423
FOUS30 KWBC 260050
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
850 PM EDT SAT OCT 25 2025
DAY 1
VALID 01Z SUN OCT 26 2025 - 12Z SUN OCT 26 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
NORTHWEST GULF COAST & LOWER MISSISSIPPI VALLEY...
AN EAST-WEST BAND OF CONVECTION IS SLOWLY SETTLING SOUTHWARD ACROSS
PORTIONS OF SOUTH-CENTRAL AND SOUTHEAST TX. IT LIES ON THE WESTERN
SIDE OF A REGION OF 850 HPA CONFLUENCE, SOUTHEAST OF A DEEP LAYER
CYCLONE, WHICH HAS PRECIPITABLE WATER VALUES OF 1.5-2", EFFECTIVE
BULK SHEAR OF 35-60 KTS, AND MU CAPE OF 1000-2000 J/KG. ACTIVITY
SHOULD FIRE UP IN THE LOWER MISSISSIPPI VALLEY OVERNIGHT. EVEN
THOUGH ANTECEDENT CONDITIONS ARE QUITE DRY, THE CONCERN IS THAT
OVERNIGHT/EARLY MORNING CONVECTION HAS A ~30% CHANCE OF EXCEEDING
5"+ WITHIN THE 18Z HREF AND 12Z REFS GUIDANCE, WITH THE BEST
OVERLAP FROM THE TECHE/SUGAR GROWING REGION OF LA NORTHEAST INTO
SOUTHWEST MS. THIS SHOULD BE SUFFICIENT FOR AT LEAST SCATTERED
AREAS OF FLASH FLOODING IN THAT AREA, PARTICULARLY IN URBAN CENTERS
WHERE IMPACTS COULD BE ON THE HIGHER END OF A SLIGHT RISK. THE
CONCERN IS FOR TRAINING BAND POTENTIAL, MESOCYCLONE FORMATION
HOLDING UP OTHERWISE PROGRESSIVE CONVECTION, AND CELL MERGERS
WITHIN THIS ENVIRONMENT LEADING TO HOURLY AMOUNTS TO 2.5" AND LOCAL
TOTALS UP TO 6".
ROTH
DAY 2
VALID 12Z SUN OCT 26 2025 - 12Z MON OCT 27 2025
...THERE IS A SLIGHT RISK OVER PORTIONS OF THE CENTRAL GULF
COAST...
A SLIGHT RISK WAS INTRODUCED WITH THIS AFTERNOON'S UPDATE ACROSS
PORTIONS OF COASTAL MISSISSIPPI/ALABAMA AND FAR WESTERN PANHANDLE
OF FLORIDA. STORMS THAT WILL IMPACT PARTS OF THE LOWER MISSISSIPPI
VALLEY SATURDAY NIGHT WILL CONTINUE INTO THE SOUTHEAST AND ALONG
THE CENTRAL GULF COAST ON SUNDAY. MORE ENERGY ROTATING BENEATH A
MID-LEVEL LOW CENTERED OVER THE MIDDLE MISSISSIPPI VALLEY WILL HELP
PROPEL THE CONVECTIVE COMPLEX THROUGH THE SOUTHEAST.
STORMS WILL MOVE INTO A MOISTURE AND INSTABILITY RICH ENVIRONMENT
ACROSS THE IMMEDIATE MISSISSIPPI/ALABAMA/FLORIDA COAST SUNDAY
AFTERNOON/EVENING WHERE THE SLIGHT RISK IS NOW IN PLACE. ALONG THE
IMMEDIATE COAST, PRECIPITABLE WATER VALUES WILL BE BETWEEN 1.5-2",
WHICH WILL BE IN THE 90TH PERCENTILE OF PWATS FOR THIS TIME OF
YEAR. MUCAPE BETWEEN 1000-1500J/KG SHOULD PROVIDE ENOUGH
INSTABILITY TO SUPPORT 1-3IN./HR RAIN RATES IN SOME PLACES. URBAN
AREAS WILL BE ESPECIALLY SUSCEPTIBLE TO RUNOFF FROM EXCESSIVE
RAINFALL.
HREF 40KM AND EAS NEIGHBORHOOD PROBABILITIES OF EXCEEDING 5" AND
3" RESPECTIVELY WILL BE WELL OVER 15% OVER FAR WEST PORTIONS OF
FLORIDA'S PANHANDLE. 40KM PROBABILITIES OF EXCEEDING 5IN. ARE WELL
OVER 30% ACROSS COASTAL MISSISSIPPI AND ALABAMA. CAMS HAVE ALSO
INCREASED THEIR QPF FOOTPRINT WITHIN THE CURRENT SLIGHT RISK AREA
IN RESPONSE TO A GROWING CONSENSUS FOR SLOWER CELL MOTIONS AND
BACKBUILDING STORMS OVER THE IMMEDIATE COAST SUNDAY NIGHT.
KEBEDE
DAY 3
VALID 12Z MON OCT 27 2025 - 12Z TUE OCT 28 2025
...|THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHEAST AND SOUTHERN APPALACHIANS...
..2030Z UPDATE
A SMALL EXPANSION WAS MADE TO THE MARGINAL RISK AREA IN THE
SOUTHEAST IN THE NORTHWEST DIRECTION INTO THE SOUTHERN
APPALACHIANS. THERE'S AN INCREASING QPF TREND IN THE EURO SUITE
OVER THE TERRAIN OF NORTH CAROLINA ON MONDAY.
KEBEDE
..PREVIOUS DISCUSSION
LOW PRESSURE MOVING ACROSS THE SOUTHERN UNITED STATES ON DAY 2
WILL BEGIN TO TAKE A MORE NORTHEASTWARD TRAJECTORY. GIVEN LESS
FAVORABLE LOW LEVEL FLOW AND A MORE STABLE ATMOSPHERE...THE RISK OF
EXCESSIVE RAINFALL WILL BE DIMINISHED. EVEN SO...THE 25/00Z SUITE
OF NUMERICAL GUIDANCE DOES SHOW SPOTTY CONVECTION WITH ISOLATED
BULLS-EYE AMOUNTS OF 2 INCHES OR GREATER MAINLY IN THE CAROLINAS.
THE NAM WAS FAR AND AWAY THE MOST AGGRESSIVE WITH ITS AMOUNTS AND
WAS NOT GIVEN MUCH CONSIDERATION GIVEN THE PLACEMENT OF THE
HEAVIEST RAINFALL IN A REGION WHERE STABLE AIR WAS BANKED UP
AGAINST THE EAST ASPECT OF THE TERRAIN IN RESPONSE TO THE RIDGING
OF SURFACE HIGH PRESSURE TO THE NORTH. WHILE INITIALLY EASY TO
DOWNPLAY THE SPOTTY NATURE OF THE MODEL QPF...THE MACHINE LEARNING
FIRST GUESS ALGORITHM DID POINT THE AREA AS A MARGINAL RISK OF
EXCESSIVE ROUGHLY CO-LOCATED WITH THE WPC DETERMINISTIC QPF. AS A
RESULT...WE OPTED TO SHRINK THE MARGINAL ISSUED ON DAY 4 AND PLACE
IT CLOSER TO THE SOUTHERN PORTION OF THE APPALACHIANS.
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page