973
FXUS02 KWBC 051900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM 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
THE LATEST MODEL GUIDANCE CONTINUES TO SHOW RELATIVELY GOOD
AGREEMENT WITH REGARDS TO THE LARGE SCALE PATTERN THROUGH THE
MEDIUM RANGE PERIOD. THAT BEING SAID, THERE ARE STILL SOME
LINGERING SOURCES OF UNCERTAINTY WITHIN THE FINER DETAILS. ACROSS
THE GREAT LAKES AND NORTHEAST FRIDAY INTO SATURDAY, MODELS CONTINUE
TO STRUGGLE WITH THE EVOLUTION OF A SHARPLY DIGGING TROUGH THAT
BRIEFLY PINCHES OFF INTO A CLOSED LOW BEFORE QUICKLY GETTING SWEPT
OFF INTO THE CANADIAN MARITIMES BY AN UPSTREAM KICKER WAVE. THE
00Z/06Z SUITE OF GUIDANCE VARIED BOTH IN SPEED AND DEPTH, WHICH IS
IMPACTING THE FRONTAL POSITIONS AS WELL AS THE SPATIAL DISTRIBUTION
AND MAGNITUDE OF QPF. COMPARED TO 00Z/06Z, THE 12Z EURO GOT FASTER,
THE 12Z GFS GOT SLOWER, AND THE 12Z CMC GOT FASTER... WITH ALL
THREE MODELS IN DIFFERENT NORTH/SOUTH POSITIONS BY SATURDAY
MORNING. NOTABLY, THE EC-AIFS HAS BEEN FAIRLY STABLE WITH A FASTER
AND MORE NORTHERLY SOLUTION, WHICH INTERESTINGLY ALIGNS WITH THE
LATEST 12Z CMC.
FARTHER SOUTH, THE UPPER LOW INITIALLY OVER THE CENTRAL/SOUTHERN
PLAINS WILL DRIFT SLOWLY SOUTH AND EAST LATER THIS WEEK INTO THE
WEEKEND. MODELS ARE NOW SHOWING A GREATER CONSENSUS OF THIS LOW
ALSO BECOMING CUT OFF FROM THE PREVAILING FLOW AND MEANDERING OVER
THE SOUTHEAST THROUGH AT LEAST EARLY NEXT WEEK. THIS HAS LARGE
IMPLICATIONS TO SENSIBLE WEATHER IMPACTS, INCLUDING THE GROWING
PROBABILITY OF A WETTER AND COLDER WEEKEND ACROSS MUCH OF THE
REGION.
OUT WEST, A DEEP AND HIGHLY AMPLIFIED TROUGH AND CLOSED LOW IS
PROGGED TO SLAM INTO THE WESTERN U.S. LATER THIS WEEKEND INTO EARLY
NEXT WEEK. MODELS ARE IN FAIRLY GOOD AGREEMENT WITH THE DEPTH OF
THE TROUGH, BUT CONTINUE TO DIFFER ON THE SPEED/TIMING OF ITS
INLAND PROGRESSION.
THE WPC FORECAST UTILIZED A GENERAL MODEL BLEND OF THE 00Z/06Z
DETERMINISTIC RUNS OF THE CMC/GFS/EC/UKMET WITH A GRADUAL INCREASE
IN WEIGHTING OF THE 00Z ECENS AND 06Z GEFS BY THE END OF THE
PERIOD. THIS BLEND GAVE A NOD TO CONTINUITY WHILE STILL MAKING
SUBTLE SHIFTS REFLECTIVE OF THE LATEST GUIDANCE.
..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.
MILLER/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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