154
FOUS30 KWBC 282352
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
752 PM EDT TUE OCT 28 2025
DAY 1
VALID 01Z WED OCT 29 2025 - 12Z WED OCT 29 2025
THE PROBABILITY OF RAINFALL EXCEEDING FLASH FLOOD GUIDANCE IS LESS
THAN 5 PERCENT.
HURLEY
DAY 2
VALID 12Z WED OCT 29 2025 - 12Z THU OCT 30 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE
SOUTHERN AND CENTRAL APPALACHIANS AND SURROUNDING PORTIONS OF THE
OHIO/TENNESSEE VALLEYS...
20Z UPDATE: THE PRIOR FORECAST REMAINS ON TRACK WITH LITTLE
DEVIATION IN THE QPF DISTRIBUTION FOCUSED OVER THE CENTRAL AND
SOUTHERN APPS INTO THE OHIO VALLEY AND MID ATLANTIC. 12Z HREF
NEIGHBORHOOD PROBS FOR >2" ARE RELATIVELY HIGH IN-OF THE BLUE RIDGE
FROM VA DOWN INTO THE WESTERN CAROLINAS (60-90%) WITH A VAST
MAJORITY OF THE PRECIP COMING FROM SHALLOW CONVECTIVE PROCESSES
FOCUSED WITHIN THE TERRAIN. LARGE SCALE FORCING ACROSS THE
AFOREMENTIONED AREAS WILL BE THE PRIMARY DRIVER FOR THE HEAVY RAIN
SCENARIO, HOWEVER A TONGUE OF ELEVATED THETA_E IS EXPECTED TO
ADVECT OFF THE ATLANTIC INTO THE CENTRAL APPS/BLUE RIDGE BY THE END
OF THE FORECAST CYCLE LEADING TO A GREATER POTENTIAL FOR THAT LOW-
TOPPED CONVECTION TO IMPACT THESE ZONES. THAT'S LIKELY THE CASE FOR
THE PROB FIELDS BEING MORE ELEVATED IN THESE ZONES JUST DUE TO A
MORE FAVORABLE ENVIRONMENT COINCIDENT FOR THOSE CONVECTIVE SCHEMES
AND SUBSEQUENT HEAVIER RAINFALL FOOTPRINT. IN ANY CASE, THE SETUP
STILL FAVORS A MORE MODEST MRGL RISK PROSPECT FOR FLASH FLOODING AS
DRIER SOILS SHOULD INITIALLY HELP CURB SOME OF THE THREAT WITH A
MORE LOCALIZED FOCUS OF IMPACT. THUS, THE MRGL RISK WAS MAINTAINED
WITH ONLY SOME MINOR ADJUSTMENTS TO REFLECT THE QPF MAX/MIN
DISTRIBUTION SPATIALLY.
KLEEBAUER
..PREVIOUS DISCUSSION..
RAINFALL IS EXPECTED TO OVERSPREAD THE TENNESSEE/OHIO VALLEY WITH
ANOMALOUS LOW- LEVEL MOISTURE TRANSPORT DRIVING EAST-SOUTHEAST
MOISTURE TRANSPORT INTO THE SOUTHERN/CENTRAL APPALACHIANS AS A
CLOSED UPPER LOW SWIVELS FROM THE MID-SOUTH TO THE OHIO VALLEY.
MUCH OF THIS PART OF THE COUNTRY WILL EXPERIENCE BENEFICIAL
MOISTURE; HOWEVER THERE WILL BE EMBEDDED LOCATIONS THAT HAVE THE
POTENTIAL FOR INTRA-HOUR RATES OF 1-1.5 INCHES/HOUR THAT COULD
RESULT IN LOCALIZED FLASH FLOODING. THIS IS DESPITE LIMITED
INSTABILITY (SIMILAR TO DAY 2 ACROSS THE MID- SOUTH), AS THE
DYNAMICS OF THE CLOSED LOW (NOTABLE PV ANOMALY WITH ENHANCED
DIVERGENCE ALOFT VIA LEFT EXIT REGION OF ~130 KT JET STREAK @ 250
MB) MAY RESULT IN LOCALIZED 2" EXCEEDANCE IN THE OHIO/TENNESSEE
VALLEY (WITH TERRAIN FORCING PRIMARILY DRIVING ANY LOCALIZED 2"
EXCEEDANCE ALONG/EAST OF THE SOUTHERN/CENTRAL APPALACHIANS).
CAMPBELL/CHURCHILL
DAY 3
VALID 12Z THU OCT 30 2025 - 12Z FRI OCT 31 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE
SOUTHERN PORTION OF THE NORTHEAST...
20Z UPDATE: OUR SYSTEM WILL NAVIGATE TO THE NORTHEAST WITH A
STRENGTHENING SURFACE LOW MOVING THROUGH THE INTERIOR MID ATLANTIC,
EVENTUALLY SIGHTS ON THE NORTHEAST BY THE END OF THE FORECAST
CYCLE. HEAVIEST RAINFALL WILL LIKELY OCCUR ACROSS SOUTHEASTERN PA
UP THROUGH NORTHERN AND CENTRAL NJ, SOUTHERN NY STATE (NYC/LI
INCLUDED), INTO SOUTHERN NEW ENGLAND. THE BEST THREAT FOR
CONVECTIVE ENHANCEMENT LEADING TO BETTER RATES >1"/HR AND SOME
MINOR TRAINING OFF STEADY SOUTHEAST FLOW OFF THE ATLANTIC WILL
OCCUR FROM SOUTHEAST PA UP THROUGH NJ, NYC METRO, AND WESTERN LI TO
ABOUT THE I-95 CORRIDOR IN CT. THIS AREA HAS A FAVORABLE FFG
EXCEEDANCE MARKER DUE TO THE WIDESPREAD URBANIZATION FOOTPRINT
LEADING TO RUN OFF CAPABILITIES. THE FORWARD PROPAGATION OF THE
PRECIP WILL LIKELY MITIGATE THE WORST IMPACT SCENARIOS, BUT STILL
RESIDES WITHIN THE LOWER TO MIDDLE THRESHOLD OF THE MRGL RISK
CATEGORY FOR FLASH FLOOD CONCERNS AS WE ADD THAT MORE FAVORABLE
CONVECTIVE ELEMENT. PWATS BETWEEN 2-3 DEVIATIONS ABOVE NORMAL ALSO
ENHANCE THE PROBABILITY FOR MORE EFFICIENT RAINFALL PROSPECTS, SO
EVEN WITH A WINDOW ONLY 6-9 HRS. FOR GENERAL IMPACT, THIS WOULD
STILL BE ENOUGH FOR PERHAPS SOME ISOLATED FLASH FLOOD CONCERNS IN
THAT URBANIZED CORRIDOR OF THE NORTHEASTERN U.S. THE MRGL WAS
ADJUSTED TO REFLECT THE LATEST QPF TRENDS WITH THE BIGGEST
EXPANSION OCCURRING ALONG THE I-95 CORRIDOR IN SOUTHWEST CT.
KLEEBAUER
..PREVIOUS DISCUSSION..
THE SYSTEM MENTIONED FOR THE DAY 2 PERIOD WILL CONTINUE TO ADVANCE
UP THE EASTERN SEABOARD DIRECTING WIDESPREAD RAIN TO THE NORTHEAST.
GUIDANCE IS SUGGESTING THE HIGHEST RAINFALL ACCUMULATIONS WILL
FOCUS OVER NORTHERN NEW JERSEY AND SOUTHEAST NEW YORK WHERE WPC
HAS AREAL AVERAGES OF 1.5-2.5 INCHES FORECAST FOR THIS PERIOD. THIS
PART OF THE REGION IS WHERE THE BEST POTENTIAL FOR REACHING OR
EXCEEDING LOCAL FFG GUIDANCE SO A MARGINAL RISK AREA REMAINS IN
EFFECT FOR PORTIONS OF NEW JERSEY, PENNSYLVANIA, NEW YORK, AND
CONNECTICUT.
CAMPBELL
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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