279
FOUS30 KWBC 252029
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
429 PM EDT SAT OCT 25 2025
DAY 1
VALID 16Z SAT OCT 25 2025 - 12Z SUN OCT 26 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
EASTERN TEXAS INTO CENTRAL ARKANSAS AND WESTERN MISSISSIPPI...
..16Z UPDATE
THE MARGINAL RISK AREA OVER THE NORTHWEST COAST REMAINS MOSTLY
UNCHANGED.
IN THE SOUTHERN PLAINS/LOWER MISSISSIPPI VALLEY, RIPPLES OF ENERGY
WILL ROTATE AROUND THE BASE OF A MID-LEVEL LOW HELPING TO GENERATE
THUNDERSTORM ACTIVITY ACROSS PORTIONS OF EASTERN TEXAS, LOUISIANA
AND INTO MISSISSIPPI TODAY. A PRECEDING LINE OF STORMS FROM THIS
MORNING SHOULD COLLAPSE AND DISSIPATE BY THIS AFTERNOON.
A COMPLEX OF STORMS WILL LIKELY DEVELOP OVER EASTERN TEXAS LATER
THIS AFTERNOON AND PROPAGATE EASTWARD INTO ARKANSAS, LOUISIANA AND
MISSISSIPPI THIS EVENING. THE HEAVIEST RAINFALL IS EXPECTED TO
OCCUR BETWEEN 00Z AND 09Z WITHIN A MOISTURE RICH ENVIRONMENT
(1.75-2.25IN. PWAT--90TH PERCENTILE). THERE WILL ALSO BE
SUFFICIENT INSTABILITY (500-1000J/KG ML CAPE) OVER MUCH OF THE
SLIGHT RISK AREA. HREF NEIGHBORHOOD PROBABILITIES OF EXCEEDING 5IN.
AND 3IN. IN 24 HOURS HAVE INCREASED OVER PARTS OF SOUTHEASTERN
ARKANSAS/NORTHWESTERN MISSISSIPPI, WHICH SUPPORTS THE EXPANSION OF
THE SLIGHT RISK INTO THOSE AREAS.
KEBEDE
..PREVIOUS DISCUSSION
MULTIPLE ROUNDS OF HEAVY SHOWERS AND THUNDERSTORMS ARE EXPECTED TO
IMPACT THE BROADER NORTHWEST GULF COAST REGION THIS PERIOD, WITH
ONE INITIAL AXIS OF ON-GOING CONVECTION MOVING ACROSS PARTS OF
EASTERN/SOUTHEASTERN TEXAS AND ADVANCING ACROSS WESTERN LOUISIANA
AND SOUTHERN ARKANSAS. CONVECTION PRESUMABLY IS INTERACTING WITH A
40 KT SOUTHERLY LOW-LEVEL JET OFF THE WESTERN GULF. PRECIPITABLE
WATER VALUES AT OR ABOVE 1.75 INCHES AND MUCAPE VALUES LOCALLY OF
2000 J/KG WILL SUPPORT HIGH RAINFALL RATES POTENTIALLY EXCEEDING 2
INCHES/HOUR WITH THE STRONGER STORMS.
ADDITIONAL ORGANIZED CONVECTION IS EXPECTED LATER TODAY/TONIGHT
WITH THE ARRIVAL OF AN UPPER- LEVEL JET STREAK IN THE SUBTROPICAL
STREAM WHICH INTERACTS WITH THE SOUTHERN STREAM CLOSED LOW/TROUGH
AXIS CROSSING THE SOUTHERN PLAINS. EVEN THOUGH ANTECEDENT
CONDITIONS ARE QUITE DRY, THE CONCERN FOR MULTIPLE ROUNDS OF
CONVECTION WHICH COMBINED MAY YIELD SOME 3 TO 5+ INCH TOTALS, WILL
PROBABLY BE ENOUGH TO SUPPORT A THREAT FOR SCATTERED AREAS OF FLASH
FLOODING. THE MORE SENSITIVE URBANIZED LOCATIONS WILL BE AT
GREATEST RISK FOR IMPACTS.
..PACIFIC NORTHWEST AND NORTHWEST CALIFORNIA
MULTIPLE ROUNDS OF MOISTURE TRANSPORT INTO THE COASTAL RANGES WILL
CONTINUE AS AN ATMOSPHERIC RIVER ACTIVITY CONTINUES...WITH GREATEST
RATES/ACCUMULATION FROM LATER THIS MORNING INTO THE AFTERNOON.
LOCALLY A FEW ADDITIONAL INCHES OF RAIN WILL BE POSSIBLE FOR THE
WINDWARD SLOPES OF THE TERRAIN, BUT GIVEN THE EARLY-SEASON AND
RELATIVELY MODEST NATURE OF THIS ATMOSPHERIC RIVER ACTIVITY, ANY
FLOODING CONCERNS ARE EXPECTED TO BE ISOLATED AT BEST.
BANN
DAY 2
VALID 12Z SUN OCT 26 2025 - 12Z MON OCT 27 2025
..THERE IS 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
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