Seasonal Forecast - Frontier Weather - DTN

Seasonal Forecast Updated: 6/28/17

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July Temperature (°F) and Precipitation (in) Anomaly Outlook

August Temperature (°F) and Precipitation (in) Anomaly Outlook

Fall Temperature (°F) and Precipitation (in/month) Anomaly Outlook

Forecast Headlines

• July is forecast to average warmer and drier than normal across most of the country, with the strongest warm anomalies across the West as well as the Northeast.

• Most of the country is forecast to average above normal during August as well, and the central US has been trended drier with any El Niño influence continuing to fade.

• The entire June-August period looks to end up nearly identical to the last forecast in terms of population weighted CDDs since the second half of June is ending up a little cooler than previously forecast and July and August are slightly warmer.

• 12-15 named storms, 5-7 hurricanes, and 2-3 major hurricanes are expected for the entire hurricane season this year.




Monthly and Seasonal CDD Tables

Month Obs/Forecast Previous Fcst* Fcst Change Last Year 5YR Avg NormalMar 2017 37 (185.5%) 37 (185.5%) 0 (0%) 33 (162.5%) 27 (135%) 20Apr 2017 79 (155.1%) 79 (155.1%) 0 (0%) 57 (111.4%) 59 (115.7%) 51May 2017 138 (103.9%) 138 (103.9%) 0 (0%) 133 (100.2%) 154 (115.8%) 133Jun 2017 295 (109.7%) 313 (116.3%) -18 (-6.6%) 320 (118.8%) 299 (111.2%) 269Jul 2017 406 (106.7%) 394 (103.5%) 12 (3.2%) 443 (116.2%) 409 (107.3%) 381

Aug 2017 375 (105.3%) 369 (103.5%) 6 (1.7%) 419 (117.8%) 375 (105.3%) 356Sep 2017 217 (104.6%) 213 (102.7%) 4 (1.9%) 270 (130.2%) 245 (118.4%) 207Oct 2017 75 (97.3%) 74 (95.5%) 1 (1.8%) 111 (144.2%) 93 (120.8%) 77Nov 2017 16 (75.7%) 16 (77.1%) 0 (-1.4%) 33 (154.8%) 24 (114.3%) 21

Mar 2017 - May 2017 254 (124.7%) 254 (124.7%) 0 (0%) 223 (109.1%) 243 (119.1%) 204Jun 2017 - Aug 2017 1076 (107.1%) 1076 (107%) 1 (0.1%) 1182 (117.6%) 1083 (107.8%) 1005Sep 2017 - Nov 2017 307 (100.8%) 302 (99.1%) 5 (1.7%) 413 (135.4%) 362 (118.7%) 305May 2017 - Sep 2017 1431 (106.3%) 1426 (106%) 5 (0.3%) 1585 (117.7%) 1482 (110.1%) 1346

Observed and Forecast U.S. Population Weighted CDDs and Percent of 30 Year Avg

*Previous forecast is from last seasonal update report. Values are updated daily on the Frontier Weather website.

Month Obs/Forecast Previous Fcst* Fcst Change Last Year 5YR Avg NormalMar 2017 66 (168.3%) 66 (168.3%) 0 (0%) 61 (157.3%) 50 (128.2%) 39Apr 2017 120 (146.5%) 120 (146.5%) 0 (0%) 94 (114.4%) 100 (122%) 82May 2017 197 (106.6%) 197 (106.6%) 0 (0%) 182 (98.1%) 203 (109.7%) 185Jun 2017 343 (108%) 358 (112.6%) -15 (-4.6%) 369 (116%) 349 (109.7%) 318Jul 2017 450 (106.6%) 437 (103.6%) 13 (3%) 486 (115.2%) 447 (105.9%) 422

Aug 2017 431 (105.8%) 425 (104.5%) 5 (1.3%) 455 (111.8%) 428 (105.2%) 407Sep 2017 285 (105.9%) 280 (104.2%) 5 (1.7%) 330 (122.5%) 309 (114.9%) 269Oct 2017 130 (103%) 128 (101.2%) 2 (1.8%) 168 (133.1%) 149 (118.3%) 126Nov 2017 37 (82%) 37 (82.6%) 0 (-0.6%) 59 (132%) 48 (106.7%) 45

Mar 2017 - May 2017 383 (124.8%) 383 (124.8%) 0 (0%) 337 (109.7%) 356 (116%) 307Jun 2017 - Aug 2017 1224 (106.7%) 1220 (106.4%) 3 (0.3%) 1310 (114.2%) 1224 (106.7%) 1147Sep 2017 - Nov 2017 452 (102.9%) 445 (101.4%) 7 (1.5%) 557 (126.8%) 506 (115.3%) 439May 2017 - Sep 2017 1706 (106.5%) 1698 (106.1%) 8 (0.5%) 1821 (113.8%) 1736 (108.4%) 1601*Previous forecast is from last seasonal update report. Values are updated daily on the Frontier Weather website.

Observed and Forecast U.S. %AC X %NG Generation Weighted CDDs and Percent of 30 Year Avg

The %AC x %NG generation weighted CDDs weight the CDD totals for each state by a combination of the percent of the households that have air conditioning and the percent of electricity that is produced from power plants fueled by natural gas.




June 2017 Anomaly Projections and 2017 Cooling Season-to-Date

June 2017 Temperature Anomaly Projections

June 2017 Precipitation Anomaly Projections

2012 569

Pop Weighted CDDs

2017

CDDsRank

2

Year

5503 2015 543

YearRank1

CDDs1

7 2016 5248 1994

21

15 2000

19 2004

5424 1991

6 2010 5245 2011 541

48020 1990 475

5069 2006 50010

485

17 1996 482Median 1989 482

8

13

1987 49612 2014 491

496

49014 2008 48913 2002

2007

18 2013

11

1994 69576 2016 708

2015 707

1991 7342010 713

3

54

2012 8002 2017 747

2011 745

1987 67014 1990 669

2006 67412 2014 67311

2002 68210 2013 6759

631

19 1998 64520 2000 641

17 1989 65918 1996 647

15 2007 6692008 662Median

1997 545

Expected CDDs in 15 Days

29 2003 57230 1992 549

27 2005 59728 1995 581

25 1993 61126 1999 606

23 2009 62124 1988 615

21 2004 63522 2001

387

1993 41129 2003 39430 1997 390

2009 469

1988 440

27 2005

481

31

42028

26 1995 423

23 2001 4642425 1999 424

22 1998 468

199231




ENSO Update

Warmer than normal water has expanded some across the central tropical Pacific during the last couple weeks, and the Niño 3.4 region anomalies have moved back above the +0.5°C El Niño threshold. Sub-surface water temperatures have also warmed a bit, so conditions look to remain solidly in the “warm neutral” to borderline weak El Niño range for the balance of the summer season. However, while the central Pacific has trended warmer, the eastern Pacific continues to remain closer to normal and conditions don’t currently look to support much warming in that region. The eastern Pacific water temperatures can have a larger impact on US weather in the summer, and so the cooler conditions there relative to a couple months ago still favors a warmer and drier central US for the balance of the summer than forecast back in March and April. Warmer water in that region tends to promote more tropical convection, including hurricanes, which in turn help to send periodic bursts of moisture up into the Southwest and out across the Plains at higher levels of the atmosphere. That in turn helps to increase rainfall in those areas and suppress temperatures a bit. Since the eastern Pacific is now cooler, that looks to be less of a factor going forward. As a result, the forecast for the balance of the summer continues to trend warmer and drier across the middle of the country. The maps below show the current global SST anomalies on the left, and those from a couple weeks ago on the right. A map from roughly the same period last year is also included below for reference. Note that, in general, there is less warmth in the Pacific than this time last year as the residual warmth from the strong 2015-2016 El Niño continues to dissipate.

Current SST Anomalies (Left), from two weeks ago (Right) and from last year (bottom)




The following plots show time series of temperature anomalies for four regions of the equatorial Pacific. Niño 4 is in the western equatorial Pacific, and Niño 1+2 is located off the coast of South America. The Niño 3.4 region of the central equatorial Pacific is the region most commonly used to classify the strength of ENSO events. A plot of sub-surface water temperature anomalies is also shown and while there are pockets of warmer than normal water below the surface, no strong and widespread warm anomalies are present like you would normally see prior to a significant El Niño event. The latest composite of climate models is shown on the bottom right, and the general model consensus keeps the Niño 3.4 region in the warm neutral range, just below the El Niño cutoff of +0.5°C right on through the upcoming winter. Note that some model solutions still show weak El Niño development though, so the recent trend towards slightly warmer water in the central Pacific will need to be monitored in case it persists and/or strengthens during the next few months.

El Niño Region SST Trends (NCEP/CPC) and CFS Model Composite (bottom right)




Summer Ag Weather Impacts

Soil moisture conditions have a significant impact on temperature anomaly patterns during the middle of summer. Unlike in winter when cold airmasses spread southward into the US out of northern Canada when favorable blocking patterns develop, hot weather in the summer develops over the US itself. Upper level ridges often build across the Southwest early in summer, and then periodically expand northeastward across the country, spreading surges of hot weather eastward. How much heat is seen across the Plains and Midwest often depends on how wet or dry the soil conditions are as dry soil will heat up much faster than will saturated ground. When the ground is wet, much of the incoming solar radiation is used up evaporating water instead of warming the ground, which in turn keeps the air cooler. When the soil is dry, most of the incoming solar energy can go directly to warming the ground, which can then radiate heat into the air. That process may be overwhelmed by cooler Canadian air masses moving in, but during times when ridges expand across the central US dry soil conditions can help temperatures heat up rapidly. Strong upper level ridges often develop across the south-central US during mid-summer as conditions trend drier and the southwestern US ridge weakens with the onset of the seasonal monsoon there. The expansion and contraction of that upper level ridge often modulates temperatures across much of the central and eastern US during July and the first half of August. The East Coast can see their hottest and muggiest weather when the Bermuda High expands westward, which builds a hot upper level ridge across the region and helps increase moisture transport out of the Gulf of Mexico. After a very wet spring season, conditions have turned markedly drier across the central US. The map on the left below shows the rainfall anomalies over the last month or so, and the Plains region has trended much drier. There hasn’t yet been a significant temperature impact because conditions were so wet across much of the region this spring. The latest 15-day precipitation anomaly forecast from the GFS model shows that much of the country may end up drier than normal during the first half of July, with only modest positive rainfall anomalies across portions of the Midwest. So, in general the trend towards drier weather may continue, which in turn could favor a hotter second half of July and first half of August, possibly more so than currently forecast.

Rainfall Anomalies Last 30 Days Rainfall Anomalies Next 15 Days

The crop moisture index map on the next page shows that most of the Plains and Midwest still have average soil moisture, but that will change quickly with any persistence of drier weather since most of the soil moisture surplus from this spring has now been used up. Also, note that




while the Southeast had been drier than normal much of this year, TS Cindy quickly erased that moisture deficit and has now resulted in a surplus of soil moisture across the region. That may in turn help to keep humidity levels higher across the region in July and feed more of the typical afternoon showers and storms that are often seen across that region during mid-summer.

Summer Population Weighted CDD Outlook

On page 2 of this report, the CDD forecast tables show that we expect population weighted CDD totals to end up in the 6-7% above normal range for both the June-August and May-September periods. This is quite a bit below the 17-18% above normal totals seen last year and below the five-year average as well. However, as mentioned earlier, there is some risk that temperatures could end up a little hotter later in July and early in August because of the cooling eastern Pacific and generally drier central US pattern. The plot on the next page shows some population weighted CDD projections based on prior years data. Each line represents the balance of summer observed CDDs from each of the last 30 years appended onto the season-to-date total. Some ENSO composites are also shown along with last year’s values. Note that the composite of El Niño years shows that CDD anomaly totals often trend lower late in summer, while those from La Nina years often trend higher. The current forecast (black line) is still lower than the 10-year average curve, but there is risk for further increases in the CDD outlook. In any event, odds are increasing that the summer season will end up with moderately positive CDD anomalies, and the risk for the summer to end up with at or below normal in terms of population weighted CDDs continues to decrease.




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May - Sept 2017 US Population Weighted CDD Anomaly Plume (vs 30 Year Avg)

Current + 15 Day Fcst + Moderate-Strong El Nino

Current + 15 Day Fcst + Weak-Moderate El Nino

Current + 15 Day Fcst + Moderate-Strong La Nina

Current + 15 Day Fcst + Weak-Moderate La Nina

Current + 15 Day Fcst + Last Year

Current + 15 Day Fcst + 10 Year Average

Current + 15 Day Fcst + Forecast

56% of years warmer than Normal, 44% of years cooler than Normal when projecting end of season total using using observations to date plus weather from past years

Pacific Northwest Hydro Update

Streamflow forecasts have trended a bit lower across the Pacific Northwest since earlier this month. We are now past the normal peak in streamflows across the Northwest and flows should be falling of steadily during the remainder of the season. Even so, flow rates should remain above normal given the above normal snow packs still in place at high elevations.

Mica Dam (BC) 108% 113% 98% 108% 102%Grand Coulee 118% 121% 91% 105% 103%

The Dalles 127% 129% 88% 99% 102%Lower Granite 143% 143% 83% 84% 97%

Mica Dam (BC) 118% 125% 102% 111% 104%Grand Coulee 128% 130% 98% 108% 104%

The Dalles 137% 139% 97% 102% 102%Lower Granite 153% 154% 88% 87% 95%

April – September Forecast Water Supply (Percent of Normal)10 Year Average

Dam LocationFrontier Forecast

Last Forecast

Last Year

5 Year Average

10 Year Average

January – July Forecast Water Supply (Percent of Normal)

Dam LocationFrontier Forecast

Last Forecast

Last Year

5 Year Average




2017 Hurricane Season Update

Two named storms developed in the Atlantic basin since the last update, Bret and Cindy. Both were weak and short-live and didn’t add much to the seasonal ACE index total but have increased our storm count to three, which is solidly above normal for this time of year. With ENSO conditions looking to be more in the warm-neutral range, instead of fully into the El Niño range, and the eastern Pacific is cooler, odds favor at least near normal storm totals this year, and likely slightly above normal. However, the Atlantic has cooled slightly in the last couple of weeks as well, and the overall pattern isn’t as favorable for storms as in some recent years, so we still expect storm totals to be lower than last year. With three storms in the books, we have increased the bottom end of our seasonal forecast total to 12 from 11, though we have kept the top end of the forecast range at 15. This could end up being a year with far more named storms than hurricanes and it wouldn’t be surprising to see the number of named storms near the top end of the forecast range but the number of hurricanes near the lower end.

12-15 named storms (was 11-15) 5-7 hurricanes (was 5-7) 2-3 major hurricanes (was 2-3)

2017 Atlantic Storm Names

Arlene Harvey Ophelia Bret Irma Philippe

Cindy Jose Rina Don Katia Sean

Emily Lee Tammy Franklin Maria Vince

Gert Nate Whitney The plots below show the trends in storm numbers over time, as well as the frequency of storms by day of the year. Note that tropical activity, particularly hurricane frequency, doesn’t really ramp up until August.




US Hurricane Landfall Return Periods by County

ENSO Phase* Number YearsLast Year (Weak La Niña) 15 7 4 1

All Years Since 1950 4 - 11 - 28 2 - 6 - 15 0 - 3 - 8 67

All Years Since 1995 8 - 15 - 28 2 - 7 - 15 0 - 3 - 7 22

Moderate-Strong El Niño 6 - 8 - 11 2 - 4 - 8 0 - 2 - 5 9

All El Niño since 1950 6 - 9 - 18 2 - 5 - 12 0 - 2 - 6 19

All El Niño since 1995 8 - 11 - 15 3 - 5 - 9 1 - 3 - 6 6

Neutral ENSO since 1950 4 - 12 - 28 2 - 7 - 15 0 - 3 - 7 26

Neutral ENSO since 1995 8 - 16 - 28 2 - 8 - 15 0 - 4 - 7 8

All La Niña since 1950 5 - 13 - 19 3 - 7 - 12 1 - 3 - 8 22

All La Niña since 1995 12 - 16 - 19 5 - 8 - 12 1 - 4 - 5 8

Moderate-Strong La Niña 8 - 12 - 19 4 - 8 - 12 1 - 4 - 6 7*Per CPC ONI methodology

Named Storms Hurricanes Major Hurricanes

-All averages have been rounded to increase table readability. -Hurricane seasons have never (since 1950) seen more storms than normal with moderate to strong El Niño conditions. -Hurricane seasons have never (since 1995) seen less storms than normal with La Nina conditions in place




Forecast Summary

Our latest forecast maps are shown on the following pages. The June-August summer season looks to end up hotter than forecast in our last update across the West, but not quite as hot across the Midwest. The warmest anomalies for the balance of the summer season are expected to persist across the western US and along the East Coast, while the central US ends up more variable and averages a little closer to normal. No significant changes were made to the hurricane season outlook from the last update. Totals may end up a little higher than the long-term averages seen since 1950, but are likely to average at or below the 1995-2016 averages. Our outlook for the September-November fall season was trended a little warmer this update, again based on the increasing odds for a more persistent ENSO neutral regime and expected drier conditions across the central US. Portions of the central US were trended a bit cooler this update in the December-February winter outlook, but most of the country is still forecast to average at or above normal. However, it is still too early to have much confidence in the winter outlook. There has been a tendency for more persistent weather patterns during the winter season in recent decades, which has resulted in recent winters either averaging much colder than normal or at record or near record warm levels. With the entire Pacific basin generally cooler than the last couple of years with the residual El Niño warmth fading, a third straight record or near record warm winter is unlikely, but it is still highly uncertain whether temperatures will end up warmer than normal or if a return to the colder eastern US winters of a few years ago is in the offing.

The next full seasonal update report is scheduled for Wednesday, July 12th, 2017.




Latest Summer 2017 Temperature (°F) and Precipitation (in) Anomaly Projection

Previous Summer 2017 Temperature and Precipitation Projection

Forecast is the average monthly anomaly, not three-month total anomaly

Early Fall 2017 Temperature (°F) and Precipitation (in) Anomaly Outlook

Previous Fall 2017 Temperature and Precipitation Outlook




Early Winter 2017-18 Temperature (°F) and Precipitation (in) Anomaly Outlook

Previous Winter 2017-18 Temperature and Precipitation Outlook




Monthly Temperature Anomaly Forecasts

Current Forecast Previous Forecast Last Year Five Year Average




Monthly Precipitation Anomaly Forecasts

Current Forecast Previous Forecast Last Year Five Year Average




Long Range Natural Gas Storage Projections

The following plots show historical NG storage data for the last year, as well as an 8-month forecast. The top portion of the graph shows forecast storage levels, and the bottom portion the year on five-year surplus, along with the year on year surplus. The orange line represents the projected storage levels using the weekly five-year average storage numbers. Note that the forecast assumes no price response to production and demand levels, with forecast degree days being the only variable changing going forward. As such, large variations in storage levels from the mean may not actually develop, but may serve as an indicator that production, price and/or demand changes are likely.




Europe Outlook

July is now forecast to average close to normal across much of Europe, with central areas possibly a little below normal. A large swath of northern Europe may end up wetter than normal in July while southern areas are drier. August may trend warmer and drier central areas while the upcoming fall season looks to average at or above normal across most of the region in terms of temperatures along with near normal precipitation.

Europe July Temperature (°F) and Precipitation (in) Anomaly Outlook

Europe August Temperature (°F) and Precipitation (in) Anomaly Outlook

Europe Fall Temperature (F) and Precipitation Anomaly Outlooks (in/month)

Precipitation forecast shows average anomalies per month, not total anomaly.




Global July Temperature (°F) and Precipitation (in) Anomaly Outlook

Global August Temperature (°F) and Precipitation (in) Anomaly Outlook

Global Fall Temperature (F) and Precipitation Anomaly Projection (in/month)




References CSU hurricane season forecast: http://webcms.colostate.edu/tropical/media/sites/111/2017/04/2017-04.pdf ENSO model composite from IRI: http://iri.columbia.edu/our-expertise/climate/forecasts/enso/current/ Climate models from IRI: http://iri.columbia.edu/forecast/climate/all/sep14/all.djf15.2mt.n_america.html JAMSTEC model: http://www.jamstec.go.jp/frcgc/research/d1/iod/sintex_f1_forecast.html.en UKMET model: http://www.metoffice.gov.uk/research/climate/seasonal-to-decadal/gpc-outlooks/glob-seas-prob CFS Climate model: http://www.cpc.ncep.noaa.gov/products/people/wwang/cfsv2fcst/ Stratospheric Optical Depth: http://data.giss.nasa.gov/modelforce/strataer// Rutgers Snow Lab: http://climate.rutgers.edu/snowcover/index.php MEI index: http://www.esrl.noaa.gov/psd/enso/mei/index.html Arctic temperature graphs from DMI: http://ocean.dmi.dk/arctic/meant80n.uk.php Sea ice maps and graphs from NSIDC: http://nsidc.org/data/seaice_index/ NCDC USHCN Data: http://www.ncdc.noaa.gov/oa/climate/research/ushcn/ CPC ENSO Data: http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/enso.shtml Map plotting tools: http://www.esrl.noaa.gov/psd/cgi-bin/data/getpage.pl PDO Index: http://jisao.washington.edu/pdo/PDO.latest AER AO blog: http://www.aer.com/science-research/climate-weather/arctic-oscillation Stratospheric analysis plots: http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/ © 2017 WDT, Inc. All rights reserved. Any unauthorized reproduction, distribution or disclosure is prohibited and may result in account termination and/or prosecution. Information contained in this report is intended solely for use by the recipient and may not be further distributed without written approval from WDT, Inc. Users of this report agree to the following: THE REPORT is provided by WDT, INC “AS IS”, and “AS AVAILABLE” WITHOUT WARRANTY OF ANY KIND TO USER OR ANY THIRD PARTY, INCLUDING, BUT NOT LIMITED TO, ANY EXPRESS OR IMPLIED WARRANTIES OF MERCHANTABILITY OF THE REPORT; ACCURACY OF INFORMATIONAL CONTENT; NON-INFRINGEMENT; QUIET ENJOYMENT; AND TITLE. WDT, INC. SHALL NOT BE LIABLE FOR ANY LOSS, INJURY, CLAIM, LIABILITY OR DAMAGE OF ANY KIND RESULTING IN ANY WAY FROM THE USE OF THIS INFORMATION. THE USER FURTHER AGREES THAT WDT, INC. SHALL NOT BE LIABLE TO USER OR ANY THIRD PARTY FOR ANY LOSS OF PROFITS, LOSS OF USE, INTERRUPTION OF BUSINESS, OR ANY DIRECT, INDIRECT, SPECIAL, EXEMPLARY, INCIDENTAL OR CONSEQUENTIAL DAMAGES OF ANY KIND WHETHER UNDER THIS AGREEMENT OR OTHERWISE, EVEN IF WDT, INC. WAS ADVISED OF THE POSSIBILITY OF SUCH DAMAGES OR WAS GROSSLY NEGLIGENT. In any event, WDT, INC. shall never be liable for any amount in excess of the fees paid by the USER to WDT, INC. hereby. Additionally, WDT, INC. makes no warranty that the information provided in this report will be free from errors or omissions, or defects, human or mechanical.

Seasonal Forecast - Frontier Weather - DTN

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