Prognostic Discussion for Long-Lead Seasonal Outlooks NWS Climate Prediction Center College Park MD 830 AM EDT Thu Oct 17 2019 SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS Oceanic and atmospheric conditions in the equatorial Pacific Ocean reflect an ENSO-neutral state and these conditions are forecast to continue through the winter and spring of 2019-2020. Additional details regarding tropical conditions are provided below. Here we focus on a summary of the first 3-month seasonal outlook for temperature and precipitation for the November-December-January (NDJ) season. Additional information related to the forecast for this season and subsequent 3-month overlapping seasonal outlooks through NDJ 2020-2021 are also given below. The NDJ 2019-2020 temperature outlook favors above-normal seasonal mean temperatures for Alaska and most of the contiguous U.S., with the greatest probabilities forecast for northwest Alaska and the Southwest U.S. where probabilities exceed 60% and 50% respectively. Odds for above-normal temperatures are more modest for most of the eastern U.S. and a small region in the upper-Mississippi valley is denoted Equal-Chances (EC) where climatological odds for either of the three categories (below-, near- or above-normal) is forecast. The NDJ 2019-2020 precipitation outlook favors above-normal seasonal total precipitation amounts for Alaska (especially the Southwest portion of the state) and for a region from New Mexico northward to include the northern Rockies, northern and central Great Plains and the north-central Mississippi Valley. Smaller areas of favored below-normal seasonal precipitation amounts are highlighted for the central West coast and central Gulf Coast. Remaining areas of the forecast domain denote Equal-Chances (EC) where climatological odds for either of the three categories (below-, near- or above-normal) is forecast. 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 As noted in the summary, oceanic and atmospheric indicators show current ENSO-neutral conditions. The most recent Nino3.4 index is +0.4 degrees C, but there is variation in sea surface temperature (SST) anomalies along the equatorial Pacific from west of the Date Line to the South American coast. Greater than +1.0 degree C anomalies remain east of Papua-New Guinea while small negative SST anomalies are depicted in the eastern Pacific ocean. A review of the ocean sub-surface does depict cooler SSTs in the eastern portion of the Pacific basin are likely connected to the shoaling of an upwelling oceanic Kelvin wave in recent weeks. The subsurface ocean data also shows, however, a downwelling oceanic Kelvin wave shifting eastward at depth in the central Pacific. This wave is likely to reach the south American coast in coming weeks and moderate SSTs to some degree in the central and eastern Pacific in November to most likely weakly positive anomalies. Two other areas of ocean anomalies need to be watched in the coming couple of months. One is a large area of positive SST anomalies ranging from 1-3 degrees C north of 20 N in the northeast Pacific Ocean. Extratropical SST anomalies, although often impressive in scale, can change rapidly due to mid-latitude wave activity and the associated variation in mean storm tracks. But this regional SST anomaly can be utilized, to some degree, as a predictor for the first lead of the current seasonal outlook package. Also, a strong Indian Ocean Dipole (IOD) is currently in place with above-normal SSTs in the western Indian Ocean and below normal SSTs in the eastern Indian Ocean and waters in proximity to the Maritime continent. The atmosphere has responded to this boundary forcing with stationary enhanced convection observed for several weeks across Africa and the western Indian Ocean with stationary suppressed convection observed from the eastern Indian Ocean eastward across the Maritime continent into the west Pacific to near the Date Line. This is important because if suppressed convection persists in the western Pacific along with the absence of any organized, large scale enhanced convection further east in the Pacific, it may tend to favor more frequent periods of a retracted east Asian-Pacific jet and so in some ways mimic La Nina like conditions downstream - mainly during the few early leads in the forecast package. Positive soil moisture anomalies remain quite high and in fact much of this area is observing values at or greater than the 99th percentile of the respective historical range. Flash drought conditions in the Southeast CONUS are favored to ease in coming weeks with favored above-normal rainfall during the second half of October. Moreover, as has been the case, SST anomalies range from +2.5 to +3.5 degrees C, or higher for waters surrounding Alaska. PROGNOSTIC DISCUSSION OF SST FORECASTS The CPC SST consolidation forecast, the NMME ensemble mean forecast and the official CPC / IRI probabilistic ENSO outlook for Nino3.4 all favor continued ENSO-neutral conditions through the upcoming winter 2019-2020 and spring 2020. There is, of course, considerable spread across the various model forecasts (statistical and dynamical) over the next 6 months. A few dynamical models favor a tendency toward bordering on weak La Nina (as characterized by Nino3.4) by late winter while the majority remain in ENSO-neutral territory or tend toward borderline weak El Nino over the same period. The expectation of ENSO-neutral conditions was utilized in making this month's seasonal outlook package. PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS The temperature and precipitation outlooks were based on currently depicted, organized, large scale SST anomaly patterns (i.e., ENSO-neutral, IOD, northeast Pacific SSTs, and near Alaska SSTs), both temperature and precipitation long term climate trends, bias-corrected and calibrated dynamical model forecasts from several sources, statistical forecast tools including the Constructed Analogue (CA) tool using near global SSTs as the primary predictor and an objective, historically skill weighted consolidation of (1) statistical tools only and (2) both statistical and dynamical forecast tools. Since ENSO is unlikely to provide a major influence on the mid-latitude circulation pattern, long term climate trends were weighted more heavily than normal during early and middle forecast leads. PROGNOSTIC DISCUSSION OF OUTLOOKS - NDJ 2019 TO NDJ 2020 TEMPERATURE The NDJ 2019-2020 temperature outlook depicts high coverage of above-normal temperatures across the forecast domain. This forecast was supported by most statistical and dynamical model forecast guidance and long term positive temperature trends. The warm northeast Pacific ocean also somewhat favors warmer air entering the western CONUS for this season especially early on in the 3-month period. The high uncertainty of any persistence of this regional feature substantially limits its predictive value thereafter. The greatest odds for above-normal seasonal mean temperatures are for western Alaska and the Southwest CONUS at a greater than 60% and 50% probability respectively. For western Alaska, strongly above-normal SSTs in part associated with declining long term trends in sea ice coverage, multi-year ice (thickness) and later freeze dates contribute to these higher forecast odds. More modest odds for above-normal temperatures are forecast for the remaining areas of the forecast domain where climate signals and forecast tool consistency were somewhat less. A small region of Equal-Chances (EC) is denoted in the upper Mississippi Valley where some forecast tool information indicates somewhat less historical forecast skill and considerations are made for potentially increasing odds of below-normal temperatures at the end of this season. In this region the forecast is for no change from climatological odds (33%) for either above-, near- or below-normal seasonal mean temperatures. Progressing through the winter and spring seasons (DJF 2019-2020 - MAM 2020), the evolution of the forecast is for continued favored above-normal temperatures (albeit at lower odds) for the western and southern CONUS as forecast tools, both statistical and dynamical guidance, support this forecast. Moreover, combining objectively the associated impact from the CPC consolidation Nino3.4 SST forecast and long term positive temperature trends for these seasons supports this evolution of above-normal temperatures as well as the increase in spatial coverage of forecast uncertainty as depicted by EC areas through MAM 2020. Although odds are modest, elevated probabilities for below-normal temperatures are introduced in JFM 2020 in the northern Great Plains, increased in coverage in FMA 2020 (extended eastward to include the northern Great Lakes) and then decreased in areal extent in MAM 2020. Statistical guidance including negative long term temperature trends in some areas, especially in FMA 2020, along with enhanced odds of above-normal precipitation are the basis for the forecast. It is felt that the high probabilities of above-normal temperatures from most dynamical model guidance in this region may be overdone. Above-normal temperatures remained highly favored for Alaska peaking for the northwest coastal areas during MAM 2020 and again in SON 2020. The remaining forecasts throughout 2020 across the CONUS are largely derived from an objective, historically skilled weighted combination of statistical forecast tools and support large coverage of favored above-normal temperatures for most, if not all, of the forecast domain over the period. PRECIPITATION The NDJ 2019-2020 precipitation outlook depicts above-normal seasonal total precipitation amounts for all of Alaska and for a region stretching from New Mexico northward to include the northern Rockies and the north-central Great Plains and Upper Mississippi Valley. For Alaska, dynamical model guidance, long term positive precipitation trends and overall warmer, more open waters (potentially wetter, stronger cyclones) around the state support the forecast. Across the CONUS, strong climate signals for precipitation departures from climatology were few. For NDJ and DJF 2019-2020, statistical guidance consolidation and long term positive precipitation trends are the primary basis for the forecast in these two seasons. Modestly elevated odds for below-normal precipitation for small regions of the central West coast and central Gulf Coast are primarily based on dynamical model guidance and to a lesser extent long term negative precipitation trends. Progressing from DJF 2019-2020 through AMJ 2020, forecast areas of favored above-normal precipitation along the northern tier of the CONUS slowly shift from the northern Rockies and Great Plains to parts of the Great Lakes, Ohio Valley and mid-Atlantic. In addition to statistical guidance consolidation and long term positive precipitation trends, support for these highlighted areas also includes dynamical model guidance from the NMME from JFM through MAM 2020. At the same time, the majority of forecast tools support migration of favored below-normal precipitation from Texas to the Southwest and central and southern California by MAM 2020. The remaining outlooks are based on long term precipitation trends in the absence of more clear, reliable climate signals such as a confident ENSO prediction. FORECASTER: Jon Gottschalck 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 Nov 21 2019 1981-2010 base period means were implemented effective with the May 19, 2011 forecast release. $$