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FXUS07 KWBC 301901
PMD30D
PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT WED APR 30 2025
30-DAY OUTLOOK DISCUSSION FOR MAY 2025
THE UPDATED OUTLOOK FOR MAY REPRESENTS A CHALLENGING FORECAST WITH MUCH LOWER
THAN NORMAL CONFIDENCE. ONE OF THE MAIN CULPRITS FOR THIS UNCERTAINTY IS THE
PROSPECT OF A CUT-OFF LOW ACROSS THE WEST DURING THE FIRST WEEK OF THE MONTH.
THIS FORECAST CUT-OFF LOW IS LIKELY TO LEAD TO A COOLER AND MORE UNSETTLED
PERIOD ACROSS MUCH OF THE WEST RELATIVE TO GUIDANCE AVAILABLE DURING THE
PREVIOUS MID-MONTH OUTLOOK. ADDITIONALLY, THIS CUT-OFF LOW COMBINED WITH A
STALLED FRONTAL BOUNDARY SUPPORTS A MUCH MORE ACTIVE PERIOD ACROSS THE SOUTHERN
PLAINS DURING THE FIRST HALF OF MAY. MOREOVER, THE MADDEN JULIEN OSCILLATION
(MJO) REMAINS WEAK AND IS FORECAST TO REMAIN SO INTO MUCH OF MAY, REDUCING THE
UTILITY OF THE MJO AS A RELIABLE FORECAST TOOL FOR THIS UPCOMING MONTH.
FINALLY, AS WE PROGRESS FURTHER INTO SPRING, FORECAST SIGNALS FROM THE EL NIñO
SOUTHERN OSCILLATION (ENSO) BECOME LESS RELIABLE IN MANY AREAS AND ENSO-NEUTRAL
CONDITIONS ARE FORECAST TO PREVAIL DURING THE MONTH. DUE TO THESE COMBINATION
OF FACTORS, THE MAIN DRIVERS FOR THE UPDATED MAY OUTLOOKS WERE WPC’S SHORT
RANGE OUTLOOKS, CPC’S 6-10 DAY, 8-14 DAY, AND WEEKS 3-4 OUTLOOKS AND DYNAMICAL
MODEL GUIDANCE FROM THE CFSV2, GEFS, AND ECMWF. ANTECEDENT CONDITIONS SUCH AS
SOIL MOISTURE ANOMALIES, EXTRATROPICAL SEA SURFACE TEMPERATURES IN NEARBY
WATERS, AND SEA ICE EXTENT WERE ALSO UTILIZED IN THE OUTLOOK WHERE APPROPRIATE.
THESE COMBINATIONS OF TOOLS SIGNAL A SIGNIFICANT CHANGE FROM THE MID-MONTH MAY
OUTLOOK IN MANY AREAS.
SIMILAR TO THE HALF MONTH OUTLOOK FOR MAY, ABOVE NORMAL TEMPERATURES REMAIN
FAVORED ACROSS THE MAJORITY OF THE CONTIGUOUS UNITED STATES (CONUS). HOWEVER,
PROBABILITIES OF ABOVE NORMAL TEMPERATURES ARE SIGNIFICANTLY REDUCED ACROSS
MUCH OF THE WEST DUE TO THE PREDICTED CUT-OFF LOW EARLY IN THE MONTH.
CONVERSELY, INCREASED CONFIDENCE IN ABOVE NORMAL TEMPERATURES IS INDICATED FOR
MUCH OF THE NORTH-CENTRAL AND NORTHEASTERN CONUS AS ANOMALOUS RIDGING IS
FAVORED ACROSS THESE AREAS FOR MUCH OF THE FIRST HALF OF THE MONTH AND ABOVE
NORMAL 500-HPA HEIGHTS CONTINUE TO BE FAVORED INTO THE WEEKS 3-4 PERIOD. A
REDUCTION IN ABOVE NORMAL TEMPERATURE PROBABILITIES IS NOTED FOR THE FLORIDA
PENINSULA IN RESPONSE TO A COOL SIGNAL REPRESENTED IN CPC’S 6-10 DAY AND 8-14
DAY OUTLOOKS. MOREOVER, PROBABILITIES OF ABOVE NORMAL TEMPERATURES WERE REDUCED
FOR MUCH OF THE SOUTHERN PLAINS AS A WET PATTERN IS LIKELY TO TAKE HOLD FOR
MUCH OF THE FIRST HALF OF THE MONTH. THE FORECAST FOR ENHANCED ABOVE NORMAL
TEMPERATURE PROBABILITIES FOR SOUTHWESTERN ALASKA IN THE HALF MONTH LEAD
REMAINS ON TRACK IN THE UPDATED MAY OUTLOOK. HOWEVER, EQUAL CHANCES NOW
REPLACES THE TILT TOWARD ABOVE NORMAL TEMPERATURES ACROSS THE NORTH SLOPE OF
ALASKA AS BOTH THE 6-10 DAY AND 8-14 DAY CPC OUTLOOKS TILT COLD ACROSS THIS
REGION.
THE CUT-OFF LOW EXPECTED OVER THE WEST EARLY IN MAY SIGNIFICANTLY ALTERS THE
PRECIPITATION OUTLOOK ACROSS MANY AREAS. PRECIPITATION AMOUNTS FROM THIS SYSTEM
ARE EXPECTED TO APPROACH OR EVEN EXCEED TYPICAL MONTHLY TOTALS ACROSS PARTS OF
THE INTERIOR WEST DURING THE FIRST WEEK OF MAY ALONE. THE SAME HOLDS TRUE FOR
MUCH OF THE SOUTHERN PLAINS AS A COMBINATION OF THIS CUT-OFF LOW AND A STALLED
FRONT ARE EXPECTED TO RESULT IN AN ACTIVE PATTERN DURING THE FIRST HALF OF MAY.
AS SUCH, PROBABILITIES OF ABOVE NORMAL PRECIPITATION WERE INCREASED
SIGNIFICANTLY RELATIVE TO THE HALF MONTH LEAD FOR BOTH THE INTERIOR WEST AND
THE SOUTHERN PLAINS. AN ACTIVE PATTERN IS EXPECTED TO BE ESPECIALLY PROLONGED
FOR THE SOUTHERN PLAINS LEADING TO PROBABILITIES OF ABOVE NORMAL PRECIPITATION
EXCEEDING 60 PERCENT IN SOME AREAS. CONVERSELY, THE AREA FAVORED TO BE DRIER
THAN NORMAL IS EXPANDED EAST TO INCLUDE THE WESTERN GREAT LAKES AS RIDGING IS
EXPECTED TO DOMINATE MUCH OF THE NORTHERN TIER OF THE CONUS FOR MUCH OF THE
MONTH. UNCERTAINTY IS HIGH ALONG THE EASTERN SEABOARD AS A WET PERIOD
ASSOCIATED WITH A FRONTAL BOUNDARY IS EXPECTED EARLY IN MAY FOLLOWED BY A DRY
PERIOD. THIS CHANGEABLE PATTERN LEADS TO AN EQUAL CHANCES (EC) FORECAST FOR THE
EAST COAST. FARTHER TO THE NORTH AND WEST, AN ACTIVE PERIOD IS LIKELY FOR MUCH
OF ALASKA AS A PERSISTENT LOW PRESSURE SYSTEM IS EXPECTED TO LINGER IN THE GULF
OF ALASKA FOR MUCH OF EARLY MAY. THIS SHOULD FAVOR ABOVE NORMAL PRECIPITATION
FOR MUCH OF SOUTHEASTERN ALASKA SOUTHWARD TO PARTS OF THE PACIFIC NORTHWEST.
PROBABILITIES OF ABOVE NORMAL PRECIPITATION EXCEED 50 PERCENT FOR SOUTHEAST
ALASKA AS INCREASED WETNESS IS FAVORED TO PERSIST DEEPER INTO MAY IN CPC’S
WEEKS 3-4 OUTLOOKS.
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****** PREVIOUS MID-MONTH DISCUSSION BELOW ******
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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.
THE NEXT MONTHLY OUTLOOK...FOR JUN ... WILL BE ISSUED ON THU MAY 15 2025
THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1991-2020 BASE PERIOD.
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