819
FXUS02 KWBC 050653
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
253 AM EDT MON MAY 5 2025
VALID 12Z THU MAY 08 2025 - 12Z MON MAY 12 2025
...MID TO LATE WEEK HEAVY RAINFALL POTENTIAL FOR THE CENTRAL GULF
COAST INTO THE SOUTHEAST...
..OVERVIEW
A WEAKENING UPPER LOW OVER THE CENTRAL PLAINS WILL SHIFT SLOWLY
EASTWARD, EVENTUALLY SETTLING OVER/NEAR THE SOUTHEAST THROUGH NEXT
WEEKEND. THIS SHOULD ALLOW FOR A STATIONARY OR VERY SLOW MOVING
FRONTAL BOUNDARY TO REMAIN DRAPED ACROSS THE SOUTHEAST WITH SOME
DAILY CHANCES FOR HEAVY RAINFALL AS ANOMALOUS MOISTURE POOLS ALONG
THE BOUNDARY. MEANWHILE, A NORTHERN STREAM SHORTWAVE MAY BRIEFLY
CLOSE OFF A LOW OVER THE NORTHEAST, BUT WITH A LOT OF UNCERTAINTY
IN WHAT OR ANY SENSIBLE WEATHER IMPACTS THIS MAY BRING. ELONGATED
TROUGHING OFF THE WEST COAST, STEMMING FROM AN UPPER LOW MOVING OUT
OF THE GULF OF ALASKA, WILL MOVE INTO THE WEST NEXT SUNDAY, WITH
SOME AGREEMENT ON A CLOSED LOW OVER THE PACIFIC NORTHWEST/NORTHERN
CALIFORNIA REGION EARLY NEXT WEEK. THIS PUSHES UPPER RIDGING
DOWNSTREAM IN THE PLAINS STATES.
..GUIDANCE/PREDICTABILITY ASSESSMENT
WHILE MODEL GUIDANCE AGREES IN PRINCIPLE ON THE LARGER SCALE
FEATURES AND EVOLUTION DESCRIBED ABOVE, UNCERTAINTY IN THE DETAILS
STILL PRODUCE SENSIBLE WEATHER DIFFERENCES. AS EARLY AS DAY 4,
MODELS CONTINUE TO STRUGGLE WITH A CUTOFF LOW OVER THE LOCATION AND
TRACK OF A CUTOFF LOW OVER THE NORTHEAST. THE ECMWF WAS THE
OUTLIER THIS EVENING, SHOWING A LOW MUCH FARTHER SOUTH OVER THE
MID- ATLANTIC VERSUS THE BETTER CONSENSUS WHICH IS FARTHER NORTH
AND OVER THE NORTHEAST. THE UKMET WAS THE FARTHEST NORTH. STILL
SOME RUN TO RUN VARIABILITY IN THE MODELS SO THE EVOLUTION OF THIS
FEATURE REMAINS VERY LOW CONFIDENCE STILL.
ELSEWHERE, THE MODELS SHOW AGREEMENT THAT THE UPPER LOW INITIALLY
OVER THE CENTRAL/SOUTHERN PLAINS WILL DRIFT SLOWLY EAST OVER THE
SOUTHEAST, BUT WITH PLENTY OF UNCERTAINTY IN THE TIMING. THE ECMWF
WAS THE FASTEST TO RACE THIS FEATURE OFF THE SOUTHEAST BY EARLY
NEXT WEEK. OUT WEST, THE CMC CONTINUES TO BE THE OUTLIER WITH
KEEPING TROUGHING WELL OFF THE WEST COAST AS A RESULT OF AN EARLIER
CUT OFF UPPER LOW DRIFTING SOUTHWESTWARD. THE ECMWF, GFS, AND THE
ENSEMBLE MEANS SHOW TROUGHING MOVING INTO THE WEST, WITH SOME
INDICATIONS THAT A BROAD CLOSED LOW MAY BE PRESENT OVER THE WEST
COAST BY NEXT MONDAY.
THE WPC FORECAST FOR TONIGHT USED A BLEND OF THE DETERMINISTIC
MODELS WITH THE ENSEMBLE MEANS, OUTSIDE OF THE UKMET WHICH WAS MUCH
FARTHER NORTH WITH THE EARLY PERIOD UPPER LOW OVER THE NORTHEAST.
INCREASED THE WEIGHTING OF THE ENSEMBLE MEANS FROM 30 TO 70 PERCENT
THROUGH THE PERIOD WHICH HELPS MITIGATE THE SMALLER SCALE
DIFFERENCES, ESPECIALLY LATE PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
A STATIONARY FRONTAL BOUNDARY THROUGH THE SOUTHEAST TO CENTRAL
GULF COAST WILL CONTINUE SOME SORT OF HEAVY RAINFALL THREAT ALONG
THE BOUNDARY WITHIN AN AREA OF ANOMALOUS MOISTURE. HOWEVER, MODEL
SPREAD, DRIER ANTECEDENT CONDITIONS, AND HIGHER FLASH FLOOD
GUIDANCE LIMITS THE OVERALL FLASH FLOODING POTENTIAL. AS SUCH, HELD
WITH MARGINAL RISKS ON THE DAYS 4 AND 5 EROS (THURSDAY AND FRIDAY)
FOR TONIGHT. AREAS OF RAIN ARE ALSO LIKELY ACROSS THE CENTRAL
PLAINS TO MIDDLE MISSISSIPPI VALLEY INTO THURSDAY AND LINGERING
INTO FRIDAY IN THE LOWER MISSISSIPPI VALLEY. AREAS OF RAIN ARE ALSO
POSSIBLE IN THE NORTHEASTERN U.S. AT TIMES LATER THIS WEEK INTO
THE WEEKEND, BUT AMOUNTS ARE HIGHLY DEPENDENT ON UPPER LOW
EVOLUTION.
THE UPPER LOW OVER THE SOUTHERN PLAINS REGION EARLY IN THE PERIOD
WILL RESULT IN LINGERING BELOW NORMAL TEMPERATURES FOR THE SOUTH-
CENTRAL PLAINS WHERE DAYTIME HIGHS COULD BE 5-10 DEGREES BELOW
NORMAL. THIS SHOULD MODERATE WITH TIME BUT MAY STILL REMAIN
MODESTLY BELOW NORMAL INTO LATE WEEK FOR THE SOUTHERN PLAINS. UPPER
TROUGHING/LOW OVER THE NORTHEAST KEEPS TEMPERATURES NEAR OR BELOW
NORMAL AS WELL. UPPER RIDGING BUILDING OVER THE WEST AS THE UPPER
LOW SHIFTS EAST WILL ALLOW FOR EXPANDING COVERAGE OF ABOVE NORMAL
TEMPERATURES THERE AS THE WEEK PROGRESSES, INCLUDING 100 DEGREE
TEMPERATURES IN THE DESERT SOUTHWEST. ABOVE AVERAGE TEMPERATURES
WILL STRETCH INTO THE NORTHERN TIER AS WELL, WITH HIGHS REACHING
THE 70S AND 80S IN THE NORTHERN PLAINS TO UPPER MIDWEST.
SANTORELLI
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION FORECAST (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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