Prognostic Discussion for Long-Lead Seasonal Outlooks 
NWS Climate Prediction Center College Park MD 
830 AM EDT Thu May 18 2023 
 
SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS 
 
El Niño Southern Oscillation (ENSO) neutral conditions are currently observed, 
and equatorial sea surface temperatures are near-to-above average across most 
of the Pacific Ocean. An El Niño watch is in effect as a transition from 
ENSO-neutral to El Niño is favored during May-July 2023, with chances of El 
Niño increasing to greater than 90% in winter 2023-2024. 
 
The June-July-August (JJA) 2023 temperature outlook favors above normal 
temperatures over the western contiguous United States (CONUS), the southwest, 
southeast, and along the eastern seaboard to New England. A tilt toward warmer 
than normal temperatures is also favored over most of Alaska. The largest 
probabilities of above normal temperatures (60 to 70 percent) are forecast over 
the Southwest, and probabilities reach 50 to 60 percent along the coast from 
Texas to New England. The JJA precipitation outlook favors below normal 
precipitation probabilities over the Pacific Northwest, Southwest, and south 
coast of Alaska. Above normal precipitation probabilities are more likely for 
the eastern CONUS, including the Southeast, Mid-Atlantic, Lower and Middle 
Mississippi Valley. The North Slope of Alaska also tilts weakly above normal. 
Equal chances (EC) are forecast for areas where probabilities for each category 
of seasonal mean temperatures and seasonal accumulated precipitation amounts 
are expected to be similar to climatological probabilities. 
 
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 
 
Equatorial SSTs are near-to-above average across most of the Pacific Ocean and 
atmospheric conditions reflect ENSO-neutral conditions. Since early April 2023, 
near-to-above average SSTs have persisted across most of the tropical Pacific 
Ocean, and eastern Pacific positive SSTs have expanded westward to the 
east-central Pacific ocean. Weekly SST departures remain largest in the NINO1+2 
region reaching 2.4 degrees Celsius above normal, while the NINO3.4 region has 
reached 0.5 degrees Celsius above normal. Subsurface temperature anomalies 
became positive in February and have increased through mid-April, and positive 
subsurface temperature anomalies now dominate the equatorial Pacific Ocean. 
During the last 30 days, weak suppressed convection was observed near the 
equator over Indonesia, and low-level winds were near average across most of 
the equatorial Pacific Ocean, reflecting ENSO-neutral conditions. 
 
The Madden Julian Oscillation (MJO) has remained active, and the enhanced phase 
propagated eastward from the Maritime Continent into the western Pacific during 
the past week. The Realtime Multivariate MJO (RMM) index for early April 2023 
through mid-May 2023 indicates that the MJO signal completed another global 
circumnavigation, however the MJO recently decreased in amplitude over the 
western Pacific due to destructively interfering Kelvin and Rossby Wave 
activity. RMM forecasts show the MJO regaining amplitude over the western 
Pacific at a slow phase speed in the upcoming week and propagating slowly 
across the western Pacific through late May. In RMM forecasts, some ensemble 
members from the Global Ensemble Forecast System version 12 (GEFSv12) and the 
European Centre for Medium-Range Weather Forecast (ECMWF) model forecast 
continuation of the MJO into the end of May, but the ensemble mean ECMWF 
indicates that MJO activity may wane. 
 
PROGNOSTIC DISCUSSION OF SST FORECASTS 
 
The latest Probabilistic ENSO Outlook issued in May 2023 favors a transition 
from ENSO-neutral to El Niño during May-July (MJJ) 2023, with chances of El 
Niño increasing to greater than 90% into winter 2023-24, and an El Niño Watch 
is in effect. The most recent plume from the International Research Institute 
(IRI) also indicates likely formation of El Niño in the May to July seasons and 
persistence into the winter. At least a weak El Niño is likely given high 
levels of above-average oceanic heat content, but the range of possibilities 
include an 80 percent chance of at least a moderate El Niño and a 55 percent 
chance of a strong El Niño by the end of the year. Dynamical model forecasts 
from the North American Multi Model Ensemble (NMME) and the Climate Forecast 
System model version 2 (CFSv2) favor a moderate to strong El Niño through 
November-January (NDJ) 2024 while they are available, and forecasts become more 
uncertain in spring and summer 2024 based on statistical models. 
 
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS 
 
Dynamical model forecasts from the NMME, CFSv2, and Copernicus (C3S) 
multi-model ensemble systems are used for the first six leads when they are 
available as was the objective, historical skill weighted consolidation, that 
combines both dynamical and statistical forecast tools. The Calibration, 
Bridging and Merging (CBaM) tool anchored to the NMME forecasts and "bridged" 
to the Niño3.4 index is also significantly utilized. El Niño impacts were 
considered given the elevated probability of transition to El Niño during MJJ 
2023, and El Niño composites and correlation/regression of temperature and 
precipitation with the NINO3.4 region were used to determine typical El Niño 
impacts. Statistical guidance such as the global SST based Constructed Analog 
(CA) and long term temperature and precipitation trends  played a role in many 
of the outlook seasons, particularly beyond lead 6 when dynamical model 
guidance is unavailable. Antecedent soil moisture conditions and coastal SSTs 
are considered at early leads. 
 
PROGNOSTIC DISCUSSION OF OUTLOOKS - JJA 2023 TO JJA 2024 
 
TEMPERATURE 
 
The JJA 2023 temperature outlook favors above normal temperatures over the 
western CONUS, the Southwest, the Gulf States, along the eastern seaboard, and 
for much of the state of Alaska. The highest probabilities of above normal 
temperatures (60 to 70 percent) are over parts of the Southwest, Southern 
Rockies, and western Southern Plains where NMME and C3S show consistent strong 
probabilities of above normal temperatures, soil moisture is anomalously dry, 
decadal temperature trend is above normal, and where precipitation is forecast 
to tilt toward below normal for this season. 50 to 60 percent probabilities are 
indicated from the Southwest along the coast to New England where there was 
strong model agreement as well as support from above normal decadal temperature 
trends and above normal coastal SSTs. A weak tilt toward above normal 
temperatures (33 to 40 percent) is forecast over California owing to weaker 
temperature signals  in NMME and C3S, likely related to recent coastal SST 
anomalies that leaned below normal and recently transitioned to neutral. A weak 
tilt toward above normal temperatures is also indicated over western Oregon and 
Washington given a slight weakness in dynamical models  as well as mixed month 
to month temperature teleconnection to El Niño as it evolves through JJA. EC of 
above, near, and below normal temperatures are depicted over parts of the 
Northern Plains to the Great Lakes and parts of the Ohio River Valley were 
tools where weak or had inconsistent signals , and given currently neutral Great 
Lakes temperatures. Over Alaska, NMME, C3S, CFSv2, and CBaM all favor a tilt 
toward above normal temperatures over the southern half of the state, 
consistent with expected ENSO teleconnection in JJA, while statistical tools 
indicate EC over northern parts of the state and a spatially small, very weak 
tilt toward below normal decadal trend. Anomalously cold SSTs along the 
southwestern coast of Alaska led to a moderation of probabilities over the 
southwest part of the state. 
 
For the remainder of the summer and into early fall (July-September, JAS 
through August-October, ASO), 50 to 60 percent probabilities of above normal 
temperatures are maintained over the western CONUS and stretching along the 
eastern seaboard where agreement remains among dynamical and statistical tools, 
and due to strong probabilities in the objective skill-based consolidation. 
Probabilities over Alaska also remain above normal with the largest 
probabilities over the southern half of the state where there is dynamical and 
statistical model agreement. Compared to last month’s JAS and ASO forecasts, 
probabilities are slightly increased over the Ohio and Tennessee Valley regions 
and along the coast given strong probabilities in CBaM, NMME, and CFSv2 and 
where the objective skill based consolidation had higher probabilities. EC is 
maintained over the central CONUS where signals  were weak, though the eastern 
Great Lakes tilt above normal consistent with dynamical models . 
 
Confidence decreases in September-November (SON) 2023 and following seasons as 
lead time increases and dynamical models  become more uncertain, however, El 
Niño is expected to become more dominant in the forecast(s), and the pattern 
begins to reflect El Niño conditions during fall and winter seasons. Above 
normal temperatures are favored over the western and eastern CONUS, with 
highest probabilities reaching 50 to 60 percent over New England where decadal 
trends are strong. EC is indicated over parts of the central CONUS in SON and 
October-December (OND) given lack of consistent signal in tools. By fall and 
winter 2023-2024 (November through January, NDJ and December through February, 
DJF) we expect to begin seeing a canonical El Niño pattern of increased 
temperatures over the Northern Tier and a reduction of probabilities over the 
southern CONUS. Warmer than normal temperatures are generally favored over 
Alaska in the fall and winter months. Forecasts for spring and summer 2024 are 
more reliant on decadal trends  given the comparatively uncertain forecast of El 
Niño and lack of dynamical model data at longer leads, though probabilities are 
higher where decadal trends  and constructed analogues based on SSTs agree. 
February through April (FMA) 2024 has elevated probabilities of above normal 
temperatures over Alaska and the east coast, with probabilities over CONUS 
expanding westward in April through June (AMJ) and JJA 2024. 
 
PRECIPITATION 
 
The JJA 2023 precipitation outlook depicts below normal precipitation 
probabilities over the Pacific Northwest and parts of the Northern Rockies, the 
Southwest, and south coast of Alaska. The tilt toward below normal 
precipitation over the Pacific Northwest and south coast of Alaska is 
consistent with expected El Niño teleconnections as well as below normal 
decadal trends . NMME and C3S are in good agreement on below normal 
precipitation over the southwest and wet soil moisture over the Four Corners 
region may provide a sluggish start to the Monsoon this summer. Above normal 
precipitation probabilities are indicated over parts of the Middle and Lower 
Mississippi Valleys, the Ohio and Tennessee Valleys, the Southeast, and 
mid-Atlantic. Parts of the Central Plains tend to be anti-correlated with the 
monsoon region, and as such a weak tilt toward above normal precipitation is 
indicated. The remainder of the above normal region is due to enhanced 
probabilities in C3S and above normal decadal trends  with the highest 
probabilities aligned with where decadal precipitation trends  are strongest as 
well as recent high rainfall amounts. Though above normal precipitation 
probability is favored over the northern part of Alaska owing to weak decadal 
trends and above normal probabilities in CFSv2, probabilities are weak and EC 
is indicated for the central parts of Alaska given inconsistent signals  and 
significant changes from last month's forecast to this month’s. The dry signal 
over the Southwest is maintained through JAS 2023 as dynamical models  agree on 
below normal probabilities. The above normal precipitation over the eastern 
CONUS shifts westward in JAS 2023 owing to a reduction of probabilities over 
the southeast in the forecast consolidation. Above normal precipitation is 
maintained over Northern Alaska through JAS and into winter 2023 as dynamical 
models generally forecast above normal precipitation. Over the Pacific 
Northwest, a weak tilt toward below normal precipitation is favored through 
FMA2024 consistent with decadal trends  and constructed analogues based on SSTs. 
Above normal precipitation is favored for the Southeast and Gulf States owing 
to canonical El Niño teleconnection during the winter months. Below normal 
precipitation is depicted over the north Central Plains and Great Lakes during 
the winter, also consistent with El Niño. Decadal trends  become the dominant 
player in spring and summer 2024, with below normal trends  over the Pacific 
Northwest and above normal trends  over the Mid-Atlantic. Confidence decreases 
over Alaska in spring and summer 2024, with only a weak tilt toward above 
normal rainfall in March through May (MAM) 2024 over the northwest consistent 
with above normal precipitation trend, and EC indicated for the remaining leads 
given lack of clear signal. 
 
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 Jun 15 2023 
 
 
1991-2020 base period means were implemented effective with the May 20, 2021 
forecast release. 
$$