202
FOUS30 KWBC 030100
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
900 PM EDT FRI MAY 2 2025
DAY 1
VALID 01Z SAT MAY 03 2025 - 12Z SAT MAY 03 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHERN PLAINS, LOWER MISSISSIPPI, TO THE SOUTHERN
APPALACHIANS...
01Z UPDATE...
BIGGEST ADJUSTMENT TO THE PREVIOUS OUTLOOK WAS TO TRIM AWAY THE
NORTHWESTERN EXTENT OF THE PREVIOUS OUTLOOKS ACROSS NORTHERN TEXAS
WHERE THE HEAVY RAIN AND FLOODING THREAT HAS ENDED AND WHERE
ADDITIONAL DEVELOPMENT IS NOT EXPECTED.
A SLIGHT RISK REMAINS IN PLACE FROM SOUTHWEST THROUGH SOUTH-
CENTRAL TEXAS INTO SOUTHWEST LOUISIANA WHERE LOCALLY HEAVY SHOWERS
WILL CONTINUE THROUGH THE EVENING HOURS -- PRODUCING ADDITIONAL
AREAS OF FLASH FLOODING. REFER TO WPC MPD #212 FOR ADDITIONAL
INFORMATION REGARDING THE NEAR-TERM HEAVY RAIN AND FLOODING THREAT
ACROSS THIS AREA.
FURTHER TO THE EAST, EXTENDED THE PREVIOUS SLIGHT RISK AREA SOUTH
INTO PARTS OF SOUTHEASTERN LOUISIANA, SOUTHERN MISSISSIPPI,
ALABAMA, AND THE FAR WESTERN FLORIDA PANHANDLE. RECENT RUNS OF THE
HRRR AND SOME OF THE OTHER CAM GUIDANCE SHOW SLOW-MOVING CONVECTION
DEVELOPING LATER THIS EVENING ALONG AN AXIS OF ENHANCED
CONVERGENCE NEAR THE COAST, WITH POSSIBLE MERGERS WITH THE UPSTREAM
CONVECTION NOW MOVING ACROSS THE LOWER MISSISSIPPI VALLEY. THE 18Z
HREF SHOWS HIGH NEIGHBORHOOD PROBABILITIES FOR EVENING/OVERNIGHT
ACCUMULATIONS EXCEEDING 3 INCHES CENTERED NEAR MOBILE BAY.
SIMILAR TO AREAS BACK TO THE WEST, THE SLIGHT RISK WAS TRIMMED OUT
OF THE TENNESSEE VALLEY WHERE THE RAINFALL HAS ENDED. A SLIGHT
RISK WAS MAINTAINED FROM CENTRAL ALABAMA NORTHEASTWARD INTO THE
SOUTHERN APPLACHIANS WHERE CONVECTION CONTINUES TO DEVELOP AND MOVE
AHEAD OF AN UPSTREAM FRONT.
PEREIRA
DAY 2
VALID 12Z SAT MAY 03 2025 - 12Z SUN MAY 04 2025
....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE GULF
COAST REGION INTO PARTS OF THE NORTHEAST, EXTREME DEEP SOUTH TEXAS,
AND THE SACRAMENTO MOUNTAINS OF NEW MEXICO...
..20Z UPDATE
THE MARGINAL RISK ACROSS PORTIONS OF THE EAST COAST WAS EXPANDED
EAST TO INCLUDE PORTIONS OF THE I-95 CORRIDOR THROUGH DC AND
BALTIMORE, THE PIEDMONT OF THE CAROLINAS, AND EXPANDED WEST INTO
EAST CENTRAL ILLINOIS. A NEW MARGINAL RISK WAS ISSUED FOR THE
SACRAMENTO MOUNTAINS OF NEW MEXICO.
DUE TO UNCERTAINTIES WITH POTENTIAL TRAINING STORMS UP THE BLUE
RIDGE OF VA INTO PA, INCLUDING IMPACTS INTO THE DC AND BALTIMORE
METROS, A LOW-END MARGINAL EXPANDED TO INCLUDE THAT PORTION OF THE
I-95 CORRIDOR WITH THIS UPDATE. MOST OF THE GUIDANCE SUGGESTS ANY
HEAVIER RAINS AND TRAINING STORMS WILL BE WEST OF THE METRO, AND
THE ONGOING SEVERE DROUGHT WILL MITIGATE MOST IMPACTS, BUT AN
ISOLATED FLOOD CAN'T BE RULED OUT SHOULD TRAINING STORMS MOVE OVER
THOSE CITIES. GIVEN SOME INSTABILITY EXPECTED INTO SOUTHERN NEW
ENGLAND, THE MARGINAL WAS ALSO EXPANDED INTO WESTERN MA AND CT ON
THE ASSUMPTION THAT NORTHEASTWARD MOVING STORMS MAY PERSIST LONGER
INTO NEW ENGLAND. WRAPAROUND RAIN AROUND THE NORTH SIDE OF A CUTOFF
LOW OVER ILLINOIS HAS RESULTED IN A DECENTLY WELL AGREED UPON
MAXIMUM OF RAINFALL INTO EAST CENTRAL ILLINOIS, SO THE MARGINAL WAS
EXPANDED WEST FOR THAT AS WELL.
THE MARGINAL IN EXTREME DEEP SOUTH TEXAS WAS TRIMMED FROM THE NORTH
TO EXCLUDE AREAS WITH VERY HIGH FFGS. IT APPEARS INCREASINGLY
LIKELY THAT THE STORMS IMPACTING THAT AREA, IF THEY TRAIN, WILL BE
SOUTH OF THE BORDER, BUT SOME POTENTIAL REMAINS INTO MCALLEN AND
BROWNSVILLE FOR TRAINING STORMS, SO THE MARGINAL WAS LEFT IN PLACE
FOR THOSE URBAN CENTERS.
IN COORDINATION WITH ABQ/ALBUQUERQUE WFO, A MARGINAL WAS INTRODUCED
FOR THE SACRAMENTO MOUNTAINS FOR THE POTENTIAL FOR NEARLY
STATIONARY STORMS TIED TO THE TERRAIN IMPACTING OLD BURN SCAR AREAS
NEAR RUIDOSO, NM.
WEGMAN
..PREVIOUS DISCUSSION
THE FOCUS FOR EXCESSIVE RAINFALL WILL SHIFT EASTWARD AS A CLOSED
MID-LEVEL CIRCULATION CENTER TAKES SHAPE OVER THE NATION'S MID-
SECTION. THE MID- AND UPPER-LEVEL FLOW BACKS WITH TIME FROM THE
GULF COAST NORTHWARD ACROSS PARTS OF THE TENNESSEE AND OHIO
VALLEYS. INITIALLY...THIS ALLOWS DEEPER MOISTURE TO STREAM
NORTHWARD. BUT IT ALSO RESULTS IN THE SURFACE/LOW LEVEL FRONT TO
MOVE EASTWARD MORE QUICKLY LATER IN THE PERIOD...WITH GENERALLY A
LOW-END RISK OF FLOODING FROM THE GULF COAST NORTHWARD. THE 02/00Z
SUITE OF NUMERICAL GUIDANCE HINT THAT THERE COULD BE SOME 1 INCH TO
PERHAPS 2 INCH AMOUNTS WHERE FRONTOGENETIC FORCING ALIGNS
FAVORABLY IN BETWEEN THE GULF AND THE OHIO VALLEY...BUT THE SIGNAL
FOR EXCESSIVE RAINFALL SHOWED LITTLE RUN TO RUN / MODEL TO MODEL
CONSISTENCY.
THERE IS ALSO A MARGINAL RISK OF EXCESSIVE RAINFALL OVER FAR
SOUTHERN PORTION OF TEXAS...WHERE THE SOUTHERN END OF THE COLD HAS
STALLED ITS SOUTHWARD PROGRESSION AND RETURN FLOW OF GULF MOISTURE
HAS BEGUN. SEVERAL OF THE HIGH RES ENSEMBLE HIGHLIGHT THIS AREA
WITH QPF IN THE UPPER PERCENTILES ALTHOUGH THE CONSENSUS IS LESS
THAN UNANIMOUS IN AMOUNTS OR PLACEMENT. WITH SOUNDINGS SHOWING
WARM CLOUD PROCESSES THROUGH A DEEP LAYER AND THE CAPE PROFILE IS
TALL AND SKINNY...INTRODUCED A MARGINAL RISK HERE.
BANN
DAY 3
VALID 12Z SUN MAY 04 2025 - 12Z MON MAY 05 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE
EASTERN UNITED STATES AND SOUTHERN ROCKIES ...
..20Z UPDATE
THE MARGINAL RISK ACROSS THE EAST COAST WAS EXPANDED GREATLY TO
INCLUDE MUCH OF THE NORTHEAST, MID-ATLANTIC AND COASTAL CAROLINAS,
WITH THE OTHER MARGINAL EXPANDED WELL WEST TO INCLUDE PORTIONS OF
SOUTHWEST COLORADO, SOUTHERN UTAH, AND EASTERN NEVADA WITH THIS
UPDATE.
THE MARGINAL ACROSS THE EAST WILL BE FOR CONTINUE TRAINING SHOWERS
AND STORMS INTO NEW ENGLAND, WITH A MAXIMUM OF RAINFALL LIKELY NEAR
THE CATSKILLS AND POCONOS OF NY AND PA, RESPECTIVELY. RATES SHOULD
REMAIN LOW ENOUGH WITH SOME BREAKS IN THE RAIN THAT AMOUNTS REMAIN
WITHIN MARGINAL THRESHOLDS, BUT SHOULD THE DAY 2/SATURDAY RAINFALL
OVERPERFORM IN THIS AREA OR IF THE FORECAST RAIN COMES UP FOR
SUNDAY, THEN A TARGETED SLIGHT RISK MAY BE NEEDED. OCCASIONAL
STORMS WITH MUCAPE INSTABILITY VALUES BETWEEN 500 AND 1,000 J/KG
ARE MORE LIKELY TO IMPACT MORE OF THE I-95 CORRIDOR FROM RALEIGH,
NC THROUGH NYC. DROUGHT CONDITIONS ARE VERY LIKELY TO TEMPER ALL
BUT THE MOST PERSISTENT RAINS, BUT GIVEN THE SENSITIVITIES IN THE
URBAN CORRIDOR, THE MARGINAL WAS EXPANDED TO ACCOUNT FOR POTENTIAL
TRAINING STORMS.
THE MARGINAL RISK OUT WEST WAS EXPANDED WITH A DEEP BUT SLOW MOVING
UPPER LEVEL LOW AND TROUGH MOVING ACROSS THE 4-CORNERS REGION,
DRAWING SOME GULF MOISTURE WELL NORTHWEST AND INTO THE AREA, WHERE
TERRAIN WILL CAUSE LOCALIZED UPSLOPE. ROCKY TERRAIN WILL ALSO FAVOR
RAPID DEVELOPMENT OF FLASH FLOODING IN THE LOCAL AREAS WHERE THE
RAIN IS MOST PERSISTENT. THE HIGHEST ELEVATIONS WILL SEE MOSTLY
SNOW FROM THIS EVENT, BUT MOST OF THE AREA SHOULD SEE RAIN, WHICH
IS THE RATIONALE FOR THE EXPANSION OF THE MARGINAL. THE SAN JUANS
WILL HAVE SOME OF THE HEAVIEST PRECIPITATION, WHICH SHOULD LOWER
SNOW LEVELS LOCALLY ENOUGH TO CARVE THAT AREA OUT OF THE MARGINAL
WITH THIS UPDATE.
WEGMAN
..PREVIOUS DISCUSSION
THE RISK OF EXCESSIVE RAINFALL PERSISTS ACROSS PARTS OF THE MID-
ATLANTIC AND SOUTHEAST US AS A BROAD UPPER TROUGH CONTINUES TO MAKE
ITS WAY EASTWARD ON DAY 3. DEEPEST MOISTURE OF 1.25 TO 1.5 INCHES
WILL BE EVENTUALLY BE SHUNTED OFF-SHORE LATE IN THE PERIOD. UNTIL
THEN...ISOLATED DOWNPOURS ARE POSSIBLE WITH SPAGHETTI PLOTS OF
2 AND 3-INCHES OF RAIN IN 24 HOURS MAINLY BEING PRODUCED BY MODELS
WITH THE ARW CORE...BUT ENOUGH MEMBERS FROM THE NMM CORE AND FROM
THE GEFS TO WARRANT A MARGINAL.
THERE IS ALSO A MARGINAL RISK AREA OVER PARTS OF NEW MEXICO AGAIN
AS MOISTURE CONTINUE TO SPREAD NORTHWARD AND WESTWARD FROM THE
GULF. AFTER 00Z...THE FLOW ALOFT BETWEEN THE WESTERLY SUBTROPICAL
JET AND A JET STREAK AND LOW- AND MID-LEVELS BECOME INCREASINGLY
DIFFLUENT WITH HEIGHT FALLS BEGINNING AHEAD OF AN APPROACHING
CLOSED LOW FROM THE WEST. THIS...ALONG WITH MOISTURE AND A LOW
LEVEL BOUNDARY ALREADY IN PLACE...SHOULD SUPPORT LATE DAY AND
EVENING STORMS THAT MAY PRODUCE LOCALLY HEAVY RAINFALL RATES.
BANN
DAY 1 THREAT AREA: HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/94EPOINTS.TXT
DAY 2 THREAT AREA: HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/98EPOINTS.TXT
DAY 3 THREAT AREA: HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/99EPOINTS.TXT
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