Prognostic Discussion for Monthly Outlook 
NWS Climate Prediction Center College Park MD 
830 AM EDT Thu Apr 17 2025 
 
 
30-DAY OUTLOOK DISCUSSION FOR MAY 2025 
 
The May 2025 outlooks are issued against the backdrop of transition from the 
cold phase to the neutral phase of the El Niño Southern Oscillation (ENSO). The 
latest Niño 3.4 weekly sea surface temperature (SST) departures stood at -0.1 
degrees Celsius which puts us firmly in ENSO-Neutral territory. ENSO-neutral 
conditions are expected to continue during the month of May. Meanwhile, the 
magnitude of the Real-time Multivariate (RMM) based Madden Julian Oscillation 
(MJO) index is weak. However, there is some evidence of a re-emergence of the 
MJO across the Western Pacific by late April. Uncertainty in this signal is 
high due to potential Kelvin Wave interference with this potential MJO 
re-emergence. Due to the current weakness and uncertainty in its evolution, the 
MJO did not play a major role in the May 2025 outlook. Farther to the north, 
across the extratropics of the Northern Hemisphere, the Arctic Oscillation 
(AO), the North Atlantic Oscillation (NAO), and the Pacific North America (PNA) 
index have all been positive for much of the past 10 days. However, all have 
trended less positive during the past few days with the AO and NAO both 
negative as of the most recent observations. Combined natural analog composites 
derived from the recent evolution of tropical and extratropical indices depict 
a 500-hPa flow pattern dominated by above normal heights across the Aleutians 
and southwestern Mainland Alaska as well as over the southwestern Contiguous 
United States (CONUS) for the month of May. Anomalous troughing is generally 
favored across the Great Lakes and Northeast as well as parts of Southeast 
Alaska. Meanwhile, trends  during the last 15 years favor above normal heights 
across most of the eastern CONUS, eastern Alaska, and the Aleutians with trends  
toward below normal heights across much of the southwestern CONUS and parts of 
southwestern Alaska. As the sun angle increases during the month of May, 
antecedent soil moisture conditions become more of a factor in the outlook. 
Currently, soil moisture deficits are observed across much of the southwestern 
and southeastern CONUS, much of the Plains, and much of the Mid-Atlantic and 
Northeast. Soil moisture surpluses are currently observed for much of the Ohio, 
Tennessee, and Lower Mississippi Valleys, parts of the Upper Great Lakes, and 
parts of northern California and Oregon. Sea surface temperatures (SSTs) are 
currently above normal adjacent to the South Coast of Alaska, much of the West 
and Gulf Coasts of the CONUS, and the southern half of the Eastern Seaboard. 
Below normal SSTs are observed near the Northeast/northern Mid Atlantic coasts 
and near extreme southern California. Natural analog composites, trends , and 
dynamical guidance from the Copernicus Climate Change Service (C3S), North 
American Multi-Model Ensemble (NMME), the Couple Forecast System Version 2 
(CFSv2), and the Forecast Consolidation Tool (CON) (which includes both 
dynamical model input and statistical guidance) form the basis of the May 
outlooks. The latest CPC Weeks 3-4 Outlooks and associated ensemble guidance 
from the European Centre for Medium Range Weather Forecasts (ECMWF), Global 
Ensemble Forecast System (GEFS), and the CFS also contributed. Antecedent 
conditions such as extratropical SSTs, sea ice extent, and soil moisture 
conditions were also considered where appropriate. 
 
Above normal temperatures are favored for most of the western CONUS, consistent 
with anomalous ridging. The strongest probabilities (greater than 50 percent) 
of above normal temperatures are indicated from western portions of the Rio 
Grande Valley northward to the Four Corners region, where dynamical and 
statistical guidance show the strongest agreement. A tilt toward above normal 
temperatures also extends northeastward to parts of the Northern and Central 
Plains consistent with observed below normal soil moisture. Probabilities of 
warmer than normal conditions are tempered across parts of the northwestern 
CONUS, due to cold signals  depicted by ENSO-based natural analogs . Farther to 
the south and east, enhanced above normal temperature probabilities are 
indicated across the Southern Plains, Lower Mississippi Valley, and the 
Southeast, due to generally good agreement among dynamical and statistical 
model guidance. Probabilities of above normal temperatures exceed 40 percent 
for much of the Gulf Coast region and Southeast and exceed 50 percent over 
southern Florida, where SSTs in adjacent waters are warmer than normal. Equal 
chances (EC) of above, near, and below normal temperatures are indicated for 
the Northeast, Great Lakes, northern Mid Atlantic, as well as the Upper and 
Middle Mississippi Valley, the Ohio Valley, and the Tennessee Valley. Dynamical 
models generally depict warm or weak signals  in these areas while statistical 
guidance generally favors cooler outcomes. Above normal soil moisture across 
the Ohio, Tennessee, and parts of the Middle and Lower Mississippi valleys 
reduce chances of above normal temperatures across these areas. Similarly, 
below normal SSTs adjacent to the northern Mid-Atlantic and Northeast increase 
chances of back-door cold fronts common for this time of year, resulting in a 
reduction of above normal temperature probabilities relative to what is 
depicted by dynamical model guidance such as the NMME and C3S and recent 
trends. Above normal temperatures are favored for southwestern Alaska and the 
North Slope, consistent with the consensus of dynamical and statistical model 
guidance. Above normal SSTs and below normal Arctic sea ice also contributed to 
increased above normal temperature probabilities for these areas. However, EC 
is indicated for much of the remainder of Alaska due to conflicting signals  
among dynamical and statistical model guidance and as well as the presence of 
lingering sea ice adjacent to parts of western mainland Alaska. 
 
Above normal precipitation is favored across the northern Mid-Atlantic region 
and southern portions of the Northeast, extending southwestward across the Ohio 
Valley and parts of the Lower and Middle Mississippi Valleys. The wetness 
across parts of the Mid-Atlantic and Northeast aligns with CPC’s Weeks 3-4 
outlooks, the final consolidation (for the Mid-Atlantic), and the potential for 
anomalous troughing depicted by the natural analogs . The southwestern extension 
of the area of enhanced above normal precipitation probabilities across much of 
the Ohio and Middle and Lower Mississippi Valleys is driven largely by 
abnormally high soil moisture content. Conversely, below normal precipitation 
is likely across much of the West due to good agreement among dynamical model 
guidance, natural analogs , and CPC’s weeks 3-4 guidance. An tilt toward below 
normal precipitation extends to much of the Northern Plains consistent with 
currently observed below normal soil moisture. Similarly, a slight tilt toward 
below normal precipitation is indicated for much of Florida and adjacent areas 
of the Southeast consistent with below normal soil moisture and CPC’s weeks 3-4 
outlooks. Farther to the north, below normal precipitation is favored for 
southwestern Alaska consistent with CON guidance and increased ridging 
suggested by the natural analogs . A weak tilt toward above normal precipitation 
is indicated for eastern and northern Alaska due to monthly guidance from the 
CON, C3S, and recent trends . 
 
FORECASTER: Scott Handel 
 
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 climate 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. 
 
An updated monthly outlook... for May will be issued on Wed April 30 2025 
 
These outlooks are based on departures from the 1991-2020 base period. 
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