Prognostic Discussion for Long-Lead Seasonal Outlooks NWS Climate Prediction Center College Park MD 830 AM EDT Thu Apr 18 2019 SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS The May-June-July (MJJ) 2019 temperature outlook indicates that above normal seasonal mean temperatures are most likely for the eastern and western thirds of the US, including Alaska. The greatest probabilities exceed 50% for the southern coast of Alaska, including the Alaska Panhandle, the Pacific Northwest, and for the Northeast region extending southward along the east coast to Florida. Below normal seasonal mean temperatures are more likely for parts of the Central and Southern Plains. The MJJ 2019 precipitation outlook indicates that above normal seasonal total precipitation is most likely for much of the US, including the interior West across much of the Great Plains into the Central Mississippi and Ohio Valleys, the Southeast region, and along the Atlantic Coast from Florida to the Mid-Atlantic. The greatest probabilities for above normal seasonal total precipitation are for areas of the Central Rockies. Below normal precipitation is more likely for a small area of the Pacific Northwest near the coast. Above normal precipitation is more likely for most of Alaska, with below normal more likely for the Alaska Panhandle. Equal Chances (EC; white areas) of below, near, and above normal seasonal mean temperatures or seasonal total precipitation amounts are where the likelihoods for these three categories are similar to their climatological probabilities. Review of subsequent seasonal outlooks and the scientific forecast basis for all outlooks are given below. 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 El Nino conditions continued in the Pacific Ocean through April 2019. Sea surface temperatures (SSTs) across much of the equatorial Pacific Ocean remain above climatological averages with areas above +1.0 degrees C from the central to the eastern Pacific for the most recent 4-week average. The latest weekly Nino 3.4 SST anomaly is slightly below +1 degree C. Oceanic heat content, determined from ocean temperature anomalies from the surface to a depth of 300 meters along the equatorial Pacific, has decreased in the last month after increasing over the prior two months. Atmospheric conditions continue to respond to the anomalous SST forcing with enhanced convection consistently along the equator near the Date Line during the last few months. Modest low-level westerly wind anomalies were observed along the equator over the western Pacific, and an upper-level anticyclonic circulation was observed north of the equator in the central Pacific along with easterly upper-level anomalies from the central to the western Pacific. Collectively, these oceanic and atmospheric conditions represent a continuation of weak El Nino conditions as of April 2019. Other boundary conditions relevant to the seasonal outlook are soil moisture anomalies, current snow depth anomalies, and in some areas near-coastal SSTs. Widespread and persistent above normal precipitation for most of the CONUS during recent months and especially during February and March has resulted in positive soil moisture anomalies for parts of the Southwest and for many areas of the central and eastern CONUS. Sea ice coverage along much of the western Alaska coast is below normal, with SSTs above normal. PROGNOSTIC DISCUSSION OF SST FORECASTS The CPC SST Consolidation Nino 3.4 forecast indicates the continuation of an El Nino through 2019. There is considerable spread, however, among its constituent input models with the constructed analog (CA) indicating persistent ENSO neutral conditions, while the CCA and Markov statistical models predict an increase in positive Nino 3.4 anomalies from late summer 2019 through the winter of 2019-2020. The CFS dynamical model forecast ensemble mean predicts a slow decline in positive Nino 3.4 anomalies after an initial increase in the spring. The NMME suite of dynamical models also shows large spread with some ensemble members predicting a strong El Nino event by the beginning of winter, some maintaining a weak or moderate event through autumn, and some members predicting a return to ENSO neutral conditions by autumn. Little possibility of a La Nina event next winter is indicated by statistical and dynamical model forecasts. While La Nina events often emerge in the year following an El Nino in the climate record, at other times El Nino events extend beyond one year, as predicted by a significant number of the forecast tools. The probability of a continuation of the current El Nino into next winter is set at about 50% by the IRI/CPC consensus forecast. PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS The temperature and precipitation outlooks were based primarily on dynamical model guidance from the NCEP CFS, as well as the NMME, along with statistical model guidance, including a statistical forecast of the impacts of ENSO combined with decadal climate trends based on the CPC SST Consolidation forecast for Nino 3.4. The potential impact from a possible continuation of El Nino conditions were considered for the seasonal outlook period through next winter 2019-2020. Soil moisture conditions were considered, as well as recent snowpack observations, and near-coastal SST anomalies. Several statistical and dynamical models, as well as hybrid statistical-dynamical models, along with a consolidation of several forecast tools, were also examined in preparation of the seasonal outlooks. Decadal timescale trends were considered for all leads but take a primary role in later outlooks, as uncertainty in interannual climate signals increases. PROGNOSTIC DISCUSSION OF OUTLOOKS - MJJ 2019 TO MJJ 2020 TEMPERATURE The MJJ 2019 through JFM 2020 seasonal mean temperature outlooks utilize the predictability of several climate phenomena, including the potential of an ongoing El Nino event and its potential impacts, anomalous land surface and sea surface temperature states, and decadal timescale climate variability or trends. Probability anomaly calibrated (PAC) forecasts derived from the NMME, a statistical-dynamical hybrid model combining calibrated NMME temperature forecasts with statistically bridged impacts from NMME Nino 3.4 forecasts (known as calibration, bridging and merging or CBaM), as well as a consolidation of statistical and dynamical tools predict that below normal temperatures are most likely for an area of the Central and Southern Plains during MJJ 2019. These models predict that above normal temperatures are likely for Alaska, as well as much of the western and eastern CONUS beginning in MJJ 2019 and continuing through all outlooks, where interannual climate signals and other shorter timescale climate forcings are either in phase with decadal warming trends or positive temperature trends are greater than shorter timescale climate signals. Greater probabilities exceeding 50% of above normal temperatures expand across the West through summer 2019, while probabilities of above normal temperatures decrease below 40% across southern tier states beginning in the Southwest region and continuing across the southern CONUS into the Southeast by early winter, due to the potential impact if El Nino persists through these seasons. Areas with enhanced probabilities of above normal temperatures expand into the Southern Plains in JJA and JAS 2019, as the signal due to positive soil moisture anomalies decreases. Areas with likely above normal temperatures further expand into the Central and Northern Plains in ASO and SON 2019, driven in part by decadal climate trends and supported by dynamical and statistical models and the consolidation forecast. Temperature outlooks for OND 2019 and later are largely based on the consolidation, deriving signals from statistical model forecasts, based largely on decadal trends and the possible states of ENSO. Above normal temperatures are most likely for all regions in the NDJ and DJF winter 2019-2020 outlooks, with an area of uncertainty and decreased probabilities of above normal appearing in the north-central CONUS in the JFM through MJJ 2020 outlooks. PRECIPITATION Beginning with the MJJ 2019 precipitation outlook, above normal precipitation is forecast for a large region of the CONUS from the interior West across the much of the Great Plains to the Gulf and Atlantic coasts. This general precipitation forecast pattern persists with some reduction in probabilities for the JJA 2019 season. For MJJ 2019, below normal precipitation is most likely for parts of the Alaska Panhandle and the Pacific Northwest. The region of enhanced probabilities for above normal precipitation over the CONUS steadily decreases in area from JAS through SON 2019, with decreasing signals for the Gulf and Atlantic coasts in JAS and ASO 2019. The area of enhanced probabilities of above normal precipitation expands into the Southwest from JAS through SON 2019, due to forecasts of continued above normal SSTs over the eastern Pacific Ocean, related to the potential persistence of El Nino, along with potential moisture surges into the Southwest monsoon region related to enhanced tropical storm activity. Probabilities of above normal precipitation are enhanced for much of Alaska outside the Alaska Panhandle in MJJ and JJA 2019, and for various regions of Alaska from JAS through all seasonal outlooks, driven by signals related to decadal climate trends and interannual climate signals, such as a persistence of El Nino. Decadal precipitation trends lead to enhanced probabilities of above normal precipitation for parts of the Northeast CONUS in AMJ and MJJ 2020. Precipitation outlooks are based primarily on dynamical model guidance from the NMME and CBaM through SON 2019, and the consolidation of statistical forecast tools and trends from OND 2019 through MJJ 2020. 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 May 16 2019 1981-2010 base period means were implemented effective with the May 19, 2011 forecast release. $$