657
FOUS30 KWBC 291910
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
310 PM EDT WED OCT 29 2025
DAY 1
VALID 16Z 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...
16Z UPDATE: MAIN CHANGE WAS REMOVAL OF THE VALLEY AREAS OF EASTERN
TN WHERE AN AREAL MIN IN QPF IS FORECAST ACROSS ALL GUIDANCE
LEADING TO LIMITED FLASH FLOOD CONCERNS. REMAINDER OF THE FORECAST
IS ON TRACK WITH THE PRIMARY MAXIMA STILL SITUATED IN THE CENTRAL
AND SOUTHERN APPALACHIANS AND NEIGHBORING BLUE RIDGE IN VA.
NEIGHBORHOOD PROBS FROM THE LATEST 12Z HREF WERE INDICATIVE OF SOME
>3" MAXIMA SITUATED OVER THE NORTHERN NECK OF VA WITH
PROBABILITIES UPTICK TO 25-50% IN-OF THE BLUE RIDGE EXTENSION JUST
EAST OF I-81. THIS MAKES SENSE SYNOPTICALLY WITH THE INCREASING
UPSLOPE COMPONENT INITIATING OVERNIGHT INTO THE END OF THE PERIOD
WITH A MODEST INSTABILITY REGIME DEVELOPING ALONG THE TERRAIN AND
POINTS EAST THANKS TO THE PROJECTED THETA_E ADVECTION PATTERN
MATERIALIZING AS THE ULL PIVOTS EASTWARD AND WE RESIDE IN
PERSISTENT ONSHORE FETCH FROM THE ATLANTIC. THANKS TO DRY
ANTECEDENT CONDITIONS LEADING INTO THE PERIOD, THE SETUP IS CURBED
TO BE MORE IN LINE WITH A MRGL RISK THRESHOLD, THUS MAINTAINED
GENERAL CONTINUITY OUTSIDE THE SMALL CHANGE IN TN AND THE WESTERN
FRINGES OF THE RISK AREA ACROSS CENTRAL TN AND KY.
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. HREF
NEIGHBORHOOD PROBS FOR >2" ARE RELATIVELY HIGH IN-OF THE BLUE
RIDGE FROM VIRGINIA DOWN INTO THE WESTERN CAROLINAS (60-90%) WITH A
VAST MAJORITY OF THE RAIN 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 LEADING TO
A GREATER POTENTIAL FOR THAT LOW- TOPPED CONVECTION TO IMPACT
THESE ZONES. A MARGINAL RISK AREA REMAINS IN EFFECT FOR THIS PART
OF THE NATION.
CAMPBELL/KLEEBAUER
DAY 2
VALID 12Z THU OCT 30 2025 - 12Z FRI OCT 31 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE MID ATLANTIC AND NORTHEAST...
20Z UPDATE: THE CURRENT PATTERN REMAINS CONSISTENT WITHIN GUIDANCE
WITH THE MEAN QPF MAXIMA BETWEEN 1.25-2.5", LOCAL TO 3" FORECAST
OVER SOUTHEAST PA UP THROUGH PARTS OF NJ, NYC METRO, WESTERN LI,
AND SOUTHWEST CT. MAIN ADJUSTMENT FROM PREVIOUS ISSUANCE IS THE
EXPANSION OF THE MRGL RISK DOWN THROUGH SOUTHEAST PA TO INCLUDE
MORE OF THE PHILADELPHIA METRO AND SURROUNDING SUBURBS. DESPITE
ANTECEDENT DRY SOILS OVERALL ACROSS THE AREA, HIGH URBAN DENSITY
COUPLED WITH ANTICIPATION OF RATES >1"/HR AT TIMES WILL PROMOTE A
GREATER THREAT FOR RUN OFF WITH SOME ISOLATED FLASH FLOOD CONCERNS
IN THOSE AREAS COMPRISED OF MOSTLY AN URBAN FOOTPRINT. 12Z HREF
PROBS ARE GENERALLY ELEVATED (50-90%) FOR AREAS OF >2" OVER MUCH OF
SOUTHEAST AND EASTERN PA INTO THE NORTHERN HALF OF NJ, THE MOST
LIKELY LOCATION FOR FLASH FLOOD PROSPECTS CONSIDERING THE
INSTABILITY PRESENCE COUPLING WITH THE WELL-ABOVE NORMAL PWATS
FORECAST OVER THE REGION. IN COORDINATION WITH THE LOCAL MOUNT
HOLLY WFO COVERING THE AREA OF INTEREST, A MRGL RISK EXPANSION WAS
MADE TO ACCOUNT FOR THE THREAT TOMORROW MORNING AND AFTERNOON.
KLEEBAUER
..PREVIOUS DISCUSSION..
THIS SYSTEM IS FORECAST TO TRACK TO THE NORTHEAST AS THE
ASSOCIATED SURFACE LOW STRENGTHENS OVER THE MID-ATLANTIC ONWARD TO
THE NORTHEAST. HEAVY RAIN WILL ACCOMPANY THE LOW AND OVERSPREAD THE
REGION. 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 PENNSYLVANIA UP
THROUGH NEW JERSEY, NEW YORK CITY METRO, AND WESTERN LONG ISLAND
TO ABOUT THE I-95 CORRIDOR IN CONNECTICUT. A MARGINAL RISK FOR
EXCESSIVE RAINFALL AND ISOLATED FLASH FLOOD CONCERNS IN THAT
URBANIZED CORRIDOR OF THE NORTHEASTERN U.S. REMAINS FOR THIS
PERIOD.
CAMPBELL/KLEEBAUER
DAY 3
VALID 12Z FRI OCT 31 2025 - 12Z SAT NOV 01 2025
...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR NORTHWESTERN
WASHINGTON STATE...
20Z UPDATE: A RELATIVELY STOUT ATMOSPHERIC RIVER WILL SETUP ACROSS
THE PAC NORTHWEST WITH AN ADVECTION OF HIGH (>750 KG/MS) INTO THE
REGION BEGINNING FRIDAY AFTERNOON, CARRYING THROUGH THE LATE
EVENING FRIDAY INTO SATURDAY. PRECIP RATES BETWEEN 0.5-0.75"/HR ARE
FORECAST IN-OF THE OLYMPICS AND SURROUNDING LOCALES DURING THE
HEIGHT OF THE EVENT WITH A GENERAL 0.25-0.5"/HR RATES LIKELY ON
AVERAGE DURING THE PERIOD OF IMPACT. THIS WILL PRODUCE RAINFALL
TOTALS BETWEEN 1-3" WITH UPWARDS OF 4-5" IN THE HIGHER TERRAIN
FOCUSED IN THE OLYMPICS WHERE THE GREATEST UPSLOPE PATTERN WILL
OCCUR WITH THE HIGHER RATES PROGGED. AREAS ALONG THE WESTERN SLOPES
OF THE NORTHERN CASCADES WILL ALSO SEE SOME ENHANCEMENT OF PRECIP
FOR A PERIOD ON FRIDAY EVENING AS THE IVT PULSE PROTRUDES INLAND
AND ALLOWS FOR A FOCUSED SECONDARY MAXIMA IN THE AFOREMENTIONED
AREA. FORECAST RIVERS IN THIS AREA ARE EXPECTED TO RISE INTO ACTION
STAGE DUE TO THE INCOMING RAINFALL, SO THERE'S A LOW END THREAT OF
LOCALIZED FLOODING WITHIN THE CONFINES OF THESE RIVER LOCATIONS.
CONSIDERING THE CONSISTENCY WITHIN GUIDANCE ON TOTALS AND
EXPECTATION FOR SOME ENHANCED RATES TO GENERATE RIVER RISES AND
MINOR FLOODING, A MRGL RISK WAS MAINTAINED OVER THE OLYMPIC
PENINSULA OVER INTO THE WESTERN SIDE OF THE NORTHERN CASCADES.
KLEEBAUER
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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