864
FOUS30 KWBC 030042
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
842 PM EDT THU OCT 2 2025
DAY 1
VALID 01Z FRI OCT 03 2025 - 12Z FRI OCT 03 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SIERRA, GREAT BASIN AND EASTERN FLORIDA...
01Z UPDATE: THE OVERALL PICTURE HAS CHANGED LITTLE AND THE MESOSCALE
EXPECTATIONS OVER THE TWO RISK AREAS OUTLINED LARGELY REMAINED ON
TRACK FROM THE EARLIER OUTLOOK.
ACROSS FL, LOCALIZED BUT HIGH RAINFALL RATES ARE EXPECTED ACROSS
PORTIONS OF THE EASTERN FLORIDA PENINSULA AN SOUTHEAST FLORIDA
THIS EVENING AND INTO THE OVERNIGHT HOURS. HOURLY RAINFALL RATES OF
2 TO 3 INCHES ARE EXPECTED WHICH COULD RESULT IN LOCALIZED FLASH
FLOODING WITH URBANIZED AREAS AND REGIONS OF POOR DRAINAGE BEING
THE MOST VULNERABLE. WITH PRECIPITABLE WATER VALUES CLOSE TO 2
INCHES ACROSS THIS PORTION OF FLORIDA...AND EASTERLY FLOW OF 20 TO
25 KNOTS LARGELY ALIGNED PERPENDICULAR TO THE COASTLINE WHICH
MAXIMIZES CONVERGENCE COMBINED WITH SUBTLE CYCLONIC ROTATIONS
EVIDENT ON SATELLITE IMAGERY...THE ENVIRONMENT SHOULD BE ABLE TO
SUPPORT AND SUSTAIN UPWARDS OF 3 INCH PER HOUR RATES WITHIN ANY
SLOW MOVING AXIS OF RAINFALL. REFER TO MESOSCALE CONVECTIVE
DISCUSSION 1155 FOR ADDITIONAL DETAILS.
ACROSS PORTIONS OF THE SIERRA AND ADJACENT AREAS...TRAINING AND
REPEATING OF SHOWERS AND THUNDERSTORMS THIS EVENING MAY RESULT IN
LOCALIZED FLASH FLOODING DUE TO HOURLY RAINFALL RATES OF 0.5 TO
1.0 INCHES THAT COULD RESULT IN RAINFALL TOTALS OF 1 TO 2 INCHES.
EVEN THOUGH INSTABILITY IS MODEST...THE ENVIRONMENT IS
CHARACTERIZED BY PRECIPITABLE WATER VALUES OF 1.0 TO 1.4 INCHES (ON
THE ORDER OF +2 TO +4 STANDARDIZED ANOMALIES ABOVE CLIMATOLOGY FOR
EARLY OCTOBER) WHICH AT LEAST SUGGESTS LOCALLY INTENSE BUT BRIEF
DOWNPOURS COULD BE SUPPORTED. HIGHER RAINFALL INTENSITIES FALLING
ON SENSITIVE BURN SCARS OR URBAN AREAS WOULD BE MOST AT RISK FOR
LOCALIZED FLASH FLOODING INTO THE LATE EVENING.
BANN
DAY 2
VALID 12Z FRI OCT 03 2025 - 12Z SAT OCT 04 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE EAST-
CENTRAL FLORIDA COAST...
..EASTERN FLORIDA
20Z UPDATE: IN COORDINATION WITH THE MELBOURNE WFO, A SLGT RISK WAS
ADDED TO THE EAST-CENTRAL FLORIDA COAST SOUTH OF MELBOURNE. A
REMNANT MOISTURE FLUX TIED TO THE TRAILING LOW-LEVEL SHEAR AXIS
FROM IMELDA WILL SLOWLY PROPAGATE WESTWARD OUT OF THE BAHAMAS WITH
EMBEDDED MID-LEVEL VORTICITY TRYING TO DEVELOP INTO A MORE
CONCENTRIC CIRCULATION AS WE STEP INTO SATURDAY AM. THE PATTERN IS
A ONGOING EVOLUTION THAT BEGINS IN D1 AND JUST MOVES FORWARD IN
TIME WITH FRICTIONAL CONVERGENCE REGIME ALIGNED ALONG THE EASTERN
FL COAST, MAINLY IN LINE WITH A SURFACE TROUGH FORECAST PARALLEL TO
THE COASTAL PLAIN FOR THE FORESEEABLE FUTURE. SUFFICIENT LOW-LEVEL
BUOYANCY AIDED BY A THIN AXIS OF 1500-2000 J/KG OF MUCAPE ALONG THE
COAST WITH PWATS BETWEEN 1.8-2.2" SITUATED WITHIN THE SAME ZONE
SHOULD ALLOW FOR A HEIGHTENED THREAT OF LOCALLY HEAVY RAINFALL
WITHIN THE EAST-CENTRAL FL COASTAL PLAIN, NOTED BY SEVERAL CAMS AND
ENSEMBLE MEMBERS OF BOTH THE GEFS/ECENS. CONSIDERING THE HIGH
NEIGHBORHOOD PROBS FOR >5" (45-80%) FOCUSED NEAR AND JUST SOUTH OF
THE SPACE COAST, A SLGT RISK WAS ADDED FOR THE ELEVATED THREAT OF
FLASH FLOODING WITHIN THE URBAN ZONES THAT ALIGN THE IMMEDIATE
COAST TO JUST INLAND AROUND THE I-95 CORRIDOR. SOME ADJUSTMENTS IN
FUTURE UPDATES ARE PLAUSIBLE PENDING NEAR TERM CONVECTIVE
EVOLUTIONS, SO THIS IS A PERIOD TO MONITOR CLOSELY AS WE MOVE INTO
TOMORROW MORNING AND BEYOND.
..GREAT BASIN
20Z UPDATE: PREVIOUS FORECAST REMAINS STEADFAST WITH ONLY MINOR
CHANGES MADE TO THE MRGL RISK FORECAST ACROSS THE GREAT BASIN INTO
PORTIONS OF THE INTERIOR NORTHWEST. HEAVIEST PRECIP AXIS WILL BE
FOCUSED OVER CENTRAL NV INTO SOUTHERN ID AS THE UPPER TROUGH BEGINS
TO CLOSE OFF AS IT MIGRATES INLAND FROM THE PACIFIC LEADING TO
ENHANCED LARGE SCALE FORCING AND STEEPER LAPSE RATES FRIDAY
AFTERNOON AND EVENING IN THESE LOCATIONS. ANTICIPATING RATES TO
REMAIN <1"/HR FOR THE THREAT, HOWEVER SOME OF THESE LOCATIONS ARE
SUSCEPTIBLE TO EVEN 0.5"/HR RATES DUE TO HIGH RUN AND COMPLEX
TOPOGRAPHY THAT PROMOTES FUNNELING. AS A RESULT, THERE WASN'T MUCH
OF A REASON TO DEVIATE FROM THE LAST FORECAST ISSUANCE, SO ONLY
MINOR ADJUSTMENTS BASED ON UPDATED PROBS AND MEAN QPF DISTRIBUTION
WERE GENERATED IN THIS FORECAST CYCLE.
KLEEBAUER
..PREVIOUS DISCUSSION..
THE UPPER TROUGH PROPAGATES THROUGH THE GREAT BASIN AND BEGINS
LIFTING NORTH ON FRIDAY. THE EXCESSIVE RAINFALL THREAT BLEEDS INTO
FRIDAY FROM THURSDAY AS THUNDERSTORMS WEAKEN AND SPREAD FROM THE
GREAT BASIN INTO THE NORTHERN ROCKIES BY FRIDAY AFTERNOON. INSTABILITY
AND MOISTURE WILL BE RELATIVELY MODEST (100-200 J/KG MUCAPE)
(0.5-0.9"). ENSEMBLE EXCEEDANCE PROBABILITIES OF 1" ARE BETWEEN
10-20% OVER NORTHERN NEVADA WITH 2 DAY TOTALS POTENTIALLY ECLIPSING
2" IN SOME PLACES.
KEBEDE
DAY 3
VALID 12Z SAT OCT 04 2025 - 12Z SUN OCT 05 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE FLORIDA
SPACE COAST...
..EASTERN FLORIDA
20Z UPDATE: SURFACE EVOLUTION OF A WEAK SURFACE LOW OFF THE
EASTERN FL COAST WILL BE KEY IN DETERMINING THE EXTENT OF THE HEAVY
RAINFALL PERSISTENCE IN-OF THE FL COAST BY SATURDAY. AS OF NOW,
THE ENSEMBLE MEANS SUGGEST A WEAK SURFACE REFLECTION WILL FORM AND
MIGRATE SLOWLY INLAND OF THE PENINSULA BY SATURDAY AFTERNOON
LEADING TO A LARGER AREA OF THE FL COAST BEING SUBJECT TO ENHANCED
CONVERGENCE AND NORTHERN PUSH OF ELEVATED PWATS/INSTABILITY CAPABLE
OF FLASH FLOOD PROSPECTS. ENSEMBLE MEANS ARE MORE GENEROUS THAN
MOST DETERMINISTIC, HOWEVER THE THE SCHEME IS CERTAINLY FAVORABLE
FOR THE THREAT OF A REPEATED HEAVY RAIN SCENARIO IN-OF THE FL SPACE
COAST. IN COORDINATION WITH THE MELBOURNE WFO, ANOTHER SLGT RISK
WAS ADDED FOR MUCH OF THE CWA AS ENSEMBLE MEAN QPF OF >2" ALIGNS
BEST WITHIN THE ZONE THAT EXTENDS FROM DAYTONA BEACH DOWN TO PORT
ST LUCIE. IF THE D2 MATERIALIZES, THIS WILL END UP BEING A CASE
WHERE WET ANTECEDENT CONDITIONS WOULD EXACERBATE THE POTENTIAL
LEADING TO A GREATER CASE FOR SCATTERED FLASH FLOOD SIGNALS AS THE
PATTERN EVOLVES. WITH A BETTER LOW-LEVEL CONVERGENCE REGIME
GENERATING FROM THE SURFACE REFLECTION NEARBY, THE CHANCE FOR
HEAVIER PRECIP EXPANDING NORTH OF THE PREVIOUS PERIOD WOULD BE BE
HIGHER, THUS THE SLGT RISK HAVING A LARGER AREAL FOOTPRINT COMPARED
TO THE PREVIOUS D2. THIS REMAINS A PERIOD TO WATCH AS SMALL SHIFTS
IN THE SYNOPTIC SCHEME COULD SHIFT HEAVY RAIN PROXY AND SUBSEQUENT
MAGNITUDES.
..CENTRAL GULF COAST
20Z UPDATE: THIS SETUP REMAINS ON THE LOWER END OF THE MRGL RISK
THRESHOLD DUE TO THE DIFFERENCES IN PLACEMENT OF THE HEAVIEST
PRECIP ALIGNED WITH THE COASTAL CONVERGENCE REGIME FORMULATING OVER
THE NORTHERN GULF WATERS. THE LATITUDINAL PUSH OF THE CONVERGENT
AXIS WILL LIKELY DICTATE WHERE THE RISK IS EVEN NECESSARY AS THE
SOUTHERN PARISHES ARE MORE THAN CAPABLE TO ABSORB THE HEAVY RAIN
PROSPECTS PROMOTED BY SOME GUIDANCE. HOWEVER, THE URBAN CORRIDOR OF
NEW ORLEANS AND NEARBY SUBURBS ARE MORE SUSCEPTIBLE TO FLASH FLOOD
PROSPECTS AND WERE CLOSE ENOUGH TO THE HIGHEST MEAN QPF FORECAST
THAT THE MAIN SHIFT WAS TO INCLUDE THE METRO AND SHRINK THE OVERALL
RISK FOOTPRINT TO ALIGN WITH AREAS THAT WOULD SEE THE HEAVIEST
PRECIP POTENTIAL AND HAVE THE ABILITY TO ENTICE FLASH FLOOD
PROSPECTS.
KLEEBAUER
..PREVIOUS DISCUSSION..
MID- LEVEL VORTICITY SWIRLING OVER THE CENTRAL GULF
COAST WILL GENERATE INSTABILITY AND PULL AN INCREASING AMOUNT OF
GULF MOISTURE INTO THE REGION ON SATURDAY. CONVECTION SHOULD FIRE
ALONG A COASTAL CONVERGENCE ZONE THAT DEVELOPS AND DIURNAL HEATING
SHOULD ENHANCE AFTERNOON/EVENING STORMS ALONG THAT BOUNDARY. PWATS
WILL LIKELY BE OVER 2" WITH MUCAPE BETWEEN 500-750 J/KG. ENSEMBLE
EXCEEDANCE PROBABILITIES OF 2" ARE BETWEEN 15-30% FOR MUCH OF
SOUTHEAST LOUISIANA.
KEBEDE
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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