Prognostic Discussion for Long-Lead Seasonal Outlooks NWS Climate Prediction Center College Park MD 830 AM EDT Thu Jun 20 2019 SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS The July-August-September (JAS) 2019 temperature outlook indicates that above normal seasonal mean temperatures are most likely for the western third of the CONUS and all of Alaska. The highest odds for above normal temperatures are across Washington and the Alaska Panhandle. Above normal temperatures are also favored for Southern Texas, the Gulf Coast states, and east of the Appalachian Mountains. Below normal temperatures are the most likely category from the Central and Southern Plains to the Upper Great Lakes. 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 during May 2019. Sea surface temperatures (SSTs) across much of the equatorial Pacific Ocean remain above climatological averages, with anomalies ranging from 0 to +1C from 160E to 130W. East of 130W, temperatures are closer to average with smaller scale features evident. The latest weekly Nino 3.4 SST anomaly is +0.7 degree C. Oceanic heat content, determined from ocean temperature anomalies from the surface to a depth of 300 meters along the near equatorial Pacific from the Date Line to 100W, has increased to about 0.5C since reaching a local minimum during May. Atmospheric conditions, are showing less of a canonical response when looking at monthly average wind anomalies. The drop in oceanic heat content and lack of coherent wind response is likely related to stronger subseasonal variability related to the Madden-Julian Oscillation (MJO) during May and early June. Collectively, these oceanic and atmospheric conditions represent a continuation of weak El Nino conditions as of May 2019. Other boundary conditions relevant to the seasonal outlook are soil moisture anomalies and, in some areas, near-coastal SSTs. Widespread and persistent above normal precipitation for most of the CONUS during recent months has resulted in positive soil moisture anomalies for many areas of the central and eastern CONUS, extending into parts of the Great Basin, with many of these areas exceeding the 99th percentile of climatological soil moisture. Sea ice coverage for the Arctic is at record low amounts and SSTs are above normal near the west coast of Alaska. PROGNOSTIC DISCUSSION OF SST FORECASTS The CPC SST Consolidation Nino 3.4 forecast indicates the continuation of an El Nino through 2019. The three statistical models all predict at least a weak El Nino from autumn 2019 into winter 2019-2020, with the CCA predicting a moderate strength El Nino by Dec-Jan-Feb 2019-2020. The CFS dynamical model forecast ensemble mean predicts a slow decline in positive Nino 3.4 anomalies, with the most recent runs indicating a transition to ENSO neutral conditions during the autumn of 2019. The NMME suite of dynamical models shows more spread (implying less certainty in the outlooks through the rest of 2019. Most of the models indicate either a weak El Nino or ENSO neutral. Little possibility of a La Nina event next winter is indicated by statistical and dynamical model forecasts. The probability of a continuation of the current El Nino through the 2019 summer is 66%, with a 50-55% chance of it continuing into the fall and winter. PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS The temperature and precipitation outlooks were based primarily on dynamical model guidance from the NMME, IMME, and statistical model guidance which includes a statistical forecast of the linear impacts of ENSO combined with decadal climate trends based on the CPC SST Consolidation forecast for Nino 3.4. The potential impacts from a continuation of El Nino conditions were considered for the seasonal outlook period through winter 2019-2020. Soil moisture conditions were strongly considered for the earliest leads, as well as near-coastal SST anomalies. Several statistical and dynamical models, as well as hybrid statistical-dynamical models, along with an objective 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. The potential for an out sized influence from subseasonal variability to imprint on the seasonal period was also considered for the early leads, as given a weak El Nino, subseasonal modes of variability can have a larger than normal influence. PROGNOSTIC DISCUSSION OF OUTLOOKS - JAS 2019 TO JAS 2020 TEMPERATURE The JAS 2019 through DJF 2019-2020 seasonal mean temperature outlooks utilize the predictability of several climate phenomena, including the ongoing El Nino event and its potential impacts, anomalous land surface and sea surface temperature states, and decadal timescale climate variability or trends. 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) suggest that below-normal temperatures are most likely during JAS over much of the central CONUS. Many of the dynamical models in the NMME suite indicate below normal temperatures. Statistical guidance that emphasizes ENSO and long-term trends indicate that near normal temperatures are most likely for much of the same area, while a pure ENSO response would favor below normal temperatures potentially across the Great Lakes through Aug-Sep-Oct (ASO). Two inputs, summertime ENSO and the relation of temperature to soil moisture, offer less predictability in the autumn, so the SON and OND outlooks largely reflect the model guidance and linear regressions of trend and ENSO. The outlooks beyond OND are largely unchanged from the prior months set as the odds for El Nino to continue are nearly the same as last month. On the seasonal timescale, during the summer and autumn, trends are the dominant mode of variability across Alaska, and trends favor above normal temperatures. The strongest signal is during the months of October and November, and the current outlook reflects strong probabilities for above normal temperatures during the seasons that include those months. PRECIPITATION Beginning with the JAS 2019 precipitation outlook, above normal precipitation is forecast for a large region of the CONUS from the interior West to the Mississippi Valley. This pattern is suggestive of a northward shift in the North American Monsoon, and is supported by model guidance and statistical relationships between seasonal precipitation and ENSO. For JAS 2019, some models showed weak signals for below normal precipitation from the Northeast to the Mid-Atlantic, though only the Mid-Atlantic portion of that signal is consistent with ENSO composites/regressions, so the overall signal was not included in the official outlooks. The pattern in the precipitation forecast persists for the ASO 2019 season, though during ASO the signal shifts south to reflect the potential for moisture to surge northward from the East Pacific, an impact typically associated with more tropical cyclone activity. Beyond ASO, the signal gradually shifts southward due to the seasonal evolution of long-term trends and expected ENSO impacts during the winter of 2019-2020. Similar to the temperature outlooks, minimal changes were made to the outlooks covering winter 2019-2020 and spring 2020 as no forecasts of major climate factors have changed since last month. The outlooks for next summer were modified to reflect trends, including the addition of below normal precipitation across the interior Pacific Northwest. FORECASTER: Matthew Rosencrans 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 18 2019 1981-2010 base period means were implemented effective with the May 19, 2011 forecast release. $$