Prognostic Discussion for Long-Lead Seasonal Outlooks NWS Climate Prediction Center College Park MD 830 AM EDT Thu Jun 17 2021 SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS ENSO-neutral conditions are present across the equatorial Pacific Ocean, as represented in current oceanic and atmospheric observations. The official CPC ENSO forecast indicates that ENSO-neutral conditions are likely to persist through the fall. Looking further ahead, El Nino is the least likely scenario through the upcoming winter. The July-August-September (JAS) 2021 temperature outlook favors above normal temperatures for Alaska, the western half of the CONUS, the eastern quarter of the CONUS, and the Northern Plains, with the largest probabilities (greater than 60 percent) forecast across the Northeast. The JAS 2021 precipitation outlook depicts enhanced probabilities of below normal precipitation amounts across the Pacific Northwest, Rockies, and parts of the High Plains. Above-normal precipitation is more likely from the Eastern Seaboard to the Lower Mississippi Valley and parts of the Southern Plains. Above normal precipitation amounts are slightly favored for parts of northwestern Alaska. Equal chances (EC) are forecast for areas where probabilities for each category of seasonal mean temperatures and 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 The coupled oceanic and atmospheric observations reflect ENSO-neutral conditions. During the past four weeks, sea surface temperatures (SSTs) returned to near average across most of the equatorial Pacific Ocean. In the last two months, positive subsurface temperature anomalies extended across most of the Pacific Ocean. However, recently, negative anomalies have emerged in the Central Pacific at 50-200m depth. Beginning in mid-March, integrated upper-ocean heat anomalies have been positive. Since early May, these positive anomalies have weakened to near zero. During the past 30 days, suppressed convection was located south of the Equator near the Date Line and over parts of Indonesia. Enhanced convection was evident over the far western Pacific Ocean. The RMM index recently emerged over Africa with enhanced convection noted over the tropical Atlantic. A weakening of this signal is anticipated and models are predicting a potential new intraseasonal feature over the Western Hemisphere by late June. PROGNOSTIC DISCUSSION OF SST FORECASTS A majority of the models in the IRI/CPC plume predict ENSO-neutral to continue through the fall 2021. By the late fall and winter, La Nina chances increase to near 50 percent, reflecting the historical tendency for a second winter of La Nina following the first, and also the predictions from the North American Multi-Model Ensemble. However, these cooler conditions are predicted to exist for a short duration (3 overlapping seasons) and these predictions are still over 6 months into the future. In summary, ENSO-neutral is favored through the Northern Hemisphere summer (greater than 60 percent chance for the JAS season) and fall (50 percent chance for the SON season). El Nino is the least likely scenario (less than 10 percent chance) through the upcoming winter. PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS Dynamical model forecasts from the NMME and Copernicus (C3S) multi-model ensemble systems are used extensively for the first six leads when they are available, as was the objective, historical skill weighted consolidation, that combines both dynamical and statistical forecast tools. Additionally, the official ENSO forecast depicts probabilities of El Nino that are significantly less than climatological probabilities through the upcoming winter. This anticipated lack of an El Nino signal played a role in the construction of these outlooks. Anomalously wet (dry) soil moisture conditions was also a factor in the temperature outlook across the Southern Plains and Lower Mississippi Valley (northern Great Plains) during summer and early fall. At later leads, decadal trends in temperature and precipitation were increasingly relied upon in creating the seasonal outlooks. PROGNOSTIC DISCUSSION OF OUTLOOKS - JAS 2021 TO JAS 2022 TEMPERATURE Above normal temperatures are favored throughout a majority of the forecast domain during JAS, except for parts of the Southern and Central Plains and the Lower and Middle Mississippi Valley, where equal chances (EC) of below, near, or above normal temperatures are forecast. This EC area is due to weaker signals among temperature tools coupled with abnormally wet soil moisture conditions across most of this region and represents a reduction in above normal temperature probabilities relative to last month's outlook. Probabilities of above normal temperatures are increased relative to last month across the Northern Plains due, in part, to continued dry soils. Chances of above normal temperatures are also increased for the Northeast due to excellent agreement among both dynamical and statistical guidance. Above normal temperatures are favored throughout Alaska during JAS, but with a reduction of probabilities across the Panhandle compared to last month where dynamical model support is the weakest. From ASO through SON, above normal temperatures are favored across the entire CONUS as soil moisture impacts begin to diminish. Thereafter, the forecast pattern increasingly begins to reflect trends with above normal temperatures favored across the southern and eastern CONUS through the fall, winter, and next spring. Probabilities of above normal temperatures peak in the Southeast during the winter, consistent with an anticipated absence of El Nino, and again later next Spring, as trends play a greater role. Conversely, below normal temperatures are slightly favored for the Northern Plains late this upcoming winter into early spring consistent with recent trends and corresponding to a strong cold signal from ENSO composites. Elevated chances of above normal temperatures return to the entire West Coast by late next Spring consistent with trends. Forecast uncertainty is generally high across much of Alaska, where warm trends conflict with colder ENSO composites and dynamical model guidance to varying degrees. EC is forecast across much of southern Alaska from late fall through early spring where disagreements among these conflicting tools are at its greatest. Otherwise above normal temperatures are generally forecast for northern Alaska where the trend signal is the strongest. PRECIPITATION Model guidance remains consistent from previous months depicting elevated probabilities of below normal precipitation for the Pacific Northwest, Rockies, and northern to central High Plains during JAS. However, the strength of the signal diminishes considerably farther to the south, resulting in a forecast of EC across much of the Southwest Monsoon Region. Farther to the east, above normal precipitation is favored from the Southern Plains to the Northeast. The highest confidence for above normal precipitation is across the Lower Mississippi Valley, consistent with the strongest signal among dynamical model guidance, and for parts of the Mid-Atlantic States and the Northeast, where statistical tools depict the strongest signal. A small region of elevated probabilities of above normal precipitation is also indicated for parts of northwestern Alaska, consistent with CPC's skill weighted consolidation tool. EC is indicated for the rest of the forecast domain as signals for the various dynamical and statistical tools are too weak or conflicting to issue a forecast with a sufficient degree of confidence. As we progress further into late summer and into the fall, dynamical and statistical guidance converge on a drier solution for the Southwest Monsoon Region. This dry signal is consistent with the anticipated absence of El Nino conditions and, consequently, the potential inhibition of tropical activity in the Pacific. Looking further ahead the dry signal expands eastward to encompass the entire Southern Tier from coast to coast by late fall through most of the winter, consistent with absence of El Nino. Thereafter, a region of elevated probabilities of above normal precipitation is indicated for parts of the Mississippi and Ohio valleys late winter into early spring consistent with trends. This region of favored above normal precipitation expands southward to the Southern Plains and eastward to parts of the East Coast during the spring consistent with trends and ENSO composites. Trends also favor dryness for parts of the western CONUS as we progress deeper in the Spring into next summer. As was the case with temperature, uncertainty in the precipitation forecast across much of Alaska is quite high and EC is indicated across much of the state for all forecast leads. However above normal precipitation is favored for parts of the South Coast late in the summer into early fall consistent with ENSO composites and the C3S. Above normal precipitation is also favored for northern Alaska beginning in the fall through early spring due to trends and for eastern Alaska during the winter due to a wet ENSO signal. Trends and ENSO composites also lead to favored wetter than normal conditions for parts of eastern Alaska next summer. FORECASTER: Scott Handel The Climatic normals are based on conditions between 1991 and 2020, 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 15 2021 1991-2020 base period means were implemented effective with the May 19, 2011 forecast release. $$