532
FOUS30 KWBC 021544
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1144 AM EDT THU OCT 2 2025
DAY 1
VALID 16Z THU OCT 02 2025 - 12Z FRI OCT 03 2025
...THERE'S A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SIERRA, GREAT BASIN AND EASTERN FLORIDA...
16Z UPDATE: THE PREVIOUS FORECAST HAS NOT CHANGED MUCH IN THE
OVERALL SYNOPTIC AND MESOSCALE EXPECTATIONS OVER THE TWO RISK AREAS
OUTLINED.
ACROSS FL, LOCALLY HEAVY RAINFALL WITHIN THE CONFINES OF
A SURFACE TROUGH AXIS ALIGNED PARALLEL, JUST INLAND FROM THE
COASTAL PLAIN WILL BE THE THREAT THROUGH THE PERIOD WITH URBAN
FLASH FLOODING THE MOST LIKELY CASE OF ANY POTENTIAL. HIGHEST 5"
PROBS VIA 12Z HREF NEIGHBORHOOD OUTPUT ARE STILL IN THAT 40-90%
RANGE, HOWEVER THE HIGHEST PROBS ARE CENTERED BETWEEN MELBOURNE TO
WEST PALM BEACH WITH A CENTROID NEAR PORT ST LUCIE. THIS IS HI-RES
INDICATIONS OF WHERE THEY ANTICIPATE THE STRONGEST LOW-LEVEL
CONVERGENCE REGIME WITH RELEVANT MOISTURE FLUX SITUATED JUST OFF
THE ATLANTIC COAST AT SIMILAR LATITUDE TO THE ELEVATED PROBS.
CONSIDERING SOME ERROR IN CONVECTIVE PLACEMENT, IT'S STILL
REASONABLE TO CONSIDER AREAS FROM MIAMI UP TO DAYTONA WITHIN THE
PROXY FOR LOCALLY ENHANCED RAINFALL RATES WITH HOURLY RATES ~3"/HR
AT PEAK INTENSITY WHEN YOU FACTOR PWATS HOVERING BETWEEN 1.75-2"
AS OF THE 10/12Z RAOB SOUNDINGS FROM CAPE CANAVERAL. THIS SIGNAL
IN THE MEANS AND INDIVIDUAL DETERMINISTIC IS MORE THAN SUFFICIENT
FOR A MAINTENANCE OF THE MRGL RISK IN PLACE WITH ONLY A MINOR
NORTHWARD EXPANSION IN THE AREA TO COVER FOR THE CURRENT RADAR
TRENDS.
ACROSS THE WEST, THE SETUP REMAINS CONSISTENT AMONG ALL THE CAMS
AND GLOBAL DETERMINISTIC WITH A RELATIVE MAX SITUATED OVER THE
NORTHERN SIERRA ALONG AND NEAR I-80 WHERE MODEST INSTABILITY AND
SUFFICIENT LARGE SCALE ASCENT SHOULD INITIATE A PERIOD OF MODERATE
TO HEAVY RAIN FOR MULTIPLE HOURS THAT COULD ENHANCE A LOCALIZED
FLOOD PROSPECT. AS WE MOVE FURTHER INLAND INTO THE GREAT BASIN, THE
SETUP SHIFTS TO MORE SCATTERED/WIDESPREAD CONVECTIVE SCHEMES THAT
ARE BETTER SUITED FOR THOSE HIGHLY LOCALIZED FLASH FLOOD CONCERNS
WITHIN TOPOGRAPHY THAT HISTORICALLY FAVORS FLASHIER OUTPUT DUE TO
THE SOIL COMPOSITION AND PREVALENCE OF DRY WASHES AND ARROYOS
LITTERED OVER THE HIGH DESERT. THIS THREAT EXPANDS INTO THE SNAKE
RIVER BASIN OF ID AND ADJACENT ZONES LATER THIS EVENING. TOTALS
BETWEEN 1-2" (LOCALLY HIGHER IN THE NORTHERN SIERRA) WILL BE MOST
COMMON IN THE MRGL RISK IN PLACE FROM THE CENTRAL VALLEY OF
CALIFORNIA UP INTO SAWTOOTH AND SALMON RIVER RANGES OF IDAHO.
KLEEBAUER
..PREVIOUS DISCUSSIONS..
..SIERRA/GREAT BASIN
AN UPPER LOW WILL DIG INTO THE WEST COAST WHILE SENDING STREAMS OF
VORTICITY INTO THE SIERRA NEVADA, GREAT BASIN AND NORTHERN
ROCKIES. DIFFLUENCE WILL SPREAD ACROSS THE AFOREMENTIONED AREAS
THROUGHOUT THE DAY ON FRIDAY. AT THE SURFACE, A LOW PRESSURE SYSTEM
WILL PROPAGATE ACROSS THE INTERIOR WEST, WHILE ANOMALOUS MOISTURE
(3-4 STNDV PWATS) STREAMS IN BEHIND THE PRECEDING COLD FRONT.
SCATTERED TO ISOLATED THUNDERSTORMS MAY DEVELOP AND PRODUCE
ISOLATED INSTANCES OF EXCESSIVE RAINFALL AND FLASH FLOODING.
UPSLOPE ENHANCEMENT ACROSS THE SIERRA COULD PRODUCE HEAVIER
RAINFALL TOTALS THAN WHAT ARE CURRENTLY FORECAST. EAS PROBABILITIES
OF 24 HOUR QPF EXCEEDING 1 INCH ARE OVER 40% IN THE SIERRA AND
BETWEEN 15-40% IN THE GREAT BASIN. THEREFORE, BURN SCARS OVER
CENTRAL AND SOUTHERN IDAHO ARE AT RISK OF FLASH FLOODING TODAY.
..EASTERN FLORIDA
MOIST EASTERLY FLOW INTO A SURFACE FRONT ORIENTED NORTH-SOUTH WILL
PRODUCE SCATTERED CONVECTION ACROSS FLORIDA TODAY. THE SURFACE
BOUNDARY DRAPED ALONG THE EASTERN COAST WILL FOCUS PWATS OF AROUND
2" IN THAT AREA WHERE MUCAPE BETWEEN 500-1000 J/KG WILL ALSO LIKELY
PRODUCE HIGH RAIN RATES. NEIGHBORHOOD PROBABILITIES OF EXCEEDING
5" IN 24 HOURS ARE BETWEEN 40-90% FROM NEAR MIAMI METRO UP THROUGH
MELBOURNE AND ORLANDO.
KEBEDE
DAY 2
VALID 12Z FRI OCT 03 2025 - 12Z SAT OCT 04 2025
...THERE'S A MARGINAL RISK FOR PORTIONS OF THE GREAT BASIN AND
EASTERN FLORIDA...
..GREAT BASIN
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.
..EASTERN FLORIDA
MOISTURE ADVECTION INTO FLORIDA INCREASES ON FRIDAY AS A MID-LEVEL
CIRCULATION EMBEDDED WITHIN A BROADER UPPER RIDGE CONTINUES TO
DIRECT MOISTURE AND INSTABILITY INTO THE STATE'S EAST COAST.
ANOTHER INVERTED SURFACE TROUGH MAY DEVELOP ALONG THE STATE'S EAST
COAST AND FOCUS CONVECTION ALONG THE CONVERGENCE ZONE. ENSEMBLE
EXCEEDANCE PROBABILITIES OF 2" ARE BETWEEN 5-15% ALONG THE
IMMEDIATE COAST, WHILE FIRST GUESS FIELDS SUPPORT THE MARGINAL WITH
5% FLASH FLOOD PROBABILITIES.
KEBEDE
DAY 3
VALID 12Z SAT OCT 04 2025 - 12Z SUN OCT 05 2025
...THERE'S A MARGINAL RISK FOR PORTIONS OF SOUTHEAST LOUISIANA AND
EASTERN FLORIDA INTO FAR SOUTHEASTERN GEORGIA...
..CENTRAL GULF COAST
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.
..EASTERN FLORIDA/SOUTHEASTERN GEORGIA
TROPICAL MOISTURE ASSOCIATED WITH IMELDA WILL CONTINUE FLOWING INTO
FLORIDA DUE TO AND UPPER RIDGE OVER THE EAST COAST AND EMBEDDED
TROUGHING OVER FLORIDA AND THE GULF. A MODEST INSTABILITY PLUME
SHOULD FLOW UP THE FLORIDA PENINSULA INTO FAR SOUTHEASTERN GEORGIA
WHERE PWAT'S OF OVER 2" AND AN INVERTED SURFACE TROUGH COULD
COMBINE TO PRODUCE THUNDERSTORMS CAPABLE OF GENERATING 0.75-1"/HR
RAIN RATES. ENSEMBLE EXCEEDANCE PROBABILITIES OF 2" ARE BETWEEN
5-15% ALONG FLORIDA'S EAST COAST INTO SOUTHEASTERN GEORGIA.
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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