Prognostic Discussion for Long-Lead Seasonal Outlooks NWS Climate Prediction Center College Park MD 830 AM EST Thu Feb 20 2025 SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS La Niña conditions are present over the central and east-central equatorial Pacific, accompanied by below-average sea surface temperatures (SSTs) in this area. The latest weekly SST departure in the Niño 3.4 region is -0.3 degrees Celsius. La Niña conditions are expected to persist through February-April (FMA) 2025 with a 59% chance, with a 66% chance of a transition to ENSO-neutral during March-May (MAM) 2025. This La Niña is predicted to be weak and relatively short-lived, with the majority of guidance favoring SSTs in the Niño 3.4 region around -0.5 degrees Celsius. Though we still expect the canonical La Niña impacts through the MAM season, and possibly into the April-June (AMJ) season, there may be more variability within the season given the forecasted weakness of the event. The MAM 2025 Temperature Outlook remains very similar to last month, and favors below normal temperatures stretching from the northwestern Contiguous United States (CONUS) to the Northern Plains, as well as southeastern and southcentral Alaska. Above normal temperatures are forecast over the southern tier of the CONUS and much of the Eastern CONUS. Above normal temperatures are also forecast over northern and western Alaska. The highest probabilities of above normal temperatures reach 50 to 60% over parts of the Southwest, southern Texas, the southern Gulf States including Florida, and southern Georgia. The MAM Precipitation Outlook is similar in pattern to last month, which was and is a pattern that is canonical of La Niña in MAM. Above normal precipitation is favored over the Northwest, the Great Lakes and interior Northeast, Ohio and Tennessee Valleys, parts of the Mississippi Valley, and western and northern Alaska. Below normal precipitation is indicated over the Southwest, much of the Great Plains, the Gulf Coast, and the southern coast of Mainland Alaska. Equal Chances (EC) of above, near, and below normal temperatures or precipitation are indicated where there is model and/or tool disagreement, forecast probabilities for each category are similar, and temperatures or precipitation are expected to be close to the climatological distribution. 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 A weak La Niña continues over the central and east-central Pacific Ocean, with below-average SSTs observed across this region, and the latest weekly Niño 3.4 index at -0.3 degrees Celsius. The latest weekly Niño indices included +0.9 degrees Celsius in the Niño 1+2 region, +0.1 in Niño 3, and -0.7 degrees Celsius in Niño 4. The below-average SSTs have persisted in the central and east-central equatorial Pacific Ocean for at least the last two months. Negative subsurface temperature anomalies reached a minimum in late December, but have persisted overall since, and expanded to the central Pacific Ocean. Over the past 30 days, low-level wind anomalies were easterly from the western to central equatorial Pacific Ocean, and upper-level wind anomalies were westerly across the central and east-central equatorial Pacific Ocean on the southern flank of a large cyclonic circulation over the Pacific. Finally, tropical convection has been suppressed near the Date Line with enhanced convection over Indonesia. These atmospheric and oceanic indicators collectively reflect La Niña. The Madden-Julian Oscillation (MJO) made a near-circumnavigation of the global tropics during the past 40 days, with the most recent observations of the Realtime Multivariate MJO (RMM) index showing the enhanced phase near the interface between RMM phases 7 and 8 (near the interface between the Eastern and Western Hemispheres), with relatively modest amplitude outside the unit circle. For the next week or so, dynamical model RMM forecasts favored a slowed and erratic evolution of the MJO signal. Beyond this time however, forecasts depict a more canonical eastward propagation of the MJO that reaches the Indian Ocean towards the beginning of March. Forecasts of the MJO index are generally considered to be more relevant to the monthly outlook. PROGNOSTIC DISCUSSION OF SST FORECASTS The dynamical models in the Columbia Climate School International Research Institute for Climate and Society (IRI) plume continue to predict a weak and a short duration La Niña. Weak La Niña conditions are expected to persist through FMA 2025 and then transition to ENSO-neutral. The IRI dynamical model average and several of the models of the North American Multi-Model Ensemble (NMME) predict an earlier transition to ENSO-neutral in JFM 2025. The CPC ENSO forecast team favors a weak La Niña through FMA, but there is also a 41 percent chance of ENSO-neutral emerging in this season. PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS Dynamical model forecasts from the NMME, the Coupled Forecast System Model Version 2 (CFSv2), and the Copernicus (C3S) multi-model ensemble system were used extensively for the first six leads when they are available, as was the objective, historical skill weighted consolidation and Calibration, Bridging, and Merging (CBaM) guidance, that combines both dynamical and statistical forecast information. Additionally, the official ENSO forecast favors a weak La Niña through FMA 2025. This anticipated weak La Niña signal played a role in the construction of these outlooks. Composites derived from nearest neighbor statistical analysis of recently observed tropical Pacific SST and Equatorial heat anomalies were utilized where appropriate. At later leads, decadal trends in temperature and precipitation were increasingly relied upon in creating the seasonal outlooks. PROGNOSTIC DISCUSSION OF OUTLOOKS - MAM 2025 TO MAM 2026 TEMPERATURE The MAM 2025 Temperature Outlook is very similar to the lead 2 prediction of MAM 2025 released in January 2025. Models continue to reflect a La Niña temperature pattern, and though the teleconnection typically weakens in MAM compared to the previous season (FMA), there are likely to be lagged impacts of the La Niña. An important caveat is that with a weak La Niña we may see periods of increased variability within the season. Above normal temperatures are favored for much of the southern and eastern CONUS, while below normal temperatures are favored for the Northwest to the Northern Plains. Over Alaska, below normal temperatures are indicated for southeastern and southcentral portions of the state, transitioning to above normal temperatures over western and northern portions of the state. The above normal temperatures over northern Alaska, and the southwestern and eastern CONUS, are further supported by above normal trends. EC, due to weak or conflicting signals among tools, is forecast for a significant fraction of the Lower 48 states and portions of Alaska. Shifting into AMJ 2025, impacts of La Niña are expected to wane as ENSO neutral becomes increasingly likely. Below normal temperatures over Alaska and the Northwest into the Plains diminish in favor of EC along much of the northern tier of the CONUS and southeastern Alaska. Above normal temperatures are maintained and/or expanded over parts of the Western CONUS, Southeast, the eastern quarter of the CONUS, and western and northern Alaska given model agreement among NMME and C3S. This pattern is generally maintained through September-November (SON) 2025 with the support of dynamical climate models and decadal trends, with the least coverage of EC forecast over the upper half of the Mississippi Valley during June-August (JJA). Somewhat larger areas of EC are depicted over Alaska during the July-September (JAS) through SON seasons where guidance had weak or conflicting signals. October-December (OND) 2025 and November-January (NDJ) 2025-2026 feature slightly above normal temperatures across much of the CONUS and Alaska given recent decadal trends. The above normal temperatures diminish and shift to the East Coast by December-February (DJF) 2025-2026, with some indication of above normal temperatures over the Southwest in FMA 2026, and a slight tilt toward below normal over parts of the Northern Plains and Northwest in January-March (JFM) 2026. The last 3 leads of this forecast have large areas of EC given comparatively lower confidence at these longer lead times. PRECIPITATION The MAM 2025 Precipitation Outlook reflects the expected La Niña teleconnection over the CONUS. Above normal precipitation is favored over the Northwest, Great Lakes, interior Northeast, Ohio and Tennessee Valleys, portions of the Mississippi Valley, and northern and western Alaska. Below normal precipitation is indicated for the Southwest, much of the Great Plains, the Gulf Coast, and the southern coast of Mainland Alaska. This precipitation pattern is very similar to last month’s Lead 2 outlook for MAM, with only relatively minor adjustments rendered to the depiction. EC is indicated over a significant fraction of the Lower 48 states and much of Alaska south of the Brooks Range. La Niña typically leads to a wetter northern California and drier southern California, however, the impacts of La Niña can generally be quite variable over central parts of the West Coast. In addition, the weakness of this event may add additional uncertainty to the precipitation pattern, as such, probabilities are weak and EC is indicated over much of California. Models had some disagreement over the Northern Plains, with every forecast category obtaining some support from the array of model solutions, thus EC is favored over the Northern Plains as well. While La Niña typically can lead to below normal precipitation over the East Coast, the location of the jet stream and associated storm track over the Great Lakes and interior Mid-Atlantic during a La Niña can be variable. Should it shift more to the east, there may be more precipitation over the East Coast, while shifting more to the west may lead to less precipitation. Given the weakness of the La Niña leading to potentially more variability in the teleconnection pattern vs. during a strong La Niña, EC is favored over the Northeastern coast. Similarly to temperature, we expect some lagged impacts of the La Niña well into MAM 2025, and the forecasted precipitation pattern remains similar to the expected La Niña teleconnection pattern into this season. As the forecast progresses through later leads and into Fall/Winter 2025, ENSO guidance becomes less of a player in this forecast, and decadal precipitation trends are relied on more. Below normal precipitation shifts northward from its more southwestern orientation in MAM through OND 2025. Above normal precipitation shifts from the Great Lakes, Ohio Valley, and Mid-Atlantic toward the East Coast through SON. From May-July (MJJ) through SON, the tilt towards above normal precipitation over the East Coast states is related to the increased climatological influence of tropical cyclones, as well as trends. In Alaska, above normal precipitation over northwestern portions of the state is favored to expand to the south and east as the forecast period progresses. Statistical guidance is increasingly relied upon for later leads, for example NDJ 2025-2026 and on, and small, relatively weak regions of above normal precipitation are favored for the Southeast that shift northward to the end of the forecast period (MAM 2026). Above normal precipitation is also favored over parts of the northern CONUS, while below normal precipitation begins to make an appearance over the Southwest late next winter. Above normal precipitation probabilities persist over Alaska though the remainder of the period, though shift from covering much of the state in OND to the north and east in NDJ and DJF 2025-2026, to the west in JFM, FMA, and MAM 2026. FORECASTER: Anthony Artusa 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 Mar 20 2025 1991-2020 base period means were implemented effective with the May 20, 2021 forecast release. $$