FXUS05 KWBC 201231 PMD90D Prognostic Discussion for Long-Lead Seasonal Outlooks NWS Climate Prediction Center College Park MD 830 AM EDT Thu Oct 20 2022 SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS The November-December-January 2022-2023 temperature outlook depicts elevated odds for above-normal seasonal mean temperatures for western Alaska, much of the western U.S. to include the central Great Basin, central and southern Rockies, and Southwest, eastward to include much of the central and southern Great Plains, areas of the Southeast and along the Atlantic seaboard. The greatest likelihood for warmer than normal temperatures is for the Southwest and southern Great Plains. For precipitation, above-normal seasonal precipitation amounts are favored for the west coast of Alaska, the Pacific Northwest and the northern Rockies. Drier-than-normal conditions are most likely along the southern tier of the U.S. from California eastward to the southern Plains and Southeast with the greatest likelihood for southern Texas. Areas depicted in white and labeled "EC" (Equal-Chances) are regions where climate signals are weak and so there are equal odds for either above-, near- or below-normal seasonal mean temperatures and total precipitation amounts. La Nina conditions remain in place in the Pacific Ocean and its influence continues to contribute to the temperature and precipitation outlooks through the upcoming winter months into early Spring 2023. 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 Nina conditions have remained in place throughout the summer and into the autumn months of 2022 in the Pacific Ocean as indicated by both ocean and atmospheric indicators and a La Nina Advisory remains in effect. Equatorial Pacific ocean surface temperature departures are negative from just west of the Date Line to the South American coast with anomalies in many areas at or less than -1.0 degrees C with some locations in the eastern Pacific reaching -1.5 degrees C or less. The latest weekly Nino4 and Nino3.4 region SST departures were -1.1 and -0.8 degrees C respectively. A strong reservoir of colder than normal water is observed via ocean temperatures along the equator from 155 W to 90 W at a depth ranging from near the surface to 200 meters depth in the east-central Pacific. The negative ocean temperature anomalies in this area range from -4.0 to -6.0 degrees C in some places. This colder than average water supports maintenance of La Nina conditions in the equatorial Pacific into the winter months. The atmospheric state is displaying characteristics quite consistent with La Nina with enhanced convection on average in proximity to Indonesia and suppressed convection near the Date Line. Trade winds are considerably enhanced and upper-level westerly wind anomalies are present in the central Pacific with symmetric cyclonic circulations both north and south of the equator. Large areas of above-normal sea surface temperatures (SSTs) reside in both the north Pacific and north Atlantic oceans. More local coastal SSTs are above-normal for coastal waters near the northwest coast of Alaska as well as the entire West coast of the CONUS. Anomalous SSTs along the east coast are more mixed at the current time. PROGNOSTIC DISCUSSION OF SST FORECASTS The CPC Nino3.4 SST consolidation forecast shows a nearly steady trend through DJF 2022-2023 of near -1.0 degrees C with the CA, Markov statistical models colder during this period and the NMME ensemble mean and CCA predictions warmer during this period. Thereafter, the consolidation forecast and all guidance forecasts a trend of less negative anomalies over time into ENSO neutral territory by the MAM or AMJ 2023 seasons. There is somewhat remarkable agreement and low spread in the forecast tools at this lead (AMJ 2023) as compared to the two preceding La Nina events. The CPC / IRI official ENSO outlook depicts high probabilities for La Nina - greater than 85% and 75% through NDJ and DJF 2022-2023 respectively. Thereafter by FMA 2023, ENSO neutral becomes the most favored category and this continues through MJJ 2023. PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS Potential common impacts known to be associated with La Nina winters are utilized in preparation of the outlook via standard techniques that include composite analysis (including consecutive La Nina events) and regressions anchored to Nino3.4 SST in both diagnostic and prognostic terms. La Nina impacts are considered through the MAM 2023 forecast lead. Statistical guidance, particularly the global SST based CA, played a considerable role along with long term temperature and precipitation trends (OCN) for many leads. Dynamical model guidance from the NMME and Copernicus (C3S) multi-model ensemble systems are utilized through MAM 2023. In addition, objective, historical skill-based consolidation tools contribute to the outlook and include the ENSO/OCN and the complete suite of statistical/dynamical tool combinations. Coastal anomalous SSTs are also considered especially at early leads. PROGNOSTIC DISCUSSION OF OUTLOOKS - NDJ 2022 TO NDJ 2023 TEMPERATURE The NDJ 2022-2023 temperature outlook favors above-normal temperatures for much of the western U.S. eastward to include much of the central and southern Great Plains, areas of the Southeast and also along the Atlantic seaboard. The expectation of La Nina conditions and enhanced odds for associated common impacts - on average over many events - is a primary driver of the evolution of the temperature outlooks from NDJ 2022-2023 through the MAM 2023 lead. Multiple types of guidance was utilized for this assessment and included La Nina composites, ENSO regression / correlation information, statistical forecast tools and dynamical model forecasts. Although some of the participant models within the NMME and C3S suite maintained the colder signature starkly shown in last month's data typically associated with La Nina in areas of Alaska, Canada and the northern U.S., in general, the NMME overall ensemble mean probabilities are considerably warmer in this month's set of forecasts. For many of these areas in the U.S. and southern Canada, however, calibration based on historical forecast skill dramatically decreased probabilities and so confidence is low. Moreover, further inspection of 200-hPa height information from the NMME suite indicated that anomalous positive heights forecast at higher latitudes last month are reduced in this months forecast with a weaker mean Hudson Bay trough in the warmer NMME solutions. This strongly hints at a considerable change in the forecast AO phase over the winter months. Predictability of the seasonal AO phase is low. Given the reasons and associated uncertainty noted above, along with large areas of positive SST anomalies in both the north Pacific and Atlantic, incorporated in the CA statistical guidance, there was not significant changes at this time to the favored below-normal temperature forecast evolution from DJF 2022-2023 through MAM 2023 despite the warmer overall NMME solution this month. The official outlooks over time increase coverage of below-normal temperatures for the Pacific Northwest eastward to the northern Plains and western Great Lakes in DJF 2022-2023 and JFM 2023 and relax this area northward (less coverage and lower probabilities) in FMA and MAM 2023. A forecast for elevated odds of overall colder conditions for the Northeast is implied in the outlooks from NDJ 2022-2023 through FMA 2023. La Nina events are often characterized by high subseasonal variability especially for the north-central CONUS, Ohio Valley and Northeast as these areas are strongly impacted by variations in the AO/NAO and potential stratospheric influences (typically more likely during the second half of winters) - all of which are very difficult to reliably predict at these lead times. Consequently, the coverage of Equal-Chances (EC) is large in some of these areas from JFM to MAM 2023. The greatest odds for above-normal temperatures slowly shifts from the Southwest to the Southeast over the period from NDJ 2022-2023 to FMA 2023 with a minimum in both probabilities and coverage in the southern Plains during the JFM 2023 season. For Alaska, enhanced chances for below-normal temperatures for southeast Alaska and the Alaska Panhandle are introduced in DJF 2022-2023 and maximize in JFM 2023 before decreasing and timing off after MAM 2023. Anomalously positive ocean surface temperatures tilt the odds for above-normal temperatures for parts of the west coast of Alaska through JFM 2023. Odds for favored above-normal temperatures are increased for the south-central southern Plains during MAM, AMJ and MJJ 2023 from the previous set of outlooks due to severe drought conditions currently ongoing and with the prospects for below-normal winter precipitation. If realized, this increases odds for above-normal temperatures during the spring and early summer months. The remaining set of temperature outlooks remain generally the same from the September 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 NDJ 2022-2023 precipitation outlook, above-normal seasonal precipitation amounts are most likely for the west coast of Alaska, the Pacific Northwest and northern Rockies. Drier-than-normal conditions are most likely for the southern tier of the U.S. from southern California eastward to the southern Plains and Southeast. Similar to that described above for temperature, the evolution of the precipitation outlooks through MAM 2023 are anchored to first order from potential typically observed impacts during La Nina winters - on average over many events. The greatest odds for below-normal precipitation during NDJ and DJF 2022-2023 are positioned primarily for southern Texas. In addition, consolidation of both statistical and dynamical model guidance (NMME, C3S) modified the base state La Nina favored impacts and this approach was primarily followed in the outlooks through MAM 2023. Long term precipitation trends, especially positive (more wet) trends in numerous areas in the Midwest and eastern CONUS, contributed to the outlooks over this forecast period as well. The later set of outlooks are primarily based on long term precipitation trends. FORECASTER: Jon Gottschalck 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 Nov 17 2022 1991-2020 base period means were implemented effective with the May 20, 2021 forecast release. $$