Prognostic Discussion for Long-Lead Seasonal Outlooks 
NWS Climate Prediction Center College Park MD 
830 AM EDT Thu Apr 18 2024 

SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS 

During mid-April 2024, an El Niño Advisory remains in effect but the oceanic  
temperature anomalies associated with El Niño are rapidly fading. There is an  
85% chance that ENSO neutral will be in place by the end of the April-May-June  
(AMJ) season. There is a 60% chance of additional transitioning of the ENSO  
phase from ENSO Neutral to La Niña by summer (June-July-August, JJA), with La  
Niña conditions favored to strengthen and continue through boreal autumn and  
winter. Therefore, a La Niña Watch has also been issued. 
The May-June-July (MJJ) 2024 temperature outlook favors above-normal seasonal  
mean temperatures for central and eastern Alaska, the far West excluding  
southwestern California, and most of the remainder of the Contiguous U.S.  
(CONUS) with the exception of the north-central states.  Maximum probabilities  
(>50%) favoring above-normal temperatures are indicated over eastern Alaska,  
parts of the Northwest, the eastern Great Lakes and Northeast, and over New  
Mexico, southwestern Texas, and southern Florida. For southwestern California, 
 near-normal seasonal mean temperatures are favored. For remaining areas of the  
CONUS and Alaska, Equal Chances (EC) of below, near, and above-normal seasonal  
mean temperatures are favored. No areas of favored below-normal temperatures  
are forecast for the MJJ season. 



The MJJ 2024 precipitation outlook favors above-normal seasonal total  
precipitation amounts for approximately the western half of Alaska, and from  
the southeastern quarter of the CONUS northeastward across the Mid-Atlantic  
region, southeastern New York state, and southern New England. Below-normal  
precipitation is favored for parts of the northwestern CONUS, and from eastern  
sections of Utah and Arizona eastward across Colorado, New Mexico, and much of  
West Texas. For the remaining areas of the CONUS and Alaska, where seasonal  
total precipitation amounts are favored 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 

El Niño is fading rapidly as equatorial Pacific sea surface temperatures (SSTs)  
continue to cool, associated with upwelling from an oceanic Kelvin wave. The  
most recent weekly value of the Niño3.4 SST index is a surprisingly high +0.9  
degrees C, which is a bit misleading given the very shallow layer of subsurface  
warmth underlying this area.  Relatively cold water (departures ranging from  
-0.5 degrees C to at least -6 degrees C) is in place from the surface between  
120W and 100W longitude, extending westward and deepening across most of the  
equatorial Pacific, reaching a depth of 150 to 300 meters at 150E longitude  
(the approximate longitude of the Solomon Islands and Coral Sea). Tropical  
convection is now slightly suppressed across the vicinity of the Date Line and  
the equator, and close to average over Indonesia. These anomalies, in addition  
to the return of low-level easterly wind anomalies to the west-central Pacific  
Ocean are indicative of the underlying transition from El Niño to ENSO-neutral. 



As of mid-April 2024, above-normal soil moisture is present in many areas of  
the CONUS – including many areas west of the Continental Divide, the  
north-central Plains, from the southern Great Lakes eastward across the  
Northeast and Mid-Atlantic region, and from the vicinity of the Texas-Oklahoma  
Panhandles east-southeastward across the Arklatex region and Gulf Coast states.  
Drier than normal soils are evident over northern North Dakota, northwestern  
Minnesota, in the vicinity of the Washington Cascades rain shadow and Northern 
 Rockies, and across much of New Mexico and southwestern Texas. Drier than 
 normal soils are also indicated in a wishbone-shaped pattern that extends from 
 the Upper Great Lakes region southwestward across Iowa, southeastern Nebraska, 
 and Kansas, which then largely reverses direction and continues eastward across 
 the Middle Mississippi, southern Ohio, and Tennessee Valleys. Soil moisture 
 anomalies are an important consideration for the Seasonal Outlooks through the 
 warm half of the year. 

PROGNOSTIC DISCUSSION OF SST FORECASTS 

Forecasts of the Niño 3.4 SST index from the North American Multi-Model 
 Ensemble (NMME) are generally in good agreement for a nominal La Niña (Oceanic 
 Niño Index or ONI <=-0.5 degrees C) by June. Most participant model predictions 
 are slightly cooler than the NMME average, with the exceptions of the GFDL 
 SPEAR and Canadian CanCM4i models. The former does not reach the La Niña 
 threshold until mid-August.  The International Multi-Model Ensemble (IMME, C3S, 
 or Copernicus) average reaches the La Niña threshold by August. Three of the 
 participant models (German DWD, ECMWF, and METEO-France) stay within the 
 confines of ENSO-neutral limits at least into September, while the UKMO and 
 CMCC are considerably cooler and reach marginal La Niña conditions by late May 
 into June. The CFS is the coldest of solutions, exceeding the minimal La Niña 
 threshold even before MJJ, and predicts a strong La Niña (ONI>=-1.5 degrees C) 
 by July-August-September (JAS) 2024. CPC’s SST Consolidation for the Niño 3.4 
 region passes into La Niña territory by JJA, peaks during the overlapping 
 seasons of September-October-November (SON) and October-November-December (OND) 
 at -1.4 degrees C (just short of a strong cold event), and then retreats into 
 Neutral territory by March-April-May (MAM) 2025. As noted earlier, CPC’s ENSO 
 Team predicts the transition from El Niño to ENSO-neutral should be completed 
 within the AMJ season (85% chance), with the odds of La Niña developing by JJA 
 (60% chance). Historically, La Niña tends to follow strong El Niño events, 
 adding confidence to the forecast. 

PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS 

Though some remaining El Niño atmospheric response could extend into the very 
 early stages of the MJJ Outlook, it is unlikely to make a significant 
 difference for the season as a whole. Dynamical model forecasts from the NMME 
 and C3S multi-model ensemble systems are utilized, as is the Calibration, 
 Bridging and Merging (CBaM) tool anchored to the NMME forecasts and “bridged” 
 with the Niño 3.4 index – primarily for temperature outlooks. The Constructed 
 Analog (CA) statistical tools based on SST and soil moisture, along with the 
 ENSO-OCN forecast tool that targets impacts from ENSO as predicted by the CPC 
 consolidation Niño 3.4 SST forecast and long-term trends, played a large role 
 in many of the outlooks. La Niña impacts are considered in the outlooks from 
 JJA 2024 through February-March-April (FMA) 2025. 
 
PROGNOSTIC DISCUSSION OF OUTLOOKS - MJJ 2024 TO MJJ 2025 TEMPERATURE 

The MJJ 2024 seasonal temperature outlook favors above-normal seasonal mean 
 temperatures for central and eastern Alaska, the far west excluding 
 southwestern California, and most of the remainder of the CONUS with the 
 exception of the north-central states.  Maximum probabilities (>50%) favoring 
 above-normal temperatures are indicated over far eastern Alaska, parts of the 
 Northwest, the eastern Great Lakes and Northeast, and over New Mexico, 
 southwestern Texas, and southern Florida. For southwestern California, 
 near-normal seasonal mean temperatures are favored.  The reduced coverage (from 
 last month’s Lead 2 MJJ outlook) of 50%+ probability favoring above-normal 
 temperatures over the Northwest is related to anticipated diminished influences 
 from lagged El Niño impacts, slightly cooler effects of wet soils (through 
 evaporation) over southern Oregon and southern Idaho, and trends.  In 
 southwestern California, favored near-normal temperatures is thought to be the 
 best compromise given NMME and C3S SST regional forecasts of near to 
 below-normal in this region extending southward along Baja, during the MJJ 
 season.  Near the coast of Southern California, this may be associated with 
 prolonged or more frequent marine layer intrusions, a well-known climatological 
 feature in this region. Across the central portion of the CONUS, anomalous 
 warmth is favored to replace the southern part of the EC region (from last 
 month’s MJJ Outlook), and is favored by statistical and dynamical model 
 guidance. The recent very heavy rainfall (8-10+ inches) and severe weather over 
 the Ark-La-Tex region and Lower Mississippi Valley is the reason behind the 
 slightly lower odds favoring above-normal temperatures in that area. Model 
 guidance and trends (as shown by the OCN tool) favor relative maxima in 
 probabilities for above-normal temperatures across New Mexico and southwestern 
 Texas, and from the eastern Great Lakes region to the Northeast and 
 Mid-Atlantic coasts. Most tools support above-normal temperatures across the 
 Southeast. To the north, the outlook for Alaska is based on a subjective 
 consensus of model guidance, temperature trends, and anticipated residual 
 influences from sea ice. 

 

For JJA and JAS 2024, the favored above-normal temperatures in central and  
eastern Alaska from the preceding MJJ outlook are expected to decrease in 
 coverage and gradually become concentrated over the far northern part of the 
 state. In JJA, favored below-normal temperatures are depicted over the 
 southwest portion of the Mainland and the adjacent Alaska Peninsula, spreading 
 eastward across the southern coast with time. This is partly due to the 
 anticipated emerging effects of La Niña, and supported by the ENSO-OCN tool and 
 the Statistical Consolidation (Stat-CON). For the CONUS, probabilities favoring 
 above-normal temperatures exceed 50% for most of the interior West and 
 south-central states, warranted by the ENSO-OCN, Stat-CON, Dynamical 
 Consolidation (NMME-CON), and a skill-weighted mean of the two CON tools (the 
 Final CON). This is also consistent with most other tools, such as the CBaM 
 tool, the IMME, and longer-term trends. The favored area of EC in the vicinity 
 of the Dakotas in JJA gradually gives way to favored above-normal temperatures 
 in JAS 2024, consistent with emerging influences of La Niña. The three CON 
 tools and trends favor elevated probabilities for above-normal temperatures in 
 the vicinity of the Northeast CONUS. In August-September-October (ASO), the 
 probabilities favoring above-normal temperatures begin to decline over the 
 Pacific Northwest, in preparation for the typical La Niña impacts that set up 
 during boreal autumn and winter. 

 

During SON through November-December-January (NDJ) 2024, the temperature  
outlooks favor a canonical La Niña response, with above-normal temperatures in 
 the Northwest and north-central CONUS giving way to EC, and to below-normal  
temperatures across the Pacific Northwest by NDJ. Above-normal temperatures are  
depicted across much of the southern and eastern CONUS, also consistent with a  
cold event. During this period, SON through NDJ 2024, ENSO composites gradually  
begin to favor a replacement of the below-normal temperatures across southern  
Alaska to EC, and the expansion of favored anomalous warmth across northern and  
western Alaska. SON is the most likely season for high probabilities (>60%) for  
favored above-normal temperatures across the northwestern coast of Alaska due  
to the seasonally delayed onset of sea ice formation. From  
December-January-February (DJF) 2024-25 through MAM 2025, La Niña composites  
are primarily used in conjunction with model guidance. For the final two leads,  
AMJ and MJJ 2025, temperature trends are heavily utilized. For remaining areas  
of the CONUS and Alaska, EC favored.  

PRECIPITATION 

The MJJ 2024 seasonal precipitation outlook favors above-normal seasonal total  
precipitation amounts for approximately the western half of Alaska, and from  
the southeastern quarter of the CONUS northeastward across the Mid-Atlantic  
region, southeastern New York state, and southern New England.  These anomalies  
are generally consistent with NMME & C3S multi-model ensemble guidance, CFS,  
and trends. Below-normal precipitation is favored for parts of the northwestern  
CONUS, mostly from ENSO-OCN and the last vestiges of lagged El Niño influences.  
Anomalous dryness is favored from much of the Four Corners region to West  
Texas. This is consistent with the three CON tools, CFS, C3S, NMME, and to some  
extent, the SST Constructed Analog (SST-CA) statistical tool. There is also a  
significant negative correlation between this strong dry signal over the  
eastern Monsoon region and abundant snowpack over the Central Rockies (Colorado 
 and Utah). Historically, this correlation favors a slow start to, and potential  
underperformance of, the Southwest Monsoon. For the remaining areas of the  
CONUS and Alaska, where seasonal total precipitation amounts are favored to be  
similar to climatological probabilities, EC is forecast. 



From JJA and JAS 2024, widespread above-normal precipitation is favored in  
Alaska, consistent with NMME guidance. Afterwards, there is a slight tilt in  
the odds towards below-normal precipitation for Southeast Alaska for SON  
through NDJ 2024. From SON 2024 to MAM 2025, the main climate driver/forcing is  
the anticipated La Niña, which favors an enhanced storm track and above-normal  
precipitation amounts across the northwestern states, and also (starting with  
DJF 2024-25) over the Great Lakes and Ohio/Tennessee Valleys.  Enhanced dryness  
and below-normal precipitation amounts are favored across much of the southern  
CONUS and Eastern Seaboard. For the last two leads, April-May-June (AMJ) and  
MJJ 2025, the seasonal precipitation outlooks are largely based on trends. 

FORECASTER: Anthony Artusa 

The Climatic normals are based on conditions between 1991 and 2020, following  
the World Meteorological 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 Case 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.shtml 
 (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 May 16, 2024 


1991-2020 base period means were implemented effective with the May 20, 2021  
forecast release. 
$$