Prognostic Discussion for Long-Lead Seasonal Outlooks NWS Climate Prediction Center College Park MD 830 AM EST Thu Nov 18 2021 SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS The December-January-February 2021-2022 temperature outlook depicts elevated odds of above-normal seasonal mean temperatures for most of the southern half of the U.S. and for the eastern third of the nation. The greatest likelihood for above normal temperatures are located in the Northeast and Southeast. Below normal temperatures are most likely for most of Alaska, the Pacific Northwest, and northern Idaho, Montana, and parts of western North and South Dakota. For precipitation, above-normal seasonal precipitation amounts are favored for the Pacific Northwest, northern Rockies, Great Lakes, and Ohio Valley. Drier than normal conditions are most likely for the southern tier of the U.S. from California eastward to the Southeast. The greatest likelihood of below-normal precipitation is in southern New Mexico, parts of western Texas, and south Florida. La Niña conditions persist in the Pacific Ocean and are forecasted to remain through spring 2022. The influence of La Niña contributed substantially to the temperature and precipitation outlooks through the winter months into Spring 2022. 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 La Niña conditions have strengthened in the Pacific Ocean as indicated by both ocean and atmospheric indicators. The La Niña advisory issued in early October remains in effect for the November forecast, and La Niña conditions are expected to persist through the Northern Hemisphere winter and into spring 2022, followed by enhanced probability of ENSO neutral conditions in late spring through summer. Equatorial Pacific sea surface temperature anomalies are negative from west of the date line to the South American coast with anomalies ranging from -0.7 to -1.0 degrees C. The latest weekly Niño 3.4 region sea surface temperature anomaly was -0.8 degrees C. Negative subsurface temperature anomalies have persisted across the eastern Pacific Ocean for the past two months, though have weakened since mid-October. A reservoir of colder than normal water is observed along the equator from 160W to 90W ranging from 0 to 200 meters in depth, surpassing -0.6 degrees C at the peak from 130W to 120W. Positive subsurface temperature anomalies have expanded from the western Pacific to the central Pacific in recent observations. Current upper ocean heat content remains negative, reflecting La Niña conditions. The expansion of positive subsurface temperature anomalies and slight weakening of the cold reservoir support current La Niña conditions that are forecasted to persist through the winter and weaken into the spring and summer 2022. The atmospheric state remains consistent with La Niña with suppressed convection over the western and central Pacific ocean and enhanced convection observed around Indonesia. Low-level easterly wind anomalies were present over the western and east-central equatorial Pacific Ocean, with upper level westerly wind anomalies observed over the western equatorial Pacific, consistent with La Niña conditions. Below-normal sea surface temperatures are present off the southern and western coasts of Alaska, consistent with the La Niña atmospheric response. Western U.S. sea surface temperatures have shifted to neutral from anomalously cold in mid- to late- October. Neutral to below-normal sea surface temperatures are present in the Gulf Coast and Eastern Seaboard, with anomalously warm sea surface temperatures off the northeastern coast in the Gulf Stream. PROGNOSTIC DISCUSSION OF SST FORECASTS The CPC Niño 3.4 SST consolidation forecast predicts anomalously cold SSTs in DJF 2021-2022 between -1.5 and -2.0 degrees C. The CPC Niño 3.4 SST consolidation forecast predicts that SSTs indicating La Niña conditions continue but weaken though at least MAM, as negative SST anomalies weaken from between -1.5 and -2 degrees C in DJF to above -0.5 degrees C in MAM. The dynamical model sources such as those from the North American Multi-Model Ensemble (NMME) favor a moderate La Niña in DJF with the ensemble mean reaching about -1.5 degrees C. Ensemble spread is large in DJF, with some members predicting a stronger La Niña with SST anomalies nearing -3 degrees C, and others a weaker La Nina with SST anomalies near -0.5 degrees C. The NMME predicts still negative but weakening SST anomalies from DJF, with SST anomalies forecast by the ensemble mean weakening to -0.5 degrees C in MAM. The CPC / IRI official ENSO outlook depicts high probabilities for La Niña (90%) in DJF, decreasing to a 50% probability of La Niña or ENSO Neutral conditions in MAM. AMJ through JJA depict enhanced odds (over 50%) for ENSO neutral conditions. PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS Potential typical impacts known to be associated with La Niña winters are utilized in preparation of the outlook via common techniques that include composite analysis (including consecutive La Niña events) and regressions anchored to Niño 3.4 SST in both diagnostic and prognostic terms. La Niña impacts were considered through the MAM 2022 forecast lead consistent with the expected La Niña evolution. Dynamical model guidance from the NMME and Copernicus (C3S) multi-model ensemble systems are used through AMJ 2022. In addition, objective, skill-based consolidation tools contribute to the outlook and include the ENSO/OCN and a complete suite of statistical/dynamical tool combinations. Statistical guidance such as the global SST based Constructed Analog (CA), CBaM guidance, and long term temperature and precipitation trends played a role in many of the outlook seasons. Coastal SSTs also are considered, especially at the early leads. PROGNOSTIC DISCUSSION OF OUTLOOKS - DJF 2021 TO DJF 2022 TEMPERATURE The DJF 2021-2022 temperature outlook favors above-normal temperatures for most of the southern half and the eastern third of the CONUS. The greatest odds for above-normal temperatures are in the northeast and southeast regions. Below-normal temperatures are most likely for the Pacific Northwest, northern Idaho, Montana, and western North and South Dakota, as well as much of Alaska. These temperatures are reflective of the La Niña base state, trend, and anomalous sea surface temperatures. The expectation of La Niña conditions and associated typical impacts - on average over many events - is the primary driver of the DJF 2021-2022 temperature outlook, and is indicated by multiple methods that includes empirical, statistical and dynamical forecast guidance. Dynamical model guidance (NMME and C3S) favor a response generally consistent with La Niña, though the C3S favors near- to above-normal temperatures in the region of expected below-normal temperatures in the northern CONUS. A wave train typical of La Niña winters is present and amplified in DJF in the NMME, which is consistent with predicted NMME DJF temperatures. Temperature guidance from dynamical and statistical models is strongly cold in Alaska and parts of western Canada, and remains anomalously cold through spring 2022. Dynamical and statistical model guidance reflect the expected DJF pattern of La Niña and trend, and anomalously cold coastal SSTs favor below-normal temperatures in Alaska. The area of enhanced below-normal temperature probabilities in the northern parts of the CONUS decreases in coverage through MAM2022, shifting westward toward the west coast of the U.S. This relaxation of the coverage of favored below-normal temperatures to the west coast through MAM2022 is at odds with the forecast issued in October. Dynamical and statistical model guidance updated in November are slightly warmer further west into the northern Great Plains than previous guidance, and probabilities for below-normal temperatures have been reduced reflective of this shift. Beginning in AMJ2022, equal chances (EC) are indicated in the northwest, shifting to warmer temperatures as the forecast moves into spring and summer. This relaxation of the favored below-normal temperatures is consistent with the waning La Niña signal moving into the spring, and change to ENSO neutral conditions in the summer, where temperature trends will be more dominant. The greatest odds for above-normal temperatures shift from the northeast in MAM2022, as temperature trends become less dominant in the region and dynamical models decrease probabilities for above-normal temperatures. The greatest odds for above-normal temperatures in the southeast shifts towards TX, NM, and AZ in MAM2022, following a typical trend and La Niña pattern that is favored by dynamical model suites. The spatial extent decreases in AMJ2022 as the tropical forcing begins to shift to ENSO neutral conditions. The north-central U.S. favors EC for above and below-normal temperatures, with increasing coverage through AMJ2022, due to uncertainty in tools and the tendency for increased variability or weak signals from tropical forcing. The remaining set of temperature outlooks remain generally the same from the October release and are based on the ENSO/OCN and other consolidation forecast tools for which long term temperature trends contribute significantly at times in various regions PRECIPITATION For the DJF 2021-2022 precipitation outlook, above-normal seasonal precipitation amounts are most likely for the west coast of Alaska, the Pacific northwest, northern Rockies, and portions of the Great Lakes, Ohio Valley, and Northeast. Above-normal Great Lakes water temperatures lead to enhanced possibility of lake effect precipitation and contributed to the higher probability of above-normal precipitation over the Great Lakes region (40%) in DJF 2021-2022 through FMA2022. Enhanced probabilities of above-normal precipitation in the Pacific NW is largely based on composite analysis of La Nina winters. Drier than normal conditions are most likely for south-central Alaska and along the southern tier of the CONUS. The highest probability of below-normal precipitation (50%) in DJF 2021-2022 is found in southern Arizona and New Mexico, parts of western Texas, and south Florida, consistent with dynamical model guidance favoring enhanced probability of below-normal precipitation in these regions. The evolution of precipitation outlooks through MAM 2022 are derived from the typical observed impacts during La Niña winters, and statistical and dynamical model guidance. Given the predicted weakening of La Niña conditions to ENSO neutral conditions in AMJ 2022, the AMJ 2022 precipitation outlook is derived from dynamical and statistical model guidance. The remaining set of outlooks are primarily based on the forecast consolidation of statistical guidance and long term precipitation trends and remain similar to the forecasts issued in October. FORECASTER: Johnna Infanti 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 Dec 16 2021 1991-2020 base period means were implemented effective with the May 20, 2021 forecast release. $$