Prognostic Discussion for Long-Lead Seasonal Outlooks 
NWS Climate Prediction Center College Park MD 
830 AM EDT Thu Jun 20 2024 
 
SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS 
 
The final El Niño Advisory was recently issued in the 17 June 2024 El Niño 
Southern Oscillation (ENSO) Outlook. Currently, ENSO-neutral conditions are 
present with equatorial sea surface temperatures (SSTs) above average in the 
west-central Pacific Ocean, near average in the east-central Pacific Ocean, and 
below-average in the far eastern Pacific Ocean. A La Niña watch is now in 
effect as La Niña is favored to develop during July-September (JAS, 65% chance) 
and persist into the Northern Hemisphere winter 2024-25 (85% chance during 
November-January, NDJ). 
 
The JAS 2024 Temperature Outlook favors above normal temperatures for much of 
the contiguous United States (CONUS), with the strongest probabilities reaching 
70 to 80% over parts of the four corners region. Enhanced probabilities of 
above normal temperatures reaching 60 to 70% are found over the Gulf Coast. In 
contrast, equal-chances (EC) of above, near, and below normal temperatures are 
favored over the west coast of the CONUS. Below normal temperatures are 
indicated over southwestern Alaska, transitioning to above normal over the 
northeast part of the state. 
 
Below normal precipitation is favored over parts of the western and central 
CONUS in JAS 2024, excepting over the West Coast where EC is favored. Above 
normal precipitation is forecast for southeastern Texas, the Gulf States, and 
along the Eastern Seaboard into New England with the highest probabilities (50 
to 60%) along parts of the Gulf Coast and Florida. Above normal precipitation 
is also indicated over western Alaska. For the remaining areas of the 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 
 
ENSO-neutral conditions returned during the past month, and SSTs in the Niño3.4 
region recently dropped to 0.0 degrees Celsius. SSTs in Niño4 remain mildly 
above normal at 0.6 degrees Celsius, while Niño3 has dropped to -0.2 degrees 
Celsius and Niño1+2 to -0.6 degrees Celsius. More generally, in the last four 
weeks, equatorial SSTs were above average in the west-central Pacific Ocean and 
near-to-below-average SSTs were evident in the east-central and eastern Pacific 
Ocean. Collectively, the coupled ocean-atmosphere system reflected ENSO-neutral 
conditions, and there has been a slight slowdown in the rate of cooling since 
last month. 
 
Starting in November 2023, positive subsurface temperature anomalies weakened 
to near zero. From late January to mid-April 2024, negative temperature 
anomalies emerged at the surface and strengthened. Over the last month, 
negative anomalies have weakened slightly, but dominate the eastern half of the 
equatorial Pacific Ocean. 
 
The Madden Julian Oscillation (MJO) recently weakened and there was little 
activity during the first half of June, and dynamical model forecasts of the 
Realtime Multivariate MJO index through the end of June are generally 
incoherent. As La Niña is favored to develop during JAS 2024 and persist 
through winter 2025, La Niña is considered the dominant extratropical influence 
on the forecast. 
 
Outside of the equatorial Pacific, SST anomalies are below normal near the 
Alaska coast, particularly off the west coast of the state. Weak, below normal 
SST anomalies are also observed along the west coast of the CONUS, though they 
are weak and spotty. Strong above normal SST anomalies are present in the Gulf 
of Mexico and up much of the East Coast of the CONUS. Soil moisture varies 
across much of the CONUS but is notably anomalously low over much of New Mexico 
and southwestern Texas. 
 
PROGNOSTIC DISCUSSION OF SST FORECASTS 
 
The CPC Niño3.4 SST consolidation forecast favors a transition to a La Niña 
state by JAS 2024. Below zero SST anomalies are forecast in the mean of most 
inputs to the consolidation through April-June 2025 (AMJ). Forecast plumes of 
the Niño3.4 index from the North American Multi-Model Ensemble (NMME) generally 
indicate below zero SST anomalies from July 2024 through January 2025, though 
some models and ensemble members indicate ENSO-neutral conditions - for 
example, the GFDL-SPEAR model has a number of ensemble members with anomalies 
that stay near or slightly above zero degrees Celsius. The CPC Probabilistic 
ENSO outlook favors ENSO-neutral in May-July 2024 (MJJ) and June-August 2024 
(JJA), with chances of La Niña developing in JAS (65% chance) and persisting 
through the Northern Hemisphere winter 2024-25. 
 
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS 
 
Dynamical model forecasts from the Copernicus (C3S) and NMME multi-model 
ensemble systems are used for the first three and six leads respectively, as 
well as individual model forecasts from the Climate Forecast System version 2 
(CFSv2) and European Centre for Medium Range Weather Forecasts (ECMWF) models 
as available. The objective, historical skill weighted consolidation that 
combines both dynamical and statistical forecast tools was also considered 
throughout all leads. The Calibration, Bridging and Merging (CBaM) tool 
anchored to the NMME forecasts and "bridged" to the Niño3.4 index is also 
utilized. 
 
La Niña impacts were considered given the forecasted event from JAS through 
roughly March-April-May (MAM) 2025 as appropriate for the region, variable, and 
season, and La Niña composites and correlations of temperature and 
precipitation with the Niño3.4 region were used to determine typical La Niña 
impacts. Statistical guidance such as the global SST based Constructed Analog 
(CA) and long term (decadal) temperature and precipitation trends  played a role 
in many of the outlook seasons, particularly beyond lead 6 when dynamical model 
guidance is unavailable. Coastal SSTs and soil moisture anomalies are 
considered at early leads. 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 is used 
throughout the outlooks from JAS 2024 to JAS 2025. 
 
 
PROGNOSTIC DISCUSSION OF OUTLOOKS - JAS 2024 TO JAS 2025 
 
TEMPERATURE 
 
 The JAS 2024 Temperature Outlook favors above normal temperatures for much of 
the CONUS, with higher probabilities reaching 70 to 80% over parts of the Four 
Corners region where there was strong model agreement, the decadal temperature 
trend is above normal, and there are favored odds of below normal 
precipitation. Above normal temperature probabilities are also enhanced along 
the extreme Gulf Coast, reaching 60 to 70%, owing to strongly positive SST 
anomalies in the Gulf of Mexico and around Florida. Enhanced probabilities, 
reaching 50 to 60% are favored along the eastern seaboard into New England and 
parts of the eastern Great Lakes due to model agreement, warm coastal SSTs, and 
above normal decadal temperature trend over New England. Though still above 
normal, probabilities are relatively weaker over eastern parts of the Northern 
Plains stretching southward to the Southern plains where we might expect some 
minor modulation of temperatures given the forecasted La Niña, though not 
enough to tilt the odds toward below normal. EC is favored over the West Coast 
given cooler SST anomalies (leading to an enhanced seabreeze) and due to the 
potential for early impacts of La Niña over the Pacific Northwest as the JAS 
season progresses. SSTs are anomalously cold along the southern and western 
coast of Alaska leading to a slight tilt toward below normal temperatures over 
the southwestern part of the state, which is also coincident with expected 
early La Niña teleconnections. Probabilities transition to above normal toward 
the northeastern part of Alaska given forecasts from NMME and C3S. 
 
The next two seasons, August-October (ASO) 2024 and September-November (SON) 
2024 also depict favored probabilities of above normal temperatures across the 
majority of the CONUS, again driven by model agreement and strong decadal 
trends particularly over the western CONUS and New England. Areas of exception 
are the West Coast and Pacific Northwest in ASO and the Pacific Northwest in 
SON where EC is favored given expected impacts from La Niña and the cooler 
coastal SSTs. The temperature outlook for Alaska 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 . 
 
La Niña impacts are the key driver of the forecast during winter and early 
spring 2024-2025, and the forecasts generally depict below normal temperature 
probabilities over the Pacific Northwest and stretching into parts of the 
Central Plains from NDJ 2024-2025 through MAM 2025, with above normal 
temperatures over the southern tier of the CONUS. For longer leads beginning in 
AMJ 2025 through JAS 2025, the forecast is dominated by temperature trends , 
where above normal temperatures are favored across much of the CONUS excepting 
parts of the Northern Plains where trends  are weaker. 
 
PRECIPITATION 
 
The JAS 2024 Precipitation Outlook favors below normal precipitation over parts 
of the western and central CONUS. EC is indicated over the southern West Coast 
and parts of western Nevada, as these regions are climatologically drier, and 
over the Pacific Northwest where model forecasts are weak and inconsistent. 50 
to 60% chances of below normal precipitation are favored over eastern Arizona, 
western New Mexico, and parts of the Four Corners region where dynamical model 
agreement was strongest and in agreement with early impacts of La Niña for 
some regions. Given anomalously low soil moisture over parts of eastern New 
Mexico and western Texas, 40 to 50% probabilities of below normal precipitation 
are indicated. Enhanced probabilities for above normal precipitation are 
depicted over the Southeast and along the Eastern Seaboard to New England, with 
the highest probabilities reaching 50 to 60% over the coastal Gulf States, 
Florida, and coastal South Carolina owing to a forecasted above normal 
hurricane season and given early impacts of La Niña. Probabilities remain 
enhanced, reaching 40 to 50% above normal, along the East Coast into coastal 
New England given the chance of storminess continuing along the coast. This 
pattern is generally favored for the CONUS into ASO 2024. Above normal 
precipitation is forecast for much of Alaska in JAS 2024 based mainly on NMME 
and C3S, excluding the northeastern part of the state where model signals  were 
weak. 
 
Beginning in late fall 2024 into winter and early spring 2025, a canonical La 
Niña precipitation pattern is favored over the CONUS. Above normal 
precipitation is indicated over the north coast of Alaska and the Pacific 
Northwest stretching into the Central Plains and shifting eastward to the Great 
Lakes as the forecast progresses through February-April (FMA) 2025. Below 
normal precipitation is favored across the southern tier of the CONUS and south 
coast of Alaska through roughly February-April (FMA) 2024. The remaining leads, 
MAM 2025 through JAS 2025 are based mainly on decadal trends  which favor drier 
conditions over the Southwest (MAM 2025), and over the Northern and Central 
Plains from AMJ 2025 through JAS 2025. A small region of above normal 
precipitation is favored over southern New England and the Mid-Atlantic in JAS 
2025 given decadal trends . Above normal precipitation is favored for parts of 
the North Slope of Alaska, due to positive decadal trends  in precipitation, 
shifting to the south coast by JAS 2025. 
 
FORECASTER: Johnna Infanti 
 
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 18 2024 
 
 
1991-2020 base period means were implemented effective with the May 20, 2021 
forecast release. 
$$