator of such change, has been a major scientific concern within the international research community for more than a decade. It still is today! Related research to remove the large uncertainties that still remain arid to better define its implications for society are by necessity resulting in unprecedented levels of cooperation and interaction between the various disciplines of the physical sciences, particularly at their interfaces. The Canadian research community continues to be an active participant in this research.

Several years ago, in order to stay abreast of developments in the above international research and to keep Canadian decision makers advised, the Canadian Climate Centre of the Atmospheric Environment Service initiated an advisory service on changing atmospheric chemical composition and climate. Financially assisted by the national Energy Research and Development program (administered by the federal Department of Energy, Mines and Resources), this service attempts to assimilate recent results of related research activities and transfer this information to the broader Canadian scientific and policy-making communities and to the general

52 Climatological Bulletin / Bulletin c1imatologique 20(2) 1986

Canadian public through newsletters, annual reports, consultations and briefings. One of the information products issued as part of this program is a periodic (3-4 times/year) newsletter, the "CO,/Climate Report," which attempts to update readers on recent developments in related research activities and results. In addition an annual report entitled "Understanding CO, and Climate," which tries to summarize the current status of understanding of this subject within the international scientific community, is released in the spring or early summer of each year.

Readers can arrange to be included on the mailing list for the above reports, which ate disseminated free-of-charge, by contacting the CO,/ Climate Advisor, Mr. Henry Hengeveld, at the Canadian Climate Centre, 4905 Dufferin Street, Downsview, Ontario, M3H 5T4. Mr. Hengeveld is also available for consultation and as a source for additional information. He can be reached at (416) 667-4525.

SASKATCHEWAN CLIMATE ADVISORY COMMITTEE

Ken Jones Secretary Saskatchewan Climate Advisory Committee

The SCAC held its third annual workshop in October 1986. The workshop took place in the new confines of the National Hydrological Research Centre in Saskatoon. The general theme of the workshop was "Computer Applications of Climate data." Ten preser:ltations were made covering a wide range of applications, varying from how to access the AS-9 in the Canadian Climate Centre to modelling snow drifting and melt. A tour of the new NHRC facilities followed the workshop.

Another major activity of the SCAC this year involved the initializing of a study regarding "The Feasibility of a Saskatchewan Climate Centre." Progress has been slow but the funds have now been acquired to proceed with this study.

ACFAS ANNUAL CONFERENCE

The 54th conference of the "Association Canadienne Franc;aise pour l'Avancement des Sciences" (ACFAS) will be held on 19-22 May, 1987, at the University of Ottawa. The main theme of the meteorology and climatology sessions will be "The Impact of Climatic Change." Roger Barry (Colorado and NCAR) will give a presentation on "Impacts of Climate Change on Snow and lee Conditions in the Arctic."

Other sessions will include papers on air pollution, physical and

News and Comments / Nouvelles et commentaires 53

dynamic meteorology/climatology, statistical climatology, agroclimatology, paleoclimatology, urban climatology, and remote sensing applications. Simultaneous translation will be provided.

The deadline date for abstracts was 15 January 1987. For more information, contact:

54

Alain Viau Climatology and Meteorology division co-ordinator c/o Universite de Montreal 2730, chemin de la Cote-Ste-Catherine Montreal, Quebec H3T 1B7 (514-342-1411)

Climatological Bulletin / Bulletin climatologique 20(2) 1986