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FOUS30 KWBC 021603
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1203 PM EDT MON JUN 2 2025
DAY 1
VALID 16Z MON JUN 02 2025 - 12Z TUE JUN 03 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL PLAINS AS WELL AS THE SOUTHEAST FLORIDA PENINSULA...
..FOUR CORNERS THROUGH THE CENTRAL PLAINS
THE CAMS HAVE SHIFTED JUST A BIT NORTH/EAST TODAY WITH THE AXIS OF
HEAVIEST RAIN, OWING TO SUBTLE EVOLUTION CHANGES IN THE UPPER
PATTERN. THE COMBINATION OF ASCENT THROUGH HEIGHT FALLS,
CONVERGENCE ALONG THE SOUTHEAST ADVANCING FRONT, AND INCREASED
ASCENT IN THE VICINITY OF A DEVELOPING LOW PRESSURE WILL HELP FOCUS
CONVECTION WITH HEAVY RAINFALL INTO FAVORABLE THERMODYNAMICS.
THE HIGH-RES ENSEMBLE CAMPS (BOTH 12Z HREF AND 06Z REFS) ARE BOTH
STILL QUITE AGGRESSIVE WITH SUGGESTING MORE THAN 3 INCHES OF RAIN
ACROSS PORTIONS OF NEBRASKA AND INTO IA/MN/SD, AS FAR NORTH AS THE
COTEAU DES PRAIRIES. THE GREATEST RISK FOR EXCESSIVE RAINFALL
APPEARS TO BE ACROSS NEBRASKA, STILL, HOWEVER, AS CONVECTION ALONG
THE COLD FRONT INITIATES AND THEN BUILDS SW INTO THE GREATER
THERMODYNAMICS AS THE LOW EVOLVES, LEADING TO ENHANCED ISENTROPIC
ASCENT INTO THE BOUNDARY. FORTUNATELY, THE AREA OF GREATEST
EXCEEDANCE PROBABILITIES (50-80% CHANCE OF 3+ INCHES FROM THE HREF
AND REFS) OVERLAPS THE SANDHILLS WHICH ARE NOT A FAVORABLE FLASH
FLOOD LOCATION, OR OTHERWISE THIS EVENT COULD NECESSITATE A
TARGETED UPGRADE. STILL, WITH LOCALLY AS MUCH AS 5" OF RAIN
POSSIBLE THANKS TO SLOW MOVING/BACKBUILDING RAIN RATES OF 1-2"/HR,
AT LEAST SCATTERED INSTANCES OF FLASH FLOODING ARE EXPECTED, AND
THE SLGT RISK WAS MAINTAINED WITH ONLY MODEST COSMETIC
ADJUSTMENTS.
FARTHER SOUTHWEST, THE EJECTING UPPER LOW ADVANCING INTO A REGION
OF ELEVATED INSTABILITY AND EXTREMELY ANOMALOUS PWS (NAEFS PWS THE
MAXIMUMS IN THE 06Z CFSR DATABASE) WILL PROMOTE HEAVY RAIN
PRODUCING CONVECTION OVER THE FOUR CORNERS, ESPECIALLY DURING PEAK
HEATING. STORM MOTIONS WILL BE WEAK IN THIS AREA BENEATH THE UPPER
LOW, SO AS RAIN RATES WHICH MAY REACH 1"/HR (10-20% CHANCE) LEADING
TO 15-MIN RAINFALL THAT COULD REACH 0.25-0.5 INCHES. SHOULD ANY OF
THESE CELLS, WHICH COULD BE WIDESPREAD, MOVE ACROSS SENSITIVE
TERRAIN FEATURES LIKE SLOT CANYONS, INSTANCES OF FLASH FLOODING
COULD RESULT, AND THE MRGL RISK HAS BEEN MAINTAINED.
ADDITIONALLY, A WAVE OF LOW PRESSURE DEVELOPING IN THE LEE OF THE
SOUTHERN ROCKIES WILL LIKELY PUSH ADDITIONAL MODERATE TO HEAVY
RAINFALL ACROSS EASTERN CO LATE TONIGHT, AND WHILE THIS ROUND WILL
MOST LIKELY BE LESS INTENSE DUE TO WEAKER INSTABILITY, LOCALIZED
ADDITIONAL FLASH FLOODING IS POSSIBLE IF THE RAIN OCCURS ATOP OF
PRIMED SOILS FROM EARLIER CONVECTION.
..WEST TEXAS INTO TEXAS PANHANDLE AND WESTERN OK
THE SURFACE TROUGH/DRY LINE WILL FOCUS CONVECTIVE DEVELOPMENT THIS
AFTN/EVE AS DIURNAL HEATING PUSHES INSTABILITY TO 1000-3000 J/KG.
THIS ROBUST CAPE WILL WORK IN TANDEM WITH PWS EXCEEDING 1.5" AS SW
RETURN FLOW REACHES 30+ KTS, TO PRODUCE FAVORABLE THERMODYNAMICS
FOR HEAVY RAIN CONTAINING THUNDERSTORMS. THE GUIDANCE CONTINUES TO
VARY WIDELY WITH BOTH THE TIMING AND SPATIAL COVERAGE OF
THUNDERSTORMS TODAY, BUT LOW-LEVEL CONVERGENCE MOVING INTO THE
THERMODYNAMICS SHOULD SUPPORT AT LEAST SCATTERED CONVECTION ALONG
THIS BOUNDARY AS IT PUSHES EAST INTO TONIGHT. WHILE UNCERTAINTY IS
LOW AS FAR AS COVERAGE, IT IS HIGH THAT AT LEAST A FEW STORMS WILL
FIRE ALONG THIS BOUNDARY, AND THESE WILL RAPIDLY INTENSIFY WITHIN
THIS ENVIRONMENT. STORM MOTIONS OF GENERALLY 10-15 KTS TO THE WSW
WILL BE ALIGNED STRONGLY RIGHT OF THE CORFIDI VECTORS TO SUGGEST AT
LEAST SOME TRAINING IS POSSIBLE AS STORMS RE-DEVELOP INTO THE MORE
ROBUST INSTABILITY BEFORE TRACKING ENE. ADDITIONALLY, INCREASING
BULK SHEAR TO 25-30 KTS THIS EVENING MAY HELP ORGANIZE STORMS INTO
CLUSTERS, AND THE HIGH-RES INDICATES THE GREATEST CHANCE FOR AN MCS
TYPE OF EVENT WILL BE INTO WESTERN OK TONIGHT. ALTHOUGH SOME PARTS
OF THIS REGION HAVE MORE VULNERABLE SOILS DUE TO RECENT HEAVY
RAINFALL, THE GENERALLY SCATTERED NATURE OF CONVECTION ALONG WITH
UNCERTAINTY IN PLACEMENT SUGGESTS THE MRGL RISK REMAINS ACCURATE,
AND THIS WAS ONLY ADJUSTED SLIGHTLY FOR NEW GUIDANCE.
..SOUTH FLORIDA AND THE FLORIDA KEYS
NEAR RECORD PWS ACROSS SOUTHERN FLORIDA WILL PRODUCE AN ENVIRONMENT
FAVORABLE FOR EXCESSIVE RAINFALL TODAY. PWS ARE PROGGED TO REACH
ABOVE 2.2 INCHES, WHICH WOULD BE A DAILY RECORD FOR MFL ACCORDING
TO THE SPC SOUNDING CLIMATOLOGY. THIS MOISTURE WILL COMBINE WITH
MUCAPE OF 2000-3000 J/KG TO PROVIDE EXTREME THERMODYNAMICS TO
SUPPORT INTENSE RAINFALL RATES IN ANY THUNDERSTORMS, WHICH ARE
EXPECTED TO BE WIDESPREAD TODAY. THE PRIMARY MECHANISMS FOR ASCENT
WILL BE A WEAKENING FRONT STALLED ACROSS THE SOUTHERN PENINSULA, AS
WELL AS A POTENT SHORTWAVE MOVING ACROSS THE GULF AND TOWARDS THE
AREA, WITH SUBTLE DIFFLUENCE IN THE TAIL OF A JET STREAK OVER THE
ATLANTIC ADDITIONALLY CONTRIBUTING LIFT. THIS ALL SUGGESTS
WIDESPREAD CONVECTION THIS AFTN/EVE, WHICH IS SUPPORTED BY THE HIGH
RES CAMS. WITHIN THESE STORMS, RAINFALL RATES OF 2-3"/HR OR MORE
ARE LIKELY (40-60% CHANCE OF EXCEEDING 2"/HR ACCORDING TO BOTH HREF
AND REFS), WHICH THROUGH TRAINING OR REPEATED ROUNDS COULD PRODUCE
3-6" OF RAINFALL, WITH LOCAL AMOUNTS POTENTIALLY APPROACHING 8" AS
REFLECTED BY THE HREF PROBABILITIES. ANY AMOUNTS ABOVE 5" WOULD
LIKELY BE WHERE MULTIPLE ROUNDS OCCUR, BUT ALSO WHERE STORMS SLOW
OR MOVE CHAOTICALLY DUE TO BOUNDARY INTERACTIONS AND STORM MERGERS.
WHILE THIS PART OF FLORIDA TYPICALLY TAKES A LOT OF RAIN TO FLOOD,
THIS SETUP DOES SUPPORT A MORE PRONOUNCED FLASH FLOOD RISK TODAY.
DESPITE FFGS THAT REMAIN AROUND 4"/3HRS, EXCEEDANCE OF THIS
CRITERIA IS POSSIBLE, ESPECIALLY OVER URBAN AREAS THAT DO NOT DRAIN
AS EFFICIENTLY. THE FOCUS TODAY IS EXPECTED TO BE ACROSS THE
KEYS AND GOLD COAST OF FL, AND THIS IS WHERE THE SLGT RISK IS
FOCUSED AND HAS BEEN MODESTLY ADJUSTED FOR NEW GUIDANCE. HOWEVER,
THE MRGL RISK ENCOMPASSES MUCH OF THE SOUTHERN PENINSULA WHERE ANY
OF THESE SLOW MOVING HEAVY RAIN PRODUCING THUNDERSTORMS COULD
RESULT IN RUNOFF AND INSTANCES OF FLASH FLOODING.
WEISS
DAY 2
VALID 12Z TUE JUN 03 2025 - 12Z WED JUN 04 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PARTS OF THE
CENTRAL UNITED STATES AND OVER SOUTH FLORIDA...
..TEXAS TO THE GREAT LAKES
THE COLD FRONT PUSHING SOUTHEAST ACROSS THE CENTRAL CONUS TUESDAY
MAY BECOME MORE PROGRESSIVE AS THE BAJA LOW FROM SUNDAY GETS EVEN
MORE SHEARED INTO THE WESTERLIES, PRODUCING A MORE AMPLIFIED TROUGH
AXIS PIVOTING EAST INTO THE PLAINS. EMBEDDED WITHIN THIS FLOW,
MULTIPLE VORTICITY MAXIMA WILL ROTATE E/NE, LEADING TO ADDITIONALLY
ENHANCED LIFT, AIDED SIGNIFICANTLY THE LATTER HALF OF D3 BY
DIFFLUENCE WITHIN THE RRQ OF A POLEWARD ARCING JET STREAK
DOWNSTREAM OF THE TROUGH AXIS. THIS WILL RESULT IN EXPANSIVE AND
IMPRESSIVE DEEP LAYER ASCENT FROM THE SOUTHERN PLAINS THROUGH THE
GREAT LAKES, WITH RETURN FLOW OUT OF THE GULF ON 30-50 KTS AT 850MB
DRAWING IMPRESSIVE THERMODYNAMICS NORTHWARD INTO THE FRONT. THIS
SUGGESTS THAT CONVECTION WILL BE WIDESPREAD ACROSS THE AREA
TUESDAY, WHICH IS SUPPORTED BY BOTH THE AVAILABLE CAMS (WHICH ARE
LARGELY ABSENT FROM THE LATTER HALF OF D2 AT THIS JUNCTURE, THOUGH
THE RRFS AND CMC-REG OUTPUTS ARE IMPRESSIVE) AND THE GLOBAL MODELS
AND ENSEMBLES WITH RAINFALL RATES EXCEEDING 1"/HR LIKELY ANYWHERE
ALONG THE FRONT. THE GREATEST RISK FOR EXCESSIVE RAINFALL WILL BE
FROM NORTHERN TEXAS THROUGH SOUTHEASTERN IOWA AND WESTERN ILLINOIS
WHERE DEEPER WARM CLOUD DEPTHS WILL PRODUCE MORE EFFICIENT RAINFALL
RATES, WHICH WILL LIKELY TRAIN SW TO NE ALONG THE FRONT. THE SLGT
RISK WAS MAINTAINED FOR MUCH OF THE SAME AREA (AS MODELS ARE IN
VERY GOOD AGREEMENT ON THE PLACEMENT OF THE QPF AXIS) WHICH
CONTINUE TO MATCH THE HIGHEST PROBABILITIES FOR 2" AND 3"/24 HRS
FROM THE ECENS/GEFS. THE HIGHER-END PROBABILITIES OF THE SLGT
SPECTRUM EXIST FROM NORTHERN OK INTO SOUTHEASTERN KS AND CENTRAL
MO, WHERE AVAILABLE CAMS SUGGEST THE BEST TRAINING AXIS WILL OCCUR.
..SOUTH FLORIDA
A MEANDERING SHORTWAVE TROUGH POSITIONED OVER THE FLORIDA
PENINSULA WILL BE THE IMPETUS FOR ANOTHER ROUND OF SCATTERED TO
WIDESPREAD SHOWERS AND THUNDERSTORMS TUESDAY. WITH THERMODYNAMICS
REMAINING ROBUST ACROSS THE REGION (PWS 1.75 TO 2 INCHES AND MUCAPE
ABOVE 1000 J/KG), SLOW MOVING STORMS WILL AGAIN HAVE THE POTENTIAL
TO PRODUCE EXCESSIVE RAIN RATES ABOVE 2"/HR. WHILE THERE IS SOME
UNCERTAINTY INTO HOW MUCH CONVECTIVE DEBRIS FROM MONDAY COULD LIMIT
COVERAGE, THE GENERAL CONSENSUS AMONG THE VARIOUS ENSEMBLE CAMPS
IS FOR ANOTHER DAY OF HEAVY RAIN, ESPECIALLY ACROSS SOUTH FLORIDA,
WHERE MODELS REMAIN IN GOOD AGREEMENT SUGGESTING 3-5" LOCALIZED
TOTALS. THIS WILL FALL ATOP GROUND THAT WILL LIKELY BE SENSITIVE
FROM HEAVY RAIN ON D2, AND THE INHERITED SLGT AND MRGL RISKS ONLY
NEEDED MINOR ADJUSTMENTS (AS THE BEST AGREEMENT IN A HEAVY RAINFALL
AXIS REMAINS IN A SIMILAR POSITION AS D1, OVER FAR SOUTHERN
PORTIONS OF THE MAINLAND INTO THE UPPER KEYS).
CHURCHILL/WEISS
DAY 3
VALID 12Z WED JUN 04 2025 - 12Z THU JUN 05 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE INTERMOUNTAIN WEST INTO MUCH OF THE CENTRAL UNITED STATES, AS
WELL AS FOR SOME PORTIONS OF THE SOUTHEAST COAST...
..INTERMOUNTAIN WEST THROUGH CENTRAL UNITED STATES
A LARGE MRGL RISK WAS MAINTAINED AND EXPANDED A BIT ACROSS A VAST
PORTION OF CENTRAL CONUS, WHILE AN INHERITED SLGT RISK WAS REMOVED
OVER TX. WHILE SOME PRIOR MODEL RUNS SUGGESTED TX COULD SEE THE QPF
MAXIMA OF THE DAY, THAT APPEARS MUCH LESS LIKELY WITH THE RED RIVER
OF THE SOUTH REGION NOW CONVERSELY HAVING SOME OF THE LOWEST 1"
EXCEEDANCE PROBABILITIES (FROM 00Z ECENS/GEFS) OF THE WHOLE MRGL
REGION. THIS IS DUE TO BETTER SEPARATION BETWEEN THE TWO FEATURES
OF INTEREST, 1) ANOTHER MID- AND UPPER-LEVEL CLOSED LOW EJECTING
NORTHEASTWARD FROM AROUND SOUTHERN CA INTO THE INTERMOUNTAIN WEST
AND 2) THE AFOREMENTIONED COLD FRONT STALLING FROM THE SOUTHERN
PLAINS INTO THE MIDWEST, BUT WITH THE BULK OF THE FAVORABLE
FORCING FROM D2 LARGELY HAVING EXITED THE REGION (THOUGH A
SHORTWAVE PIVOTING THROUGH THE LARGER SCALE TROUGH IS OF INTEREST).
WHILE MOISTURE AND LIFT LOOKS SUFFICIENT ACROSS THE INTERMOUNTAIN
WEST FOR 0.5"+/HR RATES (WITH DOWNSCALED 00Z ECMWF AND GFS MODELS
DEPICTING LOCALIZED 1-2" TOTALS AMID PWATS IN THE VICINITY OF THE
90TH PERCENTILE), THE HIGHEST PROBABILITIES FOR 1" AND 2"
EXCEEDANCE EXIST FROM NORTHERN AR THROUGH SOUTHERN MI (WITH NOTABLY
HIGHER PROBABILITIES FROM THE 00Z ECENS OVER THE GEFS). WITH
CONSIDERABLE UNCERTAINTY AT THIS RANGE, OPTED TO MAINTAIN A BROAD
MRGL (THOUGH IF A SLGT IS EVENTUALLY REINTRODUCED, IT'S MORE LIKELY
TO BE LOCATED OVER THE MID MS VALLEY AND MIDWEST REGION).
..SOUTHEAST COAST
THE SHORTWAVE AND TROPICAL MOISTURE FROM PRIOR DAYS RAINFALL LOOKS
TO LIFT NORTHWARD BY D3, AS THE RIDGE AXIS OVER THE EASTERN CONUS
THAT STALLED THE FEATURE WEAKENS ENOUGH IN THE LOWER-LEVELS
(700-850 MB) TO ALLOW FOR NORTHWARD PROGRESS. THERE IS CONSIDERABLE
UNCERTAINTY REGARDING THE TIMING OF THE LIFT OF THIS FEATURE AND
ANY MEANINGFUL ORGANIZATION INTO A CLOSED LOW (MORE LIKELY TO
REMAIN A SURFACE TROUGH), BUT MODELS ARE IN OVERALL GOOD AGREEMENT
IN INDICATING THE POTENTIAL FOR SIGNIFICANT RAINFALL TOTALS JUST
OFFSHORE WITH THIS FEATURE. GIVEN THE PROXIMITY TO THE COASTLINE,
HAVE MAINTAINED (AND EXPANDED SOUTHWARD) AN INHERITED MRGL RISK.
CHURCHILL
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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