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HOME> Outlook Maps>Seasonal Forecast Discussion |
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Prognostic Discussion for Long-Lead Seasonal Outlooks NWS Climate Prediction Center College Park MD 830 AM EDT Thu Jun 16 2022 SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS The July-August-September (JAS) 2022 temperature outlook favors above-normal seasonal mean temperatures across a majority of the U.S. The largest probabilities (more than 60 percent) of above-normal temperatures are forecast for New England and parts of the West. The JJA precipitation outlook depicts elevated probabilities of above-normal precipitation for parts of the East, Southwest, and Alaska, while below-normal precipitation is more likely across much of the Great Plains, western Corn Belt, upper Mississippi Valley, and the northern to central Rockies. Equal chances (EC) are forecast in areas where the likelihood of seasonal mean temperatures or seasonal accumulated precipitation amounts are expected to be similar to climatological probabilities. A La Niña advisory remains in effect and equatorial sea surface temperatures (SSTs) are below average across the central and eastern Pacific Ocean, and the tropical Pacific atmosphere is consistent with a La Niña. La Niña is favored to continue through the Northern Hemisphere summer (52% chance in JAS 2022), with slightly increased probabilities throughout the Northern Hemisphere fall and early winter 2022 (58-59% chance). 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 Oceanic and atmospheric observations across the equatorial Pacific remain consistent with La Niña conditions. The observed weekly SSTs, centered on June 8, feature negative anomalies throughout the central and eastern equatorial Pacific with the largest negative anomalies of -0.5 to -1 degrees C generally from the Date Line to 120W. These negative anomalies have weakened since early May. Subsurface temperature anomalies (averaged between 180 to 100 degrees W and 0-300m depth) also weakened during the spring with values approaching zero. From May 13 to June 7, low-level easterly and upper-level westerly wind anomalies persisted. Suppressed convection continued over the western and central Pacific, while convection was near average or slightly enhanced across parts of Indonesia. Multiple atmosphere Kelvin waves crossed the global tropics throughout this past spring. More recently during late May into the beginning of June, the Real-time Multivariate Madden Julian Oscillation (RMM) index depicted a slower moving and developing Madden Julian Oscillation (MJO) event. However, the propagation of this MJO stalled over the Western Hemisphere during early to mid-June and the amplitude of the RMM index decreased. As of June 15, GEFS and ECMWF ensemble spread is very large on the MJO evolution during the next two weeks. Therefore, forecast confidence is low on how much, if any, the MJO modulates tropical cyclone development across the East Pacific and Atlantic basins during the latter half of June and heading into July. Positive SST anomalies, surrounding Alaska, have increased in magnitude since late May with the largest anomalies (more than +2.5 degrees C) observed along coastal southwestern Alaska. Following a prolonged period of anomalously cold SSTs along the West Coast, SSTs are now near average. Positive SST anomalies continued across the northern Gulf of Mexico and coastal waters from the Mid-Atlantic northward to New England. PROGNOSTIC DISCUSSION OF SST FORECASTS The CPC SST Consolidation for the Nino 3.4 region indicates a slight decrease in the magnitude of the negative anomalies this summer, followed by a decline to between -0.5 and -1 degrees C during the fall season. The spread among the statistical tools is large this fall, with outcomes ranging from slightly positive (CCA) to a moderate strength La Niña (constructed analog). The NMME maintains a La Niña with negative anomalies at or below -0.5 degrees C persisting through DJF 2022-2023. Since the observed oceanic and atmospheric anomalies have weakened recently, uncertainty is high on whether La Niña may transition to ENSO-neutral conditions this summer. As of early June, the CPC/IRI consensus forecast calls for a 52 percent chance of La Niña during July-August-September before slightly increasing to around 58 percent through the fall and early winter. PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS Tools used for the seasonal outlooks included dynamical model guidance such as the North American Multi-Model Ensemble (NMME), the Calibration, Bridging, and Merging (CBaM) version of the NMME, and the Copernicus International Multi-Model Ensemble (C3S). Current soil moisture conditions played a role in the JAS temperature outlook, primarily across the Great Plains and Southwest. The consolidation tool, which includes NMME input and various statistical tools, was used more extensively beyond lead 5, NDJ. La Niña composites were considered through next winter since La Niña is the most likely outcome. Decadal trends in temperature and precipitation were a factor at all time leads but relied upon the most during the spring and summer 2023. PROGNOSTIC DISCUSSION OF OUTLOOKS - JAS 2022 TO JAS 2023 TEMPERATURE A broad coverage of above-normal temperatures is favored throughout much of the U.S. during JAS, but probabilities vary regionally. Along the East Coast, above-normal temperatures are most likely for New England due to: excellent agreement among tools including the inputs to the NMME, decadal temperature trends, and large positive SST anomalies nearby. Due to recent heavy rainfall, anomalously wet soil moisture is now present across southeast Kansas, northeast Oklahoma, and the Ozarks region. This was a contributing factor to a weakness in the probabilities for above normal temperatures for parts of the central CONUS along with the latest calibrated NMME and neutral decadal trends during mid to late summer. The NMME and C3S support large probabilities for above normal temperatures, centered across Utah and western Colorado, with probabilities decreasing to the south which is consistent with the JAS precipitation outlook slightly favoring an enhanced Monsoon. EC is forecast for parts of the northern Great Plains, based on anomalously wet soil moisture and the NMME forecast. EC is also forecast for parts of the Pacific Northwest where the July outlook is slightly favoring below-normal temperatures and is supported by the calibrated NMME. Above-normal temperatures are slightly favored for Mainland Alaska, although forecast confidence is relatively low given weak signals among the tools and lack of skill recently. Beginning in the fall 2022 and through winter 2022-2023, minor changes were made to the previous outlook, released on May 19. These modifications were based on the latest dynamical model solutions and La Niña composites. During the spring and summer 2023, the temperature outlook is generally consistent with decadal trends . PRECIPITATION For a majority of the CONUS and Alaska during JAS, either EC or limited probabilities (below 40 percent) for below or above-normal precipitation are forecast due to very weak signals in the calibrated NMME. Based on a consensus between the latest dynamical models and La Niña precipitation composites, below-normal precipitation is most likely for the north-central Rockies, much of the Great Plains, and the western Corn Belt. The week-2 dynamical models , which cover the last week of June, are consistent that low to mid-level moisture is likely to increase across the Southwest due to southeasterly flow. Week 3-4 dynamical models , valid for the first half of July, depict a favorable position of the 500-hPa ridge axis for enhanced monsoon rainfall. Based on these factors for a robust start to the Monsoon, the July precipitation outlook, and the typical inverse relationship in Monsoon rainfall following a dry winter, above-normal precipitation is favored for the Desert Southwest. The favored area of wetness along parts of the East and Gulf Coasts is consistent with the outlook for a 65 percent chance of an above-normal Atlantic hurricane season. Also, decadal trends support the largest probabilities for above-normal precipitation across the Mid-Atlantic and parts of the Northeast. Many of the dynamical model tools support a small tilt for above-normal precipitation across the central interior of Mainland Alaska. Since probabilities for La Niña conditions are near 60 percent during the late fall and winter, a slightly favored area for below-normal precipitation was added to the southern tier of the CONUS. During the spring and summer 2023, the precipitation outlooks are based mostly on decadal trends . 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 Cas e 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 Jul 21 2022 1991-2020 base period means were implemented effective with the May 20, 2021 forecast release. $$
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