Prognostic Discussion for Long-Lead Seasonal Outlooks NWS Climate Prediction Center College Park MD 830 AM EDT Thu Jun 18 2020 SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS The July-August-September (JAS) 2020 temperature outlook predicts likely above normal temperatures across Alaska and most of the contiguous U.S. (CONUS), with the exception being some areas near the Central Mississippi Valley, where equal chances (EC) of below, near and above normal temperatures are indicated. The JAS precipitation outlook predicts above normal precipitation to be likely for southern regions of Alaska, including the Aleutian Islands and the Alaska Panhandle. Above normal precipitation is also likely for much of the eastern CONUS from parts of the eastern Great Plains eastward across the Central and Lower Mississippi Valley to the Mid-Atlantic and Southeast regions and southward to the entire Gulf Coast from Texas to Florida. Below normal precipitation is favored for much of the Pacific Northwest, the Northern Rockies, and extending southeastward into the Central Rockies, parts of the northern Great Basin, and northeast regions of the Four Corners region. Equal chances (EC) of below, near and above normal precipitation are indicated for northern Alaska, as well as remaining areas of the Southwest CONUS, the western Great Plains, the Upper Mississippi Valley, the Great Lakes region, and the Northeast. During the late summer and early fall season, increased chances of above normal temperatures expand to include the entirety of the CONUS with the largest probabilities over the Southwest and Northeast. Chances of above normal precipitation remain elevated across much of the Midwest, Southeast, and mid-Atlantic into August-September-October, while elevated chances of below normal precipitation shift southeastward from the Pacific Northwest into northern areas of the Southwest region. In autumn 2020 elevated chances of above normal precipitation are introduced into the Pacific Northwest and expand into the northern to central Great Plains in winter 2020-2021, then shift eastward into the Midwest by spring 2021. Increased chances of below normal precipitation expand across the southern tier of the CONUS in September-October-November 2020 through November-December-January 2020-2021. Equal chances (EC) are forecast in areas where the likelihood of seasonal mean temperatures or seasonal accumulated precipitation amounts are expected to be similar to climatological probabilities. BASIS AND SUMMARY OF THE CURRENT LONG-LEAD OUTLOOKS Note: For Graphical Displays of the Forecast Tools Discussed Below See: http://www.cpc.ncep.noaa.gov/products/predictions/90day/tools/briefing CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS Oceanic and atmospheric observations across the equatorial Pacific indicate ENSO-neutral conditions persisted into June. Observed SSTs, for the previous 30 days, showed average or positive anomalies west of the Date Line and negative anomalies from 160 degrees W longitude eastward to near the coast of South America. Positive subsurface temperature anomalies continued to be confined to the western Pacific with increasing negative temperature anomalies below the surface of the eastern Pacific. Integrated upper-ocean heat anomalies declined rapidly since earlier this spring and remain significantly negative. Easterly low-level wind anomalies were present east of the Date Line during the previous 30 days with westerly upper-level wind anomalies along the equator over the central and east-central Pacific Ocean. Positive outgoing longwave radiation (OLR) anomalies, during this same time period, show suppressed convection across the western and central equatorial Pacific. PROGNOSTIC DISCUSSION OF SST FORECASTS The CPC SST Consolidation for the Nino 3.4 region indicates a steady decline into increasing negative anomalies to -0.5 degrees C by JAS with negative anomalies peaking during the early winter. The SST canonical correlation analysis (CCA), constructed analog (CA), and Markov statistical models indicate a persistence of ENSO-neutral conditions through the summer and fall into winter. The CPC/IRI consensus forecast favors a continuation of ENSO-neutral conditions (with about a 60 percent chance) during the Northern Hemisphere summer with the chances decreasing through the autumn (to 40-50 percent) and approximately an equal chance (40-50 percent) of developing La Nina conditions. PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS Tools used for the seasonal outlooks included dynamical model guidance such as the North American Multi-Model Ensemble (NMME) and the Calibration, Bridging, and Merging (CBaM) version of the NMME. Current soil moisture conditions played a role in the JAS temperature outlook, primarily across the Great Plains and Four Corners region. The seasonal consolidation tool, which includes dynamical model input from the NMME and various statistical tools such as regressions of observed temperature and precipitation on the CPC Nino 3.4 SST consolidation, was used especially at later leads. The likelihood that either ENSO-neutral or La Nina will be present later this summer through the autumn and winter seasons played a role in both temperature and precipitation outlooks. During the 2021 warm season decadal trends were the primary source of climate signals. PROGNOSTIC DISCUSSION OF OUTLOOKS - JAS 2020 TO JAS 2021 TEMPERATURE Above normal temperatures are likely across almost the entire CONUS and Alaska during JAS with the largest probabilities forecast across the West and Northeast, based on excellent agreement among dynamical and statistical forecast tools including a strong decadal signal. Probabilities of above normal temperatures were increased from eastern Nevada into the Four Corners region from the previous JAS outlook following the latest model guidance, consistent with an increasing signal for below normal precipitation for much of this region, and ongoing low soil moisture conditions. Conversely, high soil moisture is one of the factors for equal chances of below, near or above normal temperatures forecast for parts of the Central Mississippi Valley in JAS. Beginning in ASO, increased chances of above normal temperatures expand through the central U.S. as the effect of anomalous soil moisture wanes and decadal trends support a larger signal for above normal temperatures. From JAS through OND 2020, changes from the previous outlook were to slightly increase probabilities of above normal temperatures for the Southwest and to decrease probabilities of above normal temperatures for the Pacific Northwest to northern Rockies. These minor changes were based on the latest consensus among dynamical and statistical tools and influenced by the equal chances of La Nina ans ENSO neutral conditions and low probability of El Nino. An expected lack of sea ice due to decadal trends elevates the probabilities for above normal temperatures across northern Alaska during the autumn season. The temperature outlook for the longer lead times following the spring of 2021 are based largely on decadal timescale trends. PRECIPITATION The precipitation outlooks are based primarily on the latest dynamical model guidance through DJF, along with statistical models, including the signal due to decadal trends, through JAS 2021. Compared to the previous outlook for JAS, a slight northeastward shift was made in the area of enhanced chances of below normal precipitation over the Four Corners region, as some model guidance such as from the CBaM Bridging component related to ENSO impacts, indicate potential enhanced precipitation over southwestern areas of the Southwest monsoon region. Consistent with the NMME and consolidation tool, probabilities above 40 percent for above normal precipitation were expanded from the eastern Gulf Coast into the Central Mississippi and Ohio Valleys. Elevated probabilities of above normal precipitation were indicated for southern Alaska, as supported by dynamical model guidance. Elevated chances of above normal precipitation were introduced into the Pacific Northwest in autumn and early winter, compared to previous outlooks, following dynamical model guidance and potentially associated with the equal likelihood of ENSO neutral or La Nina. A signal for below normal precipitation continues throughout the southern tier of the CONUS through autumn into early winter. No changes were made to the precipitation outlook from JFM 2021 onward, as the future evolution of interannual variability and ENSO remain uncertain. At the longer leads, MJJ through JAS 2021, the tilt in the odds towards above normal precipitation across parts of the central and eastern U.S. is consistent with decadal trends. The area of favored below normal precipitation for parts of the Southwest during the spring 2021 is consistent with decadal trends. FORECASTER: Dan Collins The Climatic normals are based on conditions between 1981 and 2010, following the World Meterological Organization convention of using the most recent 3 complete decades as the climatic reference period. The probability anomalies for temperature and precipitation based on these new normals better represent shorter term climatic anomalies than the forecasts based on older normals. For a description of of the standard forecast tools - their skill- and the forecast format please see our web page at http://www.cpc.ncep.noaa.gov/products/predictions/long_range/tools.html (Use Lower Case Letters) Information on the formation of skill of the CAS forecasts may be found at: http://www.cpc.ncep.noaa.gov/products/Soilmst_Monitoring/US/Outlook/outlook.shtm l (use lowercase letters) Notes - These climate outlooks are intended for use prior to the start of their valid period. Within any given valid period observations and short and medium range forecasts should be consulted. This set of outlooks will be superseded by the issuance of the new set next month on Jul 16 2020 1981-2010 base period means were implemented effective with the May 19, 2011 forecast release. $$