Weather
The NOAA recently released its outlooks for summer 2024: June, July, and August. Below-normal temperatures are expected for parts of Alaska and the northern central U.S., while above-normal temperatures are likely for most other areas. Below-normal precipitation is expected in the western U.S. but above-normal precipitation in parts of the eastern U.S. and Alaska.
Below is an AI-generated summary for those unfamiliar with meteorological terms, followed by the full NOAA discussion.
Temperature Outlook
Alaska
- Southwestern Coast and Alaska Peninsula: Below-normal temperatures are expected, supported by dynamical model forecasts and below-average sea surface temperatures near the coast.
- Eastern Alaska: Above normal temperatures are likely, according to most dynamical model forecasts and the consolidation.
Continental United States (CONUS)
Western CONUS: Above-normal temperatures are favored for most areas, with probabilities exceeding 60% for parts of the Southwest. This is supported by the consolidation, related to significant decadal trends in summer temperatures, and reinforced by a below-normal precipitation forecast.
California Coast: Probabilities favoring above-normal temperatures are reduced, as models predict potential below-normal temperatures in June.
Southern Great Plains and Eastern CONUS: Most forecast tools favor above-normal temperatures across the southern half of the Great Plains and most of the eastern CONUS.
Northern Central CONUS: Equal chances (EC) of above, below, or near normal temperatures are forecast. Some models indicate the potential for below-normal temperatures, and positive soil moisture anomalies may help maintain below or near-normal temperatures early in the season.
Precipitation Outlook
Alaska
- Most of Alaska (excluding the western Aleutians and Southeast Alaska): Above-normal precipitation is favored, and dynamical models predict southerly flow into the state.
Continental United States (CONUS)
- Western CONUS (excluding climatologically drier regions of California, Nevada, and Arizona): Below normal precipitation is favored, supported by most tools and the consolidation, and consistent with potential early impacts of La Niña in some areas.
- Gulf Coast Region, Lower Mississippi Valley, Ohio Valley, Mid-Atlantic, and Southern New England: Above normal precipitation is favored, consistent overall with the precipitation consolidation, decadal trends, and potential early tropical activity related to La Niña and above average tropical sea surface temperatures.
Prognostic Discussion for Long-Lead Seasonal Outlooks NWS Climate Prediction Center College Park MD 830 AM EDT Thu May 16 2024 SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS At present, an El Niño Advisory remains in effect but atmospheric and oceanic patterns associated with El Niño are decreasing. El Niño Southern Oscillation (ENSO) neutral conditions are expected for the April-May-June (AMJ) season as a whole, and there are approximately even chances of ENSO neutral or La Niña conditions by the June-July-August (JJA) season. A La Niña climate state is more likely to develop by July-August-September (JAS) with a probability of almost 70 percent, and would be expected to continue through winter, once in place. The JJA 2024 temperature outlook favors below-normal temperatures for the southwestern coast of Mainland Alaska, while above-normal temperatures are favored for central and eastern Alaska. Above-normal temperatures are likely for the western Contiguous U.S. (CONUS) and across the Southern Plains into the western Gulf Coast region. Above-normal temperatures are also favored for the eastern CONUS with probabilities for above-normal temperatures exceeding 50 percent for the Northeast. Equal Chances (EC) of below, near, and above-normal seasonal mean temperatures are indicated for parts of the northern central CONUS. The JJA 2024 precipitation outlook slightly favors above-normal precipitation across most of Alaska. The outlook favors below-normal precipitation across most of the West from the Pacific Coast across the Rocky Mountains, while EC is predicted for the climatologically drier region over California, Nevada, and Arizona. Above-normal precipitation is favored for a large area of the eastern CONUS stretching from the Gulf Coast northeastward across the Lower Mississippi Valley and the Southeast, into the Ohio Valley, Mid-Atlantic, and southern New England. For the remaining areas of the central CONUS, where possible seasonal total precipitation amounts are predicted to be similar to climatological probabilities, EC is forecast. 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 Although the current interannual climate state is El Niño, as represented by the most recent seasonal mean Niño 3.4 index value of +1.1 degrees Celsius, the most recent weekly mean sea surface temperature (SST) anomaly for the Niño 3.4 region is only +0.3 C, as the equatorial Pacific is cooling. A substantial reservoir of colder than average ocean temperatures remains below the surface near the Date Line at a depth of 100 to 200 meters extending into the Eastern Pacific at a depth of about 150 meters to the surface. Negative SST anomalies are observed near the equator in the east-central Pacific with anomalies exceeding -1.0 degrees C in some locations. Outgoing longwave radiation (OLR) anomalies are weak across the tropical Pacific indicating near average convection and precipitation. Low-level (850-hPa) winds were near average over most of the tropical Pacific Ocean. Cross equatorial upper-level (200-hPa) wind anomalies were observed near the Date Line and over east-central equatorial Pacific. Most recent, short term, atmospheric and oceanic anomalies are more indicative of ENSO neutral conditions than the current El Niño interannual state. Significant increases in soil moisture were observed in the last four weeks over the north-central CONUS, and positive soil moisture anomalies are observed over much of the region. Positive SST anomalies are currently observed along the Gulf Coast and near the Atlantic Coast of the Southeast. SST anomalies are near average along most of the West Coast. Negative SST anomalies are observed along the west coast of Mainland Alaska. Surface boundary conditions, such as soil moisture anomalies, and near coastal SST anomalies can influence local temperature and precipitation over the next season. Soil moisture anomalies have a greater influence on surface temperatures over the Great Plains in the summer months. PROGNOSTIC DISCUSSION OF SST FORECASTS SST forecasts from most North American Multi-Model Ensemble (NMME) dynamical models and from most statistical models, including the CPC Constructed Analog (CA) and Canonical Correlation Analysis (CCA) predict increasingly negative average SST anomalies for the Niño 3.4 region through the coming seasons into next winter. Some individual models of the NMME and of the International Multi-Model Ensemble (IMME or C3S) favor ENSO neutral SSTs in the Niño 3.4 region through autumn, while the consolidated NMME models indicates approximately a -1.1 degree C anomaly, considered to be a moderate La Niña event. The CPC Niño 3.4 SST consolidation forecast predicts a peak anomaly of -1.1 degrees C for the November-December-January (NDJ) season. The CPC ENSO Outlook predicts greater than an 80 percent chance of La Niña forming by meteorological boreal autumn, September-October-November (SON), and continuing through winter into early 2025. PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS The seasonal temperature and precipitation outlooks are based primarily on forecast tools derived from the NMME, including calibrated versions, such as the Probability Anomaly Correlation (PAC) and the Calibration, Bridging and Merging (CBaM), which calibrates the dynamical model forecast using Bayesian Joint Probability (BJP) models, as well as generating statistical or “bridging” BJP models of temperature and precipitation from dynamical model Niño 3.4 anomaly forecast predictors. An ENSO-OCN forecast tool is used to represent the combined influence of the El Niño Southern Oscillation (ENSO) and decadal timescale trends in temperature and precipitation, using the Optimum Climate Normal (OCN). La Niña impacts are considered in the outlooks from JJA 2024 through March-April-May (MAM) 2025, with La Niña impacts possible late in the JJA 2024 season despite equal chances of ENSO neutral or La Niña for the season as a whole. Longer lead outlooks, beginning in April-May-June (AMJ) 2025 are based primarily on decadal temperature and precipitation trends . A consolidation of multiple statistical and dynamical forecast tools that utilizes PAC calibration is used throughout the outlooks from JJA 2024 to JJA 2025. PROGNOSTIC DISCUSSION OF OUTLOOKS - JJA 2024 TO JJA 2025 TEMPERATURE The JJA 2024 seasonal temperature outlook favors below normal temperatures for the southwestern coast of Mainland Alaska and the Alaska Peninsula, supported by dynamical model forecasts from the NMME and below average SSTs near the coast. Above normal temperatures are favored for eastern Alaska as in most dynamical model forecasts and the consolidation. Above normal temperatures are likely for most of the western CONUS, with probabilities exceeding 60 percent for parts of the Southwest, supported by the consolidation, related to significant decadal trends in summer temperatures and reinforced by a below normal precipitation forecast. Probabilities favoring above normal temperatures are reduced for the California coast, where models predict potential below normal temperatures in June. Above normal temperatures are favored across the southern half of the Great Plains and for most of the eastern CONUS in the JJA 2024 seasonal outlook, in agreement with most forecast tools. EC is forecast for the northern central CONUS, where some models such as the CBaM indicate the potential for below normal temperatures, and positive soil moisture anomalies may help maintain below or near normal temperatures, early in the season. The temperature outlooks for the next two seasons, through summer into early autumn, favor above normal temperatures across the entire CONUS, driven by strong decadal temperature trends in these seasons, and lesser impacts of a potential La Niña. The temperature outlook for Alaska during this period favors below normal temperatures for parts of southern Alaska and above normal temperatures for northern Alaska, influenced by La Niña and decadal trends , respectively. This temperature pattern essentially continues in the outlooks for Alaska into early spring of 2025, as La Niña is predicted to continue, after which, above normal temperatures are increasingly favored for Alaska at longer leads, related to decadal trends . A more canonical La Niña temperature pattern is favored over the CONUS from late autumn through winter, with below normal temperatures favored for parts of the Pacific Northwest from NDJ 2024-2025 through MAM 2025, and above normal temperatures more likely across the southern tier of the CONUS, including most of the Southwest, the Gulf Coast, and the Eastern Seaboard. Decadal temperature trends favor above normal temperatures across most of the CONUS for the longer leads, excluding parts of the northern central CONUS, where trends are weaker. PRECIPITATION The JJA and JAS seasonal precipitation outlooks favor above normal precipitation for most of Alaska, excluding the western Aleutians and Southeast Alaska, with dynamical models predicting southerly flow into the state. Below normal precipitation is favored for most of the western CONUS, excluding only climatological drier regions of California, Nevada and Arizona, supported by most tools and the consolidation, and consistent with potential early impacts of La Niña in some areas. Above normal precipitation is favored from the Gulf Coast region across the Lower Mississippi Valley, the Ohio Valley, Mid-Atlantic, and southern New England, consistent overall with the precipitation consolidation, decadal trends , and potential early tropical activity related to La Niña and above average tropical SSTs. The next several seasonal precipitation outlooks indicate an evolution of the precipitation pattern over the CONUS, shifting areas of favored below normal precipitation southward away from the northern tier and west coast, and eastward towards the Mississippi Valley. Above normal precipitation is favored over the Northwest by the September-October-November (SON) season into winter, consistent with a predicted La Niña. During the winter season, areas of favored above normal precipitation shift eastward into the Northern Plains and southeastward into the central Mississippi and Ohio Valleys. Winter into early spring seasonal outlooks favor below normal precipitation across much of the southern tier of the CONUS from Southern California and the Southwest to the Gulf Coast and Southeast and for the south coast of Alaska, following a canonical La Niña precipitation pattern, as represented by regressions of precipitation onto Niño 3.4 SST anomalies. The last three precipitation outlooks favor below normal precipitation for parts of the northwestern CONUS, due to decadal trends favoring drier conditions. Beginning in October-November-December (OND) 2024 through all longer leads, above normal precipitation is favored for parts of the North Slope of Alaska, due to positive decadal trends in precipitation and adjacent SSTs. FORECASTER: Dan Collins 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 Jun 20 2024 1991-2020 base period means were implemented effective with the May 20, 2021 forecast release. $$
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