ALCA - Home - Part I: Synoptic–Scale Composite Map · 2011-08-31 · Lab 12 Answer Key...
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Explorations in Meteorology 54 Lab 12 Answer Key ANSWER KEY Part I: Synoptic–Scale Composite Map 1. Using Figure 2, locate and highlight, with a black dashed line, the 500-mb trough axis. Also, locate and highlight, with a black zigzag line, the 500-mb ridge axis located downstream from the trough. Transpose both of these axes to Figure 3 –– your synoptic-scale composite chart.
Transcript of ALCA - Home - Part I: Synoptic–Scale Composite Map · 2011-08-31 · Lab 12 Answer Key...
Explorations in Meteorology 54 Lab 12 Answer Key
ANSWER KEYPart I: Synoptic–Scale Composite Map
1. UsingFigure2, locateandhighlight,withablackdashed line, the500-mb troughaxis.Also, locateandhighlight,withablackzigzagline,the500-mbridgeaxislocateddownstreamfromthetrough.TransposebothoftheseaxestoFigure3––yoursynoptic-scalecompositechart.
Explorations in Meteorology 55 Lab 12 Answer Key
Figure 3 – Synoptic–Scale Composite Chart Valid at 1200 UTC on 2 April 1994
Explorations in Meteorology 56 Lab 12 Answer Key
2. Theareabetweentheaxesofanupper-leveltroughandthenextdownstreamridgeoftenisapreferredregionforlarge-scalerisingmotion.Outlinethisareaonyourcompositechart(Figure3)usingabluepencil.
3. Examinethe850-mbtemperaturefieldonFigure4andthesoundingdatainTable1.Inashortparagraph,describethetemperaturepatternat850mboverwesternOklahoma,theTexasPanhandle,andsouthwestTexas.Includeanswerstothefollowingquestionsinyourparagraph:
(a) Arethetemperaturesat850mbinthisarearelativelywarmorrelativelycool?(b) Howdothetemperatureschangewithheightoverthisarea(i.e.,dotheyincreaseordecreasewith
height)?(c) Isthistemperaturechangewithheightastableorunstableconfiguration?(d) Baseduponthewindandmoisturedata(Table1),fromwheredidtheairat850mbinthisregion
likelycome?(Hint:Youmaywanttocomparethe850-mbtemperaturesandwindswiththesurfacetemperaturesandwinds.YoualsomaywanttocalculatethetemperaturechangewithheightfromthesoundingdatainTable1.)
At850mb,warmairwaspresentoverwesternOklahomaandtheTexasPanhandletotheTexas-MexicoborderbetweenElPasoandtheBigBend.ThisareahadthewarmestairovertheUnitedStatesatthisanalysistime.These850-mbtemperatureswereconsiderablywarmer thancorrespondingsurface temperatures;hence,asignificant temperatureincreasewithheightoccurredacross thisarea.Forexample, thesurface temperaturesatAmarillo,TXandMidland,TXwereabout~8-9ºCcooler than theirassociated850-mb temperatures.Thus, thisareawascoveredbyastronginversion,alsoknownasa“cap”,whichisastablepattern.
Thewarmairat850mbalsowasverydry.Surfacedewpointswere3.5ºClessthanthecorrespondingtemperatures,whereas850mbdewpointdepressionswere20-30ºC.Becauseofthedrynessoftheairat850mbandthesoutherlycomponentofthewinds,theairatthislevellikelycamefromthearidregionknownastheMexicanPlateau.
4. Onyourcompositechart(Figure3),outlineinredthesignificanttemperaturepatterndiscussedinquestion3.(Hint:Youmaywanttosketcha15°Cor16°Cisothermtorepresentthe patterninthiscase.)
SeeFigure3(compositechart).
5. Examinethe850-mbdewpointdepressionmaps(Figures5and6).Comparethemoisturepatternat1200UTCon2April1994(Figure5)withtheone12hourslaterat0000UTCon3April(Figure6).WhathappenedtothemoistureoverOklahomaandTexas?Scallopingreenthelocationofthesignificantmoistureat850mbat1200UTConyourcompositechart(Figure3).Useagreenarrowtodenotethemovementofthemoistestair(alsoknownasamoisturetongue)duringthefollowing12-hourperiod(to0000UTCon3April).
AbundantmoistureadvectednorthwardovereasternTexasandeasternOklahomafromsouthernTexasandtheGulfofMexicoduringthe12-hourperiod.DewpointdepressionsdecreasedovercentralOklahomafrom25ºCto7ºC,while2ºCdewpointdepressionswereascloseasnortheasternTexas.Strongsoutherlywindsprevailedacrosstheentireareaofsignificantmoistureadvection.
6. ExaminetheSkew-TdiagramsforNorman,OK(OUN)at1200UTCon2April1994(Figure7)and0000UTCon3April1994(Figure8).Onthemorningsounding,describethestructureofthetemperatureplotbeneath500 mb. List the levels where the temperature decreases with height and the layers where temperatureincreaseswithheight.Whatisthetechnicalnameforthesignificantfeatureorpatternbelow850mb?
Layer(s)wheretemperaturedecreaseswithheightat1200UTCFrom850mbto500mb(andhigher)
Layer(s)wheretemperatureincreaseswithheightat1200UTCFromthesurfaceto850mb
Nameoffeaturebelow850mbat1200UTC Aninversion
Explorations in Meteorology 57 Lab 12 Answer Key
7. (Advanced Students/Meteorology Majors)Does the temperaturepatternbelow850mbaidoropposestormdevelopment?Explainyouranswer.
Theinversionpreventsstormsfromformingimmediatelybecauseitpreventssurfaceairparcelsfromrisingtoformdeep,thunderstormclouds.However,someamountofinversionisnecessarytokeepthesurfaceinstabilityconfinedsothatexplosivedevelopmentcouldoccurlater.Thus,theinversioncanbeapositivefactorforthunderstormdevelopment.Sometimes,otherfactorsexistandovercometheinversion.
8. Lookat thewindson themorningsounding (Figure7).Commentonhowthewindsspeedanddirectionchangewithheight.Often,meteorologistsconsider500-mbwindstobethesteeringcurrentsforstorms.Basedonthisconcept,whatdirectionshouldthestormsmoveacrosscentralOklahomaontheafternoonon2April1994?Toindicateyourforecastedstormmotion,plotandlabelabluearrowonyourcompositemapacrosscentralOklahoma.
ForecasteddirectionofstormmovementacrosscentralOK-Westtoeast.Thewindsbasicallyincreasedinspeedwithheight.Theyalsoturnedfromsoutherlyatthesurface,tosouthwesterlyupto850mb,andwesterlyabove850mb.The500-mbwindswerewesterly.
9. Compare the morning sounding (Figure 7) to the evening sounding (Figure 8). Describe how the windschanged,ingeneral,throughouttheday.
Thewinds increased in speedatnearly all levels from themorning to theeveningsounding,perhaps indicatinganincreasingintensityofthestormsystemasitorganizedoverOklahoma.Thesurfacewindschangedduringthedaytobesoutheasterly,indicatingthatmoremoistureadvectedintocentralOklahoma(e.g.,Normansurfacedewpointincreasedfrom9°Cto13°C).
Part II: Mesoscale Composite Map
County-leveldatafromtheOklahomaMesonet(www.mesonet.org)wasavailableforthemesoscaleanalysison2April1994.Mesonetmapsaredisplayedinlocaltime.YoumaywanttorefertothemapofOklahomacountiesinFigure9tousecountynamesinyouranswerstothequestionsthatfollow.
10. Examinethetemperature,dewpoint,andwinddatafor2:30PMCSTon2April1994(Figures10,11,and12).Identifyany fronts,drylines,andhigh-or low-pressurecentersusing thecustomarysymbolsandcolors.Transposethosesymbolsontoyourmesoscalecompositemap(Figure13).
Figure 10 – Temperature (in °F) for 2 April 1994 at 2:30 PM CST (2030 UTC), as Measured by the Oklahoma Mesonet
Explorations in Meteorology 58 Lab 12 Answer Key
Figure 11 – Dew Point (in °F) for 2 April 1994 at 2:30 PM CST (2030 UTC), as Measured by the Oklahoma Mesonet
Figure 12 – Winds Speed (in kts) and Direction for 2 April 1994at 2:30 PM CST (2030 UTC), as Measured by the Oklahoma Mesonet
Explorations in Meteorology 59 Lab 12 Answer Key
11. UsingFigure10,identifythelocationofthewarmestair(alsoknownasathermalridge).Shadethiswarmairregioninredpencilonyourmesoscalecompositemap(Figure13).[Hint:Tobestidentifythisfeature,youmaywanttolocateandsketchanisotherminthe80º–83ºFrange.]
SeeFigure13(compositechart).
12. UsingFigure11,identifythelocationofthemoisturetongue.Drawagreenscallopedlinearoundthismoistair regiononyourmesoscalecompositemap(Figure13).Shadetheareawithinthescalloped linewithagreenpencil.[Hint:Tobestidentifythisfeature,youmaywanttolocateandsketchthe55ºFisodrosotherm.Surface dewpoint temperatures in the mid-50s often are considered as the threshold needed for severestormdevelopment.]
13. Inspect thebase reflectivity image from2:42PMCST (2042UTC)shownbyFigure14.At this time, theNEXRADradarwasoperatinginclear-airmode ––averysensitiveconfigurationusedtodetectatmosphericboundariessuchasfrontsordrylines.Inclear-airmode,theradardetectschangesinatmosphericdensity,typicallyresultingfromeithertemperatureormoisturegradients.Whentwodissimilarairmassesareadjacent,adiscontinuityinatmosphericdensitymayshowupasa thinlineontheradardisplay.
OnFigure14,athinlineisevidenttothewestoftheradar’slocation(nearOklahomaCity).HowdoesthethinlinecorrespondwithpatternsobservedbytheOklahomaMesonet(Figures10,11,and12)?
ThethinlineoverKiowa,Caddo,andBlainecountieswasassociatedwiththedryline.
Figure 13 – Mesoscale Composite Chart Valid at 2:30 PM (2030 UTC) on 2 April 1994
Thepreferredareaforstormdevelopmentisgenerallyeastofthedryline(inthemoisttongue)andnearthethermalridge.Thislocationmaximizessurfaceinstability(i.e.,theareathatisthewarmestandmostmoist)whichacttohelpovercomeanycap.
Explorations in Meteorology 60 Lab 12 Answer Key
Describethedensitydifferencesbetweenthewestandeastsidesofthethinline(i.e., Istheatmosphericdensityhigherorloweronthewestsideascomparedtotheeast?).Howdidyouarriveatyouranswer?
Thewestsideofthedrylinewashotanddry,whiletheeastsidewaswarmandmoist.Watervapormoleculeshavelessmassthandoairmolecules.Thus,moistairislessdensethandryairandcausesthedrylinetoshowupasadensitydiscontinuitybetweenthemoredensehot,dryaironthewestsideandthe lessdensewarm,moistairontheeastside.
Explainwhyweatherradarmayhaveanadvantageoveranetworkofsurfaceweatherstationsindetectingtheselow-leveldiscontinuities.
Theradarhasoneprimaryadvantagecomparedtoasurface-basedmesonet:itcandetectthelocationofthedrylinewithhigherresolution,mostlyinspacebutsometimesalsointime(e.g.,6-minuteupdates).
14. By 2:30 PM CST, thunderstorms had not developed in Oklahoma. Using both your knowledge of theenvironmentrepresentedbyyourcompositecharts(Figures3and13)andyourknowledgeoftheingredientsnecessaryforthunderstormdevelopment,wherewillthunderstormsmostlikelydevelopfirst?Outlineyourforecastedareaofseveralcounties(~5-10)inblackonyourmesoscalecompositechart(Figure13)whereyouthinkthestormswillform.
Countieswherestormswillforminitially(Note:CountynamesareonFigure9.)Jefferson,Cotton,Stephens,Comanche,Caddo,Grady,Canadian,Blaine,andKingfisher.SeeFigure13(compositechart).
15. Whenyoufinishyourlab,yourinstructorwillshowyouaradarloopofthebasereflectivity(inprecipitationmode) from3:15PMto8:00PMCST.Use this information toverifyqualitativelyyour forecastsofstormdevelopmentandmotion.Describehowwellyouforecastedthestormmotion(question8)andthelocation(s)ofstorminitiation(question14).Ifyoudidnotforecasttheeventwell,whatadditionalinformationmayhavehelpedyoutomakeabetterforecast?
ThegeneralflowoftheechoeswasfromwesttoeastacrossOklahoma,agreeingwiththeforecastedstormmotion.
16. (Advanced Students/Meteorology Majors) Usetheradarloop(displayedbyyourinstructor)tocommentontheevolutionandmotionofthestormsthatformedinbothComancheCountyandMajorCounty(seeFigure9forcountynames).Inconsideringyouranswer,comparethemotionofthesetwostormswiththemotionofotherstormsacrossOklahoma.
Afewconvectivecellsdeviatedfromthegeneralflow.ThestormthatformedinMajorCountyturnedtothesoutheast;itbecamearight-movingstorm.ThestorminComancheCountysplitintotwostorms.First,onestormfromthesplitmadeaslight turn to theright (i.e.,southeastward).ThisstormpassedthroughPontotocCountyandproducedhaildamagethere.Thesecondstormfromthesplitturnedtothenorthward.Thisleft-movingstormeventuallymergedwiththenortherncomplexofstorms.Thisleft-moveralsoacceleratedandpersistedforanunusuallylongtimecomparedtomost“leftmoving”storms.
