Prognostic Discussion for Long-Lead Seasonal Outlooks NWS Climate Prediction Center College Park MD 830 AM EST Thu Jan 18 2024 SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS El Niño conditions continue with equatorial sea surface temperatures (SSTs) above average across the central and eastern equatorial Pacific Ocean. The atmospheric response across the global tropics is consistent with the ongoing El Niño. El Niño is forecast to persist through March-April-May with a transition to ENSO-neutral conditions later in the spring and summer. The February-March-April (FMA) 2024 temperature outlook favors above-normal temperatures across the Pacific Northwest, northern to central California, parts of the Great Basin, northern Rockies, northern Great Plains, Great Lakes, and Northeast. The highest forecast confidence for above-normal temperatures exists for the Pacific Northwest and much of Alaska. Below-normal temperature probabilities are slightly elevated across southeastern New Mexico and western to central Texas. Near-normal temperatures are favored for much of the Southeast. The FMA 2024 precipitation outlook depicts elevated probabilities for above-normal precipitation for southern California, the desert Southwest, the central to southern Plains, the Southeast, and much of the East Coast. The Southeast is the most likely area to have above-normal precipitation. Above-normal precipitation is also favored for parts of southern Alaska and the North Slope of Alaska. Below-normal precipitation is favored for the Pacific Northwest and from the Great Lakes south to the Ohio Valley. Areas depicted in white and labeled “Equal-Chances” or “EC” are regions where climate signals are weak, and so there are equal chances for either above-, near- or below-normal seasonal mean temperatures or total precipitation amounts. 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 Above-average SSTs persist across the equatorial central and eastern Pacific. Weekly observed SST anomalies in the Niño 3.4 region are at +1.9 degrees Celsius. Subsurface temperature anomalies (averaged from 180-100W and 0-300 meters) are at +1.0 degrees Celsius which is a decrease from a peak of +1.5 degrees Celsius in late November. This slight decrease is due to an expansion of negative subsurface temperature anomalies eastward to 150W, but these negative anomalies remain at a depth of 100 meters. From December 16, 2023 to January 10, 2024, positive OLR anomalies (suppressed convection and precipitation) continue over the Philippines, Indonesia, and northern Australia. Negative OLR anomalies (enhanced convection and precipitation) were observed around the Date Line and extend through the eastern tropical Pacific, mostly to the north of the equator. Low-level (850-hPa) wind anomalies were westerly over the east-central equatorial Pacific and easterly across the far western Pacific. Upper-level (200-hPa) wind anomalies were easterly over the eastern equatorial Pacific. These atmospheric and oceanic conditions reflect a continuation of El Niño. The Madden-Julian Oscillation (MJO) remains active and was strong enough to rapidly weaken the positive phase of the Indian Ocean dipole and also enhance the convection across the western Maritime Continent during early January. The GEFS and ECMWF models are in excellent agreement that the MJO propagates eastward to the West Pacific during late January. By the end of the month and heading into February, the MJO is likely to constructively interfere with El Niño. PROGNOSTIC DISCUSSION OF SST FORECASTS The CPC SST consolidation forecast for Niño 3.4 depicts decreasing positive anomalies by the spring, and it is typical for El Niño to peak in strength during the winter. Dynamical and statistical models are in good agreement that a transition to ENSO-neutral conditions occurs either in the spring or by the early summer. The CPC ENSO outlook indicates a likely transition to ENSO-neutral during April-May-June with increasing chances of La Niña from the summer into the fall. By August-September-October, there is more than a 60 percent chance of La Niña. PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS The temperature and precipitation outlooks for FMA 2024 were based on dynamical model guidance such as the North American Multi-Model Ensemble (NMME), International Multi-Model Ensemble (IMME), and statistical tools such as the global SST-based Constructed Analog (CA) and ENSO-OCN. The objective, historical skill-weighted consolidation was a major tool used in the outlooks, and that includes the ENSO-OCN tool and a complete suite of statistical and dynamical tool combinations. El Niño composites were used primarily during FMA and to a lesser extent through MAM as the atmospheric response to El Niño is expected to diminish later in the spring. La Niña composites were considered beginning during the summer and using these composites, modifications were made to the late fall 2024 and winter 2024-2025 outlooks. Long-term climate trends were considered for all leads, but were relied upon most from the summer 2024 through FMA 2025. PROGNOSTIC DISCUSSION OF OUTLOOKS - FMA 2024 TO FMA 2025 TEMPERATURE Elevated probabilities of above-normal temperatures during FMA 2024 are forecast across the northern tier of the contiguous U.S. (CONUS) and Alaska which is supported by the calibrated NMME, consolidation tool, and El Niño composites. The largest probabilities (above 50 percent) for above-normal temperatures are forecast for much of Oregon, Washington, and northern Idaho where the teleconnection to El Niño has its strongest correlation. Above-normal temperature probabilities are limited to below 40 percent across the Northern Great Plains and parts of the Upper Midwest due to uncertainty on the Arctic Oscillation (AO) phase. A persistent -AO could promote a major Arctic air outbreak which could skew the seasonal mean temperature towards at least the middle tercile for these areas. In addition, the Madden-Julian Oscillation has remained active since November 2023. If the MJO remains active and results in subseasonal pattern changes, that would also lead to lower forecast confidence. Despite the increased uncertainty related to the AO and MJO, above-normal temperatures remain the most likely outcome across the north-central CONUS given the ongoing El Niño. Based on El Niño composites and the ENSO-OCN tool along with continuity from previous outlooks, below-normal temperature probabilities are elevated across southeastern New Mexico and western to central Texas. The expectation of a highly variable temperature pattern during FMA along with support from the consolidation tool leads to near-normal temperatures being favored for much of the Southeast. Equal chances (EC) for below, near, or above-normal temperatures are forecast for parts of the southern tier of the CONUS due to conflicting and/or weak signals among the statistical and dynamical tools. Long-term trends became the major factor in the temperature outlook during the summer. Given the increasing chance of La Niña by the late summer and fall, La Niña temperatures composites were also considered. PRECIPITATION The FMA precipitation outlook is consistent with El Niño composites and strongly favors above-normal precipitation across the Southeast with below-normal precipitation more likely from the Ohio Valley north to the Great Lakes. Based on good agreement among statistical and dynamical tools, the largest probabilities (more than 60 percent) for above-normal precipitation are forecast across north-central Florida. Slightly elevated above-normal precipitation probabilities extend north along the East Coast to southern New England and also westward to parts of the Great Plains, based on El Niño composites and the IMME. Dynamical models and statistical tools support increased below-normal precipitation probabilities across the Pacific Northwest and northern Intermountain West. Although the NMME trended drier from its December model run throughout the Southwest and California, above-normal precipitation is favored for these areas due to support from the consolidation tool and El Niño composites. Based on the consolidation tool, NMME, and ENSO-OCN, increased above-normal precipitation probabilities are forecast for much of southern Alaska and the North Slope of Alaska. The March-April-May precipitation outlook maintained continuity from the previous month with El Niño expected to have a lingering influence into at least the early spring. By April-May-June (AMJ), the NMME depicts an increasing dry signal across the southern Great Plains and the AMJ outlook followed this model guidance. Minor adjustments were made to subsequent three-month periods through the summer, consistent with the updated NMME, consolidation, and long-term trends. Given the increasing chance of La Niña by the late summer and fall, later outlooks were tilted towards La Niña precipitation composites. FORECASTER: Brad Pugh 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 Feb 15 2024 1991-2020 base period means were implemented effective with the May 20, 2021 forecast release. $$