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. 
$$