Prognostic Discussion for Long-Lead Seasonal Outlooks NWS Climate Prediction Center College Park MD 830 AM EST Thu Nov 21 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 December-January-February (DJF) season. Additional information related to the forecast for this season and subsequent 3-month overlapping seasonal outlooks through DJF 2020-2021 are also given below. The DJF 2019-2020 temperature outlook favors above-normal seasonal mean temperatures for Alaska and most of the western and southern contiguous U.S., with modest probabilities in favor of above-normal temperatures extending up the Eastern Seaboard. Equal-chances (EC) is indicated over a large swath of the north-central U.S. where climatological odds for either of the three categories (below-, near- or above-normal) are forecast. The DJF 2019-2020 precipitation outlook favors above-normal seasonal total precipitation amounts for Alaska (especially the Southwest portion of the state) and much of the northern tier of the contiguous U.S. Smaller areas of favored below-normal seasonal precipitation amounts are highlighted for parts of California and the Southwest, as well as the western Gulf Coast and lower Mississippi Valley. Remaining areas of the forecast domain denote Equal-Chances (EC) where climatological odds for either of the three categories (below-, near- or above-normal) are 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 weekly Nino3.4 index value has spiked to +0.8 degrees C, but this is largely due to tropical subseasonal activity associated with the MJO. Broadly positive SST anomalies are now observed over nearly the entire equatorial Pacific. A review of the ocean sub-surface reveals shoaling of a downwelling Kelvin wave in the eastern Pacific, as expected from last month's outlook. The overlying atmospheric circulation is unremarkable, consistent with ENSO neutral conditions. The SOI has been consistently negative over the past three months, but the equatorial SOI has hovered near zero. 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. Extratropical SSTs of this magnitude, however, may play a small role in the coming seasons. 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 over the eastern Indian Ocean and Maritime Continent. It is unclear how this forcing affects the forecast circulation over North America, though the various coupled model systems do indicate some wave train propagating away from this source region. 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. The various dynamical and statistical tools weaken the strong IOD signal over the coming months, and maintain the strongly positive SST anomalies over the Northeast Pacific. 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. Experimental, empirical forecasts of the North Atlantic Oscillation (NAO) and North Pacific Oscillation-West Pacific pattern (NPO-WP) are utilized to support the consensus of the statistical tools especially during later winter and early Spring. These forecasts utilize SST, sea ice coverage, and stratospheric circulation as predictors in a multiple regression model. This model predicts negative phases of both the NAO and NPO-WP for the upcoming winter, with stratospheric predictors driving the NAO forecast and Pacific SST patterns driving the NPO-WP forecast. PROGNOSTIC DISCUSSION OF OUTLOOKS - DJF 2019 TO DJF 2020 TEMPERATURE The DJF 2019-2020 temperature outlook is informed by the objective consolidation, but heavily adjusted to account for the latest CFSv2 runs, the international model suite, and the empirical NAO and NPO-WP guidance. This has the effect of reducing above-normal temperature probabilities over the north-central CONUS, Midwest, and Great Lakes to equal-chances (EC). In JFM through MAM seasons, the statistical guidance is more heavily utilized to depict enhanced probabilities of below-normal temperatures across parts of the northern tier of the CONUS. This is especially apparent in the SST constructed analog, but also consistent with the CCA and ENSO-OCN tools. The latest CFSv2 runs (initialized over the past 10 days) depicts a colder solution relative to long-term trends centered over eastern Canada and the northernmost parts of the Northeast CONUS for the DJF through FMA seasons, more consistent with the international model blend and less so with the NMME. In many ways the forecast temperature evolution is similar to the long-term trends as assessed by the optimal climate normals. This seems appropriate given the conflicting signals between the dynamical models and the statistical models on many key features, including the seasonal phase of the NAO. The remaining forecasts throughout 2020 across the CONUS and Alaska are largely derived from an objective, skill-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. Long-term temperature trends become less dominant heading into late fall and winter 2020-2021. PRECIPITATION The DJF 2019-2020 precipitation outlook depicts above-normal seasonal total precipitation amounts for all of Alaska and most of the northern tier of the CONUS. Modestly elevated odds for below-normal precipitation are depicted for small regions of the southern West Coast and western Gulf Coast. 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. Statistical-dynamical guidance consolidation and long-term precipitation trends are the primary basis for the forecast over the entire forecast period. These are consistent with the consensus of dynamical model guidance through spring 2020, which may be related to forecast SST gradients in the tropical Pacific being associated with suppressed convection near and east of the Date Line. The majority of forecast tools support expansion of favored below-normal precipitation from Texas to the Southwest by JFM 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. These trends appear consistently across the statistical forecast suite and, during the warm season, favor a tilt toward dry (wet) across parts of the western (eastern) CONUS. FORECASTER: Stephen Baxter 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 Dec 19 2019 1981-2010 base period means were implemented effective with the May 19, 2011 forecast release. $$