Prognostic Discussion for Long-Lead Seasonal Outlooks 
NWS Climate Prediction Center College Park MD 
830 AM EDT Thu Jul 18 2024 
 
SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS 
 
Currently, El Niño Southern Oscillation (ENSO) conditions are neutral with 
above average sea surface temperatures (SSTs) in the west-central Pacific 
Ocean, near average SSTs in the east-central Pacific Ocean, and below average 
SSTs in the far eastern Pacific Ocean. A La Niña watch is currently in effect 
and is favored to develop during August-September-October (ASO; 70% chance) and 
persist into the Northern Hemisphere winter 2024-25 (79% chance) during 
November-December-January (NDJ). As summer wanes and winter approaches, the 
overall temperature and precipitation patterns across the contiguous U.S. 
(CONUS) and Alaska are expected to transition to those associated with typical 
La Niña impacts. For the remainder of summer and early fall 2024 and again late 
spring and summer 2025, the overall outlooks resemble long-term decadal trends . 
 
The ASO 2024 Temperature Outlook favors above normal temperatures for much of 
the contiguous United States (CONUS), with the strongest probabilities reaching 
60 to 70% over parts of the Interior West and New England. Above normal 
temperature probabilities of 50 to 60% are forecast over the Gulf and Southeast 
Coasts, including Florida. In contrast, equal-chances (EC) of above-, near-, or 
below-normal temperatures are favored over the West Coast of CONUS and portions 
of the Northern Plains. 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 ASO 2024, except 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%) centered over Florida. Above normal precipitation is also indicated over 
western Alaska. For the remaining areas of CONUS, 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 are currently present in the equatorial tropical 
Pacific. Observed SST anomalies are -0.2 degrees Celsius in Niño1+2, -0.1 
degrees Celsius in Niño3, 0.7 degrees Celsius in Niño4, and 0.3 degrees Celsius 
in Niño3.4. In general, equatorial SST anomalies are above normal in the 
western Pacific and below normal in the eastern Pacific. With respect to 
atmospheric coupling, low-level wind anomalies are easterly over the western 
equatorial Pacific while upper-level wind anomalies are westerly over the 
eastern equatorial Pacific. Near to slightly above normal convection is 
observed over the western Pacific, as indicated by weakly negative outgoing 
longwave radiation (OLR) anomalies in that region. Overall, the current 
ocean-atmosphere coupling is indicative of ENSO-neutral conditions. 
 
Equatorial upper-ocean heat anomalies in the eastern Pacific turned negative in 
January 2024 and have persisted, strengthening and emerging at the surface from 
late winter into spring. Interestingly, the subsurface negative anomalies 
became less negative during late spring and early summer, currently 
approximately -0.5 degrees Celsius. Despite the weakening, the negative 
anomalies continue to prevail over the eastern half of the equatorial Pacific. 
 
The Madden Julian Oscillation (MJO) is currently weak, with little indication 
of eastward propagation in fields such as velocity potential and OLR. A robust 
stationary Wave-1 structure dominates, whose placement has produced upper level 
convergence over the Western Hemisphere. This convergence has acted to suppress 
tropical cyclone activity despite very warm SST anomalies in the Atlantic 
basin.  Dynamical model guidance of the MJO is mixed, with only the ECMWF 
hinting at a possible eastward propagation over the coming weeks. Should such a 
propagation occur, upper-level conditions will become more favorable for 
tropical cyclone formation that could impact CONUS. 
 
In the extratropics, coastal SST anomalies are below normal along the western 
coast of Alaska, with near normal anomalies along Alaska’s southern coast. Near 
normal SST anomalies are also observed along the West Coast of CONUS. Along the 
Gulf Coast and East Coast, SST anomalies are above normal. Current soil 
moisture anomalies are positive in the Upper Mississippi River Valley and 
eastern portions of the Northern Plains. They are also positive following the 
track of the remnants of Hurricane Beryl, particularly in eastern Texas. Large 
negative soil moisture anomalies are evident in the southern and central 
Appalachians. They are also negative in the Northern Rockies and Intermountain 
West. 
 
Surface temperatures thus far in July have been characterized by above normal 
temperatures in western and eastern CONUS, with pockets of near to below normal 
temperatures in the Central Plains due to transient cold fronts that have 
advected in cooler air. This overall pattern looks likely to continue through 
the end of July. Interestingly this pattern is reminiscent of the overall 
long-term warming trend during summer, which is weakest in the north-central 
part of CONUS. Precipitation in CONUS has been broadly below normal with a 
swath of above normal precipitation stretching from the Texas Gulf Coast to 
Maine due to Hurricane Beryl. An additional area of above normal precipitation 
has been observed in the southern Mid-Atlantic region. Temperatures in Alaska 
have been much below normal this July due to above normal precipitation caused 
by troughing and westerly flow into the state. 
 
PROGNOSTIC DISCUSSION OF SST FORECASTS 
 
The Nino3.4 SST consolidation forecast produced by CPC favors a transition to a 
La Niña state by ASO 2024 with anomalies less than -0.5 degrees Celsius 
persisting through February-March-April (FMA) 2025. While forecasted anomalies 
rebound in the following seasons they are still forecast to remain bounded 
between -0.5 and 0 degree Celsius through ASO 2025. Consistent with this 
forecast, the current ENSO Alert System Status is broadcasting a La Niña Watch 
for the winter of 2024-2025 with the CPC Probabilistic ENSO outlook favoring a 
70% chance of La Niña emerging by ASO 2024 and a 79% chance of La Niña during 
November-December-January (NDJ). With respect to coastal SST anomalies, near to 
below normal values are forecast by dynamical model guidance to more firmly 
establish through winter along the southern coast of Alaska and West Coast, 
consistent with typical upwelling observed during La Niña. 
 
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS 
 
A suite of multiple statistical and dynamical forecast tools is used to produce 
the temperature and precipitation outlooks for ASO 2024 to ASO 2025. 
 
Dynamical model forecasts from the Copernicus (C3S) and North American 
Multi-Model Ensemble (NMME) 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. In addition to the dynamical model guidance, coastal SSTs and 
soil moisture anomalies are considered at early leads. 
 
Because La Niña is favored to develop by and persist through winter 2024-25, La 
Niña impacts are considered the dominant influence on the forecast from ASO 
2024 through March-April-May (MAM) 2025. These impacts differ by region, 
variable, and season. To determine these impacts, La Niña composites and 
correlations of temperature and precipitation with the Niño3.4 region were 
employed via statistical tools such as the SST-based Constructed Analog (CA). 
Long-term decadal temperature and precipitation trends  also played a role 
during many of the seasons, especially beyond lead 6 when dynamical model 
guidance is unavailable. 
Longer lead outlooks, beginning in April-May-June (AMJ) 2025 are based 
primarily on decadal temperature and precipitation trends . 
 
 
PROGNOSTIC DISCUSSION OF OUTLOOKS - ASO 2024 TO ASO 2025 
 
TEMPERATURE 
 
The ASO 2024 Temperature Outlook depicts elevated probabilities of above normal 
temperatures throughout much of CONUS. The highest probabilities reach 60-70% 
north of the Four Corners region and New England where model guidance was in 
good agreement and decadal temperature trends  are strongly positive. Equal 
Chances (EC) of above-, near-, or below-normal temperature are posted for the 
immediate West Coast where coastal SSTs are expected to be below normal, 
leading to a potential maritime cooling impact. EC and a slight tilt in the 
odds toward above normal temperatures are forecast in the more interior regions 
of the Pacific Northwest, as La Niña impacts are expected to emerge by late in 
the season. Farther east, in Northern Plains and portions of the Midwest and 
Upper Mississippi River Valley, a combination of pattern persistence, less 
positive decadal temperature trends , and high climatological variance, 
particularly in October, has led to regions of EC and reduced odds of above 
normal temperatures. Furthermore, several models, such as the CFS, also depict 
a weakness in the temperature field in this region. 50 to 60% probabilities of 
above normal temperatures are favored along the Gulf Coast, Florida, and the 
Southeast Coast due to elevated SSTs and model agreement. In Alaska, above 
normal temperatures are forecast along the eastern North Slope due to decadal 
trends of sea ice loss. Below normal temperatures are favored in southwestern 
Alaska and the Aleutians due to below normal SSTs currently observed along with 
support from the CFS and NMME. Overall confidence in the temperature outlook 
for ASO 2024 is medium. While August and September generally have low 
climatological variance, that is not the cas e in October, where anomalies in 
that month can both overwhelm the trend and the combined anomalies in the prior 
two months. Further uncertainty is introduced due to the potential impact of 
tropical cyclones, especially in October when they can potentially usher in 
much cooler air on their western flanks. 
 
The temperature outlooks for September-October-November (SON) 2024 and 
October-November-December (OND) 2024 generally depict a transition from the 
summertime state which is dominated by decadal temperature trends  toward one 
that is more typical of La Niña. The overall pattern is consistent with ASO 
2024, with the highest probabilities for above normal temperatures in the West 
and New England. However, progressing through these seasons, the areas of EC 
and lower probabilities of above normal temperatures generally expand in the 
Pacific Northwest, Northern Plains, and Midwest. In fact, a small tilt in the 
odds toward below normal temperatures is forecast for the extreme northwestern 
corner of Washington state in OND 2024. The temperature outlook in Alaska 
increases the odds of above normal temperatures across all of the North Slope 
and shifts the highest odds of below normal temperatures to the entire southern 
third of the state, consistent with a transition to La Niña. 
 
Winter and early spring 2024-2025 temperatures are expected to be driven by La 
Niña impacts. The forecasts generally tilt the probabilities toward below 
normal temperatures 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 CONUS. For longer leads beginning in AMJ 
2025 through ASO 2025, the outlook resembles decadal temperature trends , where 
above normal temperatures are favored across much of CONUS except parts of the 
Northern Plains where trends  are weaker and even negative during the spring 
months. For Alaska, the temperature outlook progressively favors above normal 
temperatures over below normal temperatures due to long-term trends  and the 
waning influence of La Nina into the summer months. 
 
PRECIPITATION 
 
The ASO 2024 Precipitation Outlook depicts elevated odds of below normal 
precipitation over much of the interior of the West, with the highest odds 
centered over Utah, Colorado, and Wyoming. Probabilities to the south of this 
region are relatively muted compared to the previous outlook due to positive 
precipitation anomalies that have occurred thus far this summer in portions of 
Arizona, New Mexico, and southern Colorado. Nonetheless, below normal 
precipitation is still largely supported by dynamical model guidance such as 
the NMME, C3S, and CFS along with the growing influence of La Niña and weaker 
than normal tropical cyclone activity in the eastern Pacific. A small area of 
above normal precipitation is favored in the northwestern corner of Washington 
state as La Niña begins to impact the region later in the season. Along the 
Gulf Coast and East Coast, above normal probabilities of precipitation are 
posted consistent with the 2024 Atlantic Hurricane Season Outlook for above 
normal tropical cyclone activity. The highest probabilities reach 50 to 60% 
over Florida. EC is depicted in the remainder of CONUS, due to model 
disagreement and no strong decadal trends . Above normal precipitation is 
slightly favored in western Alaska due to anticipated onshore flow, which is a 
persistence of the current pattern, and the ECMWF. Overall confidence in the 
precipitation outlook for ASO 2024 is low to medium. Uncertainty is introduced 
due to the potential impact of tropical cyclones and their eventual tracks. 
 
The precipitation outlook in ASO 2024 largely persists into SON 2024 before 
transitioning by winter toward the canonical La Niña precipitation pattern. 
This pattern features elevated odds of below normal precipitation along the 
southern tier of CONUS from southern California to the Southeast. Above normal 
precipitation is favored over the Pacific Northwest and Great Lakes. At longer 
leads, including spring and summer 2025, the La Niña pattern fades and is 
replaced by large swaths of EC for much of CONUS. Only the Mid-Atlantic and 
northern portions of the West have a small tilt in their odds toward above and 
below normal precipitation, respectively, due to decadal trends . Above normal 
precipitation is favored for parts of the North Slope of Alaska, also due to 
decadal trends , shifting to the southern coast by ASO 2025. 
 
FORECASTER: Cory Baggett 
 
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 Aug 15 2024 
 
 
1991-2020 base period means were implemented effective with the May 20, 2021 
forecast release. 
$$