Seasonal Forecast Updated: 6/28/17

Size: px

Start display at page:

Download "Seasonal Forecast Updated: 6/28/17"

Dinah Webb
5 years ago
Views:

1 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 named storms, 5-7 hurricanes, and 2-3 major hurricanes are expected for the entire hurricane season this year. 1

2 Monthly and Seasonal CDD Tables Seasonal Forecast Observed and Forecast U.S. Population Weighted CDDs and Percent of 30 Year Avg Month Obs/Forecast Previous Fcst* Fcst Change Last Year 5YR Avg Normal Mar (185.5%) 37 (185.5%) 0 (0%) 33 (162.5%) 27 (135%) 20 Apr (155.1%) 79 (155.1%) 0 (0%) 57 (111.4%) 59 (115.7%) 51 May (103.9%) 138 (103.9%) 0 (0%) 133 (100.2%) 154 (115.8%) 133 Jun (109.7%) 313 (116.3%) -18 (-6.6%) 320 (118.8%) 299 (111.2%) 269 Jul (106.7%) 394 (103.5%) 12 (3.2%) 443 (116.2%) 409 (107.3%) 381 Aug (105.3%) 369 (103.5%) 6 (1.7%) 419 (117.8%) 375 (105.3%) 356 Sep (104.6%) 213 (102.7%) 4 (1.9%) 270 (130.2%) 245 (118.4%) 207 Oct (97.3%) 74 (95.5%) 1 (1.8%) 111 (144.2%) 93 (120.8%) 77 Nov (75.7%) 16 (77.1%) 0 (-1.4%) 33 (154.8%) 24 (114.3%) 21 Mar May (124.7%) 254 (124.7%) 0 (0%) 223 (109.1%) 243 (119.1%) 204 Jun Aug (107.1%) 1076 (107%) 1 (0.1%) 1182 (117.6%) 1083 (107.8%) 1005 Sep Nov (100.8%) 302 (99.1%) 5 (1.7%) 413 (135.4%) 362 (118.7%) 305 May Sep (106.3%) 1426 (106%) 5 (0.3%) 1585 (117.7%) 1482 (110.1%) 1346 *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 Month Obs/Forecast Previous Fcst* Fcst Change Last Year 5YR Avg Normal Mar (168.3%) 66 (168.3%) 0 (0%) 61 (157.3%) 50 (128.2%) 39 Apr (146.5%) 120 (146.5%) 0 (0%) 94 (114.4%) 100 (122%) 82 May (106.6%) 197 (106.6%) 0 (0%) 182 (98.1%) 203 (109.7%) 185 Jun (108%) 358 (112.6%) -15 (-4.6%) 369 (116%) 349 (109.7%) 318 Jul (106.6%) 437 (103.6%) 13 (3%) 486 (115.2%) 447 (105.9%) 422 Aug (105.8%) 425 (104.5%) 5 (1.3%) 455 (111.8%) 428 (105.2%) 407 Sep (105.9%) 280 (104.2%) 5 (1.7%) 330 (122.5%) 309 (114.9%) 269 Oct (103%) 128 (101.2%) 2 (1.8%) 168 (133.1%) 149 (118.3%) 126 Nov (82%) 37 (82.6%) 0 (-0.6%) 59 (132%) 48 (106.7%) 45 Mar May (124.8%) 383 (124.8%) 0 (0%) 337 (109.7%) 356 (116%) 307 Jun Aug (106.7%) 1220 (106.4%) 3 (0.3%) 1310 (114.2%) 1224 (106.7%) 1147 Sep Nov (102.9%) 445 (101.4%) 7 (1.5%) 557 (126.8%) 506 (115.3%) 439 May Sep (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. 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. 2

June 2017 Anomaly Projections and 2017 Cooling Season-to-Date June 2017 Temperature Anomaly Projections June 2017 Precipitation Anomaly Projections Pop Weighted CDDs Rank Year CDDs 1 2012 569 2 2017

2004 480 20 1990 475 21 2009 469 22 1998 468 23 2001 464 24 1988 440 25 1999 424 26 1995 423 27 2005 420 28 1993 411 29 2003 394 30 1997 390 31 1992 387 Expected CDDs in 15 Days Rank Year CDDs 1 2012

3 June 2017 Anomaly Projections and 2017 Cooling Season-to-Date June 2017 Temperature Anomaly Projections June 2017 Precipitation Anomaly Projections Pop Weighted CDDs Rank Year CDDs Median Expected CDDs in 15 Days Rank Year CDDs Median

ENSO Update Seasonal Forecast Warmer than normal water has expanded some across the central tropical Pacific during the last couple weeks, and the Niño 3.

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.

4 ENSO Update Seasonal Forecast 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 El Niño continues to dissipate. Current SST Anomalies (Left), from two weeks ago (Right) and from last year (bottom) 4

4 region of the central equatorial Pacific is the region most commonly used to classify the strength of ENSO events.

5 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) 5

Summer Ag Weather Impacts Seasonal Forecast Soil moisture conditions have a significant impact on temperature anomaly patterns during the middle of summer.

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.

6 Summer Ag Weather Impacts Seasonal Forecast 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 midsummer 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 6

7 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. 7

8 Cumulative CDD Anomaly 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 May 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 8-May 15-May 22-May 29-May 5-Jun 12-Jun 19-Jun 26-Jun 3-Jul 10-Jul 17-Jul 24-Jul 31-Jul 7-Aug 14-Aug 21-Aug 28-Aug 4-Sep 11-Sep 18-Sep 25-Sep 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. April September Forecast Water Supply (Percent of Normal) Frontier Last Last 5 Year 10 Year Dam Location Forecast Forecast Year Average Average 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% January July Forecast Water Supply (Percent of Normal) Frontier Last Last 5 Year 10 Year Dam Location Forecast Forecast Year Average Average 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% 8

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,

9 2017 Hurricane Season Update Seasonal Forecast 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 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. 9

US Hurricane Landfall Return Periods by County ENSO Phase* Named Storms Hurricanes Major Hurricanes Number Years Last Year (Weak La Niña) 15 7 4 1 All Years Since 1950 4-11 - 28 2-6 - 15 0-3 - 8 67

10 US Hurricane Landfall Return Periods by County ENSO Phase* Named Storms Hurricanes Major Hurricanes Number Years Last Year (Weak La Niña) All Years Since All Years Since Moderate-Strong El Niño All El Niño since All El Niño since Neutral ENSO since Neutral ENSO since All La Niña since All La Niña since Moderate-Strong La Niña *Per CPC ONI methodology -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 10

11 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 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,

12 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 12

13 Early Winter Temperature ( F) and Precipitation (in) Anomaly Outlook Previous Winter Temperature and Precipitation Outlook 13

14 Monthly Temperature Anomaly Forecasts Seasonal Forecast Current Forecast Previous Forecast Last Year Five Year Average 14

15 Monthly Precipitation Anomaly Forecasts Seasonal Forecast Current Forecast Previous Forecast Last Year Five Year Average 15

16 Long Range Natural Gas Storage Projections Seasonal Forecast 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. 16

Europe Outlook July is now forecast to average close to

normal in July while southern areas are drier.

upcoming fall season looks to average at or above normal

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

17 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. 17

18 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) 18

19 References CSU hurricane season forecast: ENSO model composite from IRI: Climate models from IRI: JAMSTEC model: UKMET model: CFS Climate model: Stratospheric Optical Depth: Rutgers Snow Lab: MEI index: Arctic temperature graphs from DMI: Sea ice maps and graphs from NSIDC: NCDC USHCN Data: CPC ENSO Data: Map plotting tools: PDO Index: AER AO blog: Stratospheric analysis plots: 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. 19

MORNING WEATHER SUMMARY

MORNING WEATHER SUMMARY Weather Headlines Hot weather will prevail across the West into next week while another shot of cooler air moves into the eastern US. The 6-10 day period was trended slightly warmer