705
FOUS30 KWBC 231944
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
344 PM EDT SAT MAY 23 2026
DAY 1
VALID 16Z SAT MAY 23 2026 - 12Z SUN MAY 24 2026
...THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL FOR SOUTHEASTERN
TEXAS, SOUTHERN LOUISIANA, AND THE UPPER OHIO VALLEY...
16Z UPDATE...
..SOUTHERN PLAINS TO LOWER MISSISSIPPI VALLEY
GOES EAST SATELLITE PAINTS A CHAOTIC PICTURE WITH NUMEROUS CLUSTERS
OF THUNDERSTORMS THAT STRETCH FROM JUST EAST OF THE RIO GRANDE TO
AS FAR EAST AS SOUTHERN LOUISIANA. A CONVECTIVE COMPLEX EMERGING
OFF OF THE SIERRA MADRE IS TRACKING EAST INTO SOUTH TX WHERE RAP
MESOANALYSIS DEPICTS 3-HR MLCAPE CHANGES OF >600 J/KG. THERE IS
ALSO A NARROW THETA-E GRADIENT JUST NORTH OF CORPUS CHRISTI WITH SE
850MB INTERSECTING THE BOUNDARY. THIS ENVIRONMENT, ALONG WITH THE
APPROACHING 500MB VORT MAX PROVIDING SUPPORT ALOFT, WILL SUSTAIN
AND LIKELY IGNITE ADDITIONAL STORMS IN SOUTH TX TODAY WITH RAINFALL
RATES OF 2-2.5"/HR, PERHAPS EVEN 2" OF RAINFALL IN 30 MINUTES, IN
THE MOST INTENSE CELLS. THAT SAID, THESE STORMS ARE EMBEDDED WITHIN
A 20-30KT 850-300MB MEAN WIND FLOW, WHICH SHOULD KEEP STORMS
MOVING ALONG. THE BIGGEST THREAT FOR FLASH FLOODING LIKELY LIES
ALONG AND JUST SOUTH OF THE 850MB THETA-E AXIS WHERE INTERSECTING
LOW-LEVEL WINDS COULD TRIGGER STORMS IN ADVANCE OF THE MCS TRACKING
OVER THE RIO GRANDE. LATEST 12Z HREF SHOWS A NARROW AREA FROM JUST
SOUTHWEST OF HOUSTON WITH MODERATE-TO-HIGH CHANCES (50-70%) FOR
3HR QPF > 3HR FFG BETWEEN 18-21Z. STORMS MAY LINGER BETWEEN HOUSTON
AND GALVESTON ON EAST TO BEAUMONT THROUGH THIS AFTERNOON BEFORE
DISSIPATING THIS EVENING. WPC'S METWATCH DESK HAS ISSUED A COUPLE
OF MPDS (215 AND 216) HIGHLIGHTING THE ONGOING FLASH FLOOD THREAT
FOR SOUTHERN LA (215) AND SOUTHERN TX (216). PLEASE REFER TO WPC
METWATCH MPDS FOR THE LATEST INFORMATION AS THE DAY PROGRESSES.
GIVEN THE PROGRESSIVE NATURE OF THE STORMS, OPTED TO MAINTAIN WHAT
IS A "HIGH-END SLIGHT" FROM THE UPPER TX COAST TO SOUTHERN LA. THE
SLIGHT ALSO EXTENDS SOUTH TO JUST NORTH OF THE RIO GRANDE.
SCATTERED AREAS OF FLASH FLOODING ARE POSSIBLE TODAY WITH MORE
URBANIZED SETTING MOST VULNERABLE. LOCALIZED CASES OF SIGNIFICANT
FLASH FLOODING CAN OCCUR, PARTICULARLY IF BACK-BUILDING AND
TRAINING CELLS ALONG THE UPPER TX COAST ON EAST TO SOUTHERN LA
TRANSPIRE. RESIDENTS IN THESE AREAS SHOULD ENSURE THEY HAVE A
RELIABLE METHOD TO RECEIVE ANY FLASH FLOOD WARNINGS ISSUED TODAY
AND THIS EVENING.
FARTHER EAST, A 300MB DISTURBANCE WILL EJECT EAST OVER THE
ARKLATEX AT THE SAME TIME A SOUTHERLY IVT OUT OF THE WESTERN GULF
ADVECTS ANOMALOUS MOISTURE INTO THE SOUTHERN MS VALLEY THIS
AFTERNOON AND INTO TONIGHT. SUFFICIENT SHEAR COUPLED WITH MUCAPE
>2,000 J/KG WILL TRIGGER NUMEROUS THUNDERSTORMS FROM NORTHERN LA
AND THE ARKLATEX ON EAST THROUGH THE LOWER MS VALLEY AND EVEN AS
FAR NORTH AS THE OZARKS. STORMS MAY FLARE UP OVER AL AS WELL, WHERE
NASA SPORT-LIS 0-40CM ANOMALIES ARE >90%. FOR THESE REASONS, THE
MARGINAL RISK WAS EXTENDED TO COVER ALL OF MS/AL AND INTO THE TN
VALLEY.
..OHIO VALLEY
12Z SURFACE ANALYSIS SHOWS A CLASSING CAD SIGNATURE IN THE EAST
WITH A N-S ORIENTED STALLED FRONT FROM THE CUMBERLAND PLATEAU ON
NORTH TO THE OH RIVER. THE FRONT ORIENTED SW-NE FROM FROM THE LOWER
MS VALLEY TO THE LOWER OH VALLEY WILL SLOWLY ADVANCE EAST, BUT WILL
NOT ADVANCE EAST MUCH TOWARDS THE UPPER OH VALLEY TODAY. AS THE
PRIMARY LOW IN NORTHWEST OH MOVES NORTHEAST TOWARDS LAKE ERIE, THE
WARM SECTOR WILL ADVANCE NORTH INTO EASTERN OH AND WESTERN PA WITH
A NARROW TONGUE OF 500-1,000 J/KG OF MLCAPE ENCOMPASSING EASTERN
KY, SOUTHERN AND EASTERN OH, AND WESTERN WV. LATEST HRRR AND RAP
SOUNDINGS SHOW HIGHLY SATURATED SOUNDINGS (>85%) IN THE 1000-500MB
LAYER, WARM CLOUD LAYERS UP TO 12,000FT DEEP, AND UPSHEAR CORFIDI
VECTORS <10 KTS IN SOME CASES. CLOUD LAYER WINDS ARE UNIFORMLY OUT
OF THE SW, INTERSECTING THE LIFTING WARM FRONT IN EASTERN OH AND
WESTERN PA AND PARALLEL TO THE QUASI-STATIONARY FRONT TO THE WEST.
THIS SETUP IS RIPE FOR NOT ONLY THUNDERSTORMS CONTAINING EFFICIENT
WARM-RAIN PROCESSES, BUT ALSO FOR TRAINING AND BACK-BUILDING
CELLS.
FFGS REMAIN QUITE LOW WITH 1-HR FFGS <1" IN SOME AREAS, AND 3-HR
FFGS <1.5" ALONG AND JUST WEST OF THE OH RIVER. NASA SPORT-LIS ALSO
SHOWS >95% SOIL SATURATION PERCENTILES FOR MUCH OF THE REGION. WITH
THESE FACTORS, OPTED TO UPGRADE TO A SLIGHT RISK FROM NORTHEAST KY
ON NORTH AND EAST INTO THE UPPER OH VALLEY. SCATTERED INSTANCES OF
FLASH FLOODING ARE POSSIBLE, WITH LOCALLY SIGNIFICANT FLASH
FLOODING NOT OUT OT THE REALM OF POSSIBILITY. THIS IS BACKED BY THE
LATEST 12Z HREF GUIDANCE THAT SHOW
..SOUTHEAST
FROM FLORIDA ON NORTH TO THE CAROLINAS, THE REGION LIES ON THE
WESTERN PERIPHERY OF A BERMUDA HIGH WHILE EMBEDDED 500MB
DISTURBANCES TRACK OVER THE REGION DUE TO BROAD LONGWAVE TROUGHING
TO THE WEST. A STALLED FRONT IN THE CAROLINAS, MARKING THE SOUTHERN
FRINGE OF THE CAD SIGNAL IN THE EAST, WILL ACT AS A TRIGGER FOR
ADDITIONAL STORMS TODAY THANKS TO SOUTHERLY 850MB FLOW INTERSECTING
THE FRONT. THE CAROLINAS AND INTO CENTRAL GA WILL SPORT AN IVT
>400 KG/M/S TODAY THAT WILL PROVIDE NO SHORTAGE OF ATMOSPHERIC
MOISTURE ALOFT. PWATS >1.75" ARE LIKELY (ABOVE THE 97.5
CLIMATOLOGICAL PERCENTILE) IN THE CAROLINAS AND MUCAPE UP TO
1,000 J/KG PROVIDES A FAVORABLE ENVIRONMENT FOR RAINFALL RATES UP
TO 1.5"/HR. FARTHER SOUTH INTO GA, WHERE INSTABILITY IS GREATER,
RAINFALL RATES ECLIPSING 2"/HR ARE POSSIBLE THIS AFTERNOON AND
EVENING. SOME CAMS DO SHOW THE POTENTIAL FOR STRONG THUNDERSTORMS
WITH TORRENTIAL RAINFALL RATES POTENTIALLY SNEAKING INTO THE
ATLANTA METRO AREA THIS AFTERNOON. THE "PEACH STATE" IS CONSUMED IN
SEVERE DROUGHT CONDITIONS, SO MUCH OF THIS RAINFALL WILL BE
WELCOMED. THAT SAID, EXCESSIVE RAINFALL RATES REFERENCED ABOVE IN
URBANIZED LOCATIONS OR AREAS THAT DRAIN POORLY COULD STILL SEE
CASES OF FLASH FLOODING OCCUR. THE MARGINAL RISK WAS EXPANDED FOR
TO ENCOMPASS MOST OF THE STATE (GA COAST LINE THE LONE EXCEPTION).
FARTHER SOUTH, STRONG SURFACE BASED HEATING IS ONGOING
FROM TAMPA BAY ON NORTH AND EAST TOWARDS ORLANDO AND THE
NORTHERN FL ATLANTIC COAST. 12Z CAMS SHOW GOOD AGREEMENT ON A
CLUSTER OF POTENT THUNDERSTORMS FLARING UP WITH RAINFALL RATES
BETWEEN 2-3"/HR POSSIBLE. PWS IN FL ARE ANOMALOUS AS WELL FOR LATE
MAY WITH >2.0" PWS LIKELY AND PLENTY OF INSTABILITY (>1,000 J/KG
MLCAPE). WHILE MUCH OF FL CAN CERTAINLY USE THE RAIN, MANY CAMS
SHOW THESE STORMS FLARING UP OVER SOME OF THE SUNSHINE STATE'S MAIN
THOROUGHFARES (I-10, I-75, I-4 MOST NOTABLY). STORMS SHOULD
SUBSIDE LATER TONIGHT, BUT TORRENTIAL DOWNPOURS IN URBANIZED AREAS
COULD POSE A FLASH FLOOD THREAT THIS AFTERNOON AND EVENING. DUE TO
THESE FACTORS, THE MARGINAL RISK WAS EXPANDED INTO NORTHERN AND
CENTRAL FL TODAY.
MULLINAX
DAY 2
VALID 12Z SUN MAY 24 2026 - 12Z MON MAY 25 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE UPPER
TEXAS COAST, SOUTHERN LOUISIANA, AND SOUTHERN MISSISSIPPI...
20Z UPDATE...
THE SLIGHT RISK WAS ADJUSTED TO MIMIC THE LATEST WPC QPF WHICH
SHOWED INCREASED PRECIPITATION OVER SOUTHEAST LA AND SOUTHERN MS.
THIS IS DUE TO THE GROWING SENTIMENT, ACROSS VARIOUS GUIDANCE
MEMBERS, THAT THE CLOSED 700MB LOW OVER THE UPPER TX COAST WILL
REMAIN SLOW MOVING AND MAINTAIN A PROLONGED FETCH OF ANOMALOUS
MOISTURE. ECMWF SATS SHOWS A CONTINUOUS >400 KG/M/S IVT FETCH
(ABOVE THE 90TH CLIMATOLOGICAL PERCENTILE) OVER SOUTHERN LA FOR
MUCH OF THE DAY. THE LOWER MS VALLEY ALSO RESIDES DOWNWIND OF A
NEGATIVELY-TILTED 200-500MB TROUGH AXIS THAT ENHANCES VERTICAL
ASCENT ATOP THE UPPER TROPOSPHERE. INSTABILITY WILL BE THE BIGGEST
QUESTION MARK IN SOUTH-CENTRAL LA, BUT SOILS HAVE GROWN
INCREASINGLY SATURATED THANKS TO RAINFALL IN RECENT DAYS (AND
DURING THE DAY SATURDAY, TOO). THE BEST INSTABILITY SHOULD RESIDE
JUST EAST OF NOLA ON NORTH INTO SOUTHERN MS WHERE MUCAPE IN EXCESS
OF 2,000 J/KG IS EXPECTED. RAINFALL RATES IN EXCESS OF 2"/HR ARE
LIKELY IN THE HEAVIER THUNDERSTORMS WHEN ACCOUNTING FOR >2" PWATS.
FOR THESE REASONS, THE SLIGHT WAS EXPANDED MORE INTO SOUTHEAST LA
AND SOUTHERN MS.
ELSEWHERE, THERE WAS A CHANGE IN GUIDANCE WITH A MORE EXPANSIVE
AREA OF SHOWERS AND STORMS TO THE WEST. THE FRONTAL BOUNDARY
APPROACHING FROM THE MIDWEST IS A LITTLE SLOWER, ALLOWING FOR
SCATTERED STORMS TO FORM OVER THE EASTERN CORN BELT ON SOUTH TO
WESTERN TN. WITH SUFFICIENT INSTABILITY PRESENT AND THESE AREAS
STILL DEALING WITH OVERLY SATURATED SOILS, DECIDED TO EXPAND THE
MARGINAL RISK WESTWARD. IN ADDITION, THE MARGINAL RISK WAS
EXPANDED EASTWARD TO COVER EASTERN NC AND SOUTHEAST VA. THE
STATIONARY FRONT IN THE SOUTHEAST LIFTS NORTH AS A WARM FRONT ON
SUNDAY, PUTTING THE SOUTHEAST VA TIDEWATER REGION AND EASTERN NC
SQUARELY IN THE WARM SECTOR. PWS APPROACHING 2" AND MLCAPE BETWEEN
500-1,000 J/KG WILL BE MORE THAN ENOUGH TO SUPPORT RAINFALL RATES
OF 2-3"/HR, ALONG WITH WARM CLOUD LAYERS AS DEEP AS 12,000FT. THERE
REMAINS UNCERTAINTY IN THE PLACEMENT OF THE HEAVIEST RAINFALL, BUT
GIVEN THESE RATES AND SOME URBANIZED AREAS PRESENT, THE MARGINAL
RISK WAS EXPANDED TO THESE REGIONS.
MULLINAX
---PREVIOUS DISCUSSION---
A SLOW MOVING UPPER TROF EXPECTED TO AMPLIFY SOMEWHAT DAY 2 AS IT
PUSHES FROM EASTERN TEXAS INTO THE LOWER MS VALLEY. THIS WILL
LIKELY HELP FIRE ANOTHER ROUND OF CONVECTION IN THE VICINITY OF THE
UPPER TX COAST, EASTWARD INTO SOUTHERN LA. AT THE MOMENT, IT
APPEARS THE BEST INSTABILITY AHEAD OF THIS NEXT CLOSED LOW WILL BE
SUPPRESSED SOUTHWARD INTO THE NORTHERN GULF IN THE WAKE OF THE
ACTIVE DAY 1 CONVECTION. THIS MAY SUPPORT THE HEAVIEST RAINS BEING
SHUNTED SOUTHWARD AND OFF THE COAST DAY 2, AS SUGGESTED BY THE RRFS
MEAN AND THE FV3LAM. THERE IS STILL A LOT OF MODEL SPREAD, BUT WPC
QPF HAS TRENDED SOUTH, WITH THE HEAVIEST OFFSHORE. SUBSEQUENTLY,
THE PREVIOUS SLIGHT RISK AREA HAS BEEN TRIMMED ON THE NORTH END,
CONFINED TO THE FAR UPPER TX COAST INTO SOUTHWEST LA. THERE MAY BE
OVERLAP OF THE DAY 1 AND DAY 2 HEAVY RAIN AREAS OVER THE UPPER TX
COAST INTO SOUTHWEST LA. HOWEVER, AT THE MOMENT, THE RISK LEVEL WAS
MAINTAINED AS SLIGHT AS THERE IS STILL MODEL SPREAD WITH THE DAY 2
HEAVIEST QPF AXIS.
NO SIGNIFICANT CHANGES MADE TO THE PREVIOUS BROAD MARGINAL RISK
AREA EXTENDING NORTHEASTWARD FROM THE CENTRAL GULF COAST, ACROSS
THE SOUTH AND INTO THE SOUTHERN TO CENTRAL APPALACHIANS. SIMILAR
TO THE DAY 1 PERIOD, THERE WILL CONTINUE TO BE AN AXIS OF MUCH
ABOVE AVERAGE PW VALUES STRETCHING ACROSS THESE AREAS, WITH
EMBEDDED SHORTWAVES IN THE BROAD SOUTHWESTERLY MID TO UPPER LEVEL
FLOW, SUPPORTING WIDESPREAD SCATTERED CONVECTION, LOCALLY HEAVY
RAINS AND ISOLATED RUNOFF ISSUES.
ORAVEC
DAY 3
VALID 12Z MON MAY 25 2026 - 12Z TUE MAY 26 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE CENTRAL
GULF COAST, TENNESSEE VALLEY, AND SOUTHERN APPALACHIANS...
THE INHERITED SLIGHT RISK AREA IN THE SOUTHERN APPALACHIANS WAS
EXPENDED SOUTH AND WEST ALL THE WAY TO THE CENTRAL GULF COAST. THE
CLOSED UPPER-LOW IN EAST TX THAT SLOWLY DRIFTS OVER THE ARKLATEX
MONDAY NIGHT CONTINUES IT SOUTHERLY ONSLAUGHT OF ANOMALOUS GULF
MOISTURE. PWS ABOVE 2.0" ARE LIKELY THROUGHOUT THE DEEP SOUTH,
MUCAPE >1,000 J/KG, AND SOILS WILL ONLY CONTINUE TO GROW MORE
SATURATED WITH SUNDAY'S RAINFALL. RAINFALL TOTALS BETWEEN 1-3" ARE
ANTICIPATED WITHIN THE SLIGHT RISK AREA, HOWEVER THE EXACT AXIS OF
HEAVIEST RAINFALL AT THIS RANGE IS STILL IN FLUX. ADDITIONAL
CHANGES TO THE PLACEMENT OF THE SLIGHT RISK AREA ARE STILL LIKELY
TO COME, BUT THE METEOROLOGICAL SETUP IS PRIMED FOR MORE SCATTERED
INSTANCES OF FLASH FLOODING FROM THE CENTRAL GULF COAST TO THE
SOUTHERN APPALACHIANS ON MONDAY.
FARTHER EAST, ADDITIONAL HEAVY RAINFALL IS POSSIBLE OVER SOUTHERN
VA AND NORTHERN NC. WITH THESE AREAS SPORTING MORE SENSITIVE SOILS
IN WAKE OF SUNDAY'S RAINFALL, THE ANOMALOUS PWS AND LINGERING
INSTABILITY ALOFT MAY LEAD TO ADDITIONAL ISOLATED CASES OF FLASH
FLOODING ON MONDAY.
MULLINAX
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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