578
FOUS30 KWBC 061945
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
345 PM EDT WED MAY 6 2026
DAY 1
VALID 16Z WED MAY 06 2026 - 12Z THU MAY 07 2026
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
MISSISSIPPI AND ALABAMA...
..16Z UPDATE
...NORTHERN LOUISIANA, SOUTHERN MISSISSIPPI, AND CENTRAL/SOUTHERN
ALABAMA...
IN COORDINATION WITH JAN/JACKSON, MS AND BMX/BIRMINGHAM, AL
FORECAST OFFICES, A MODERATE RISK UPGRADE WAS INTRODUCED WITH THIS
UPDATE OVER A PORTION OF SOUTHERN MISSISSIPPI AND WEST-CENTRAL
ALABAMA.
CAMS GUIDANCE CONTINUES TO INCREASE THE POTENTIAL RAINFALL
EXPECTED OVER THE AREA LATE THIS AFTERNOON THROUGH MUCH OF THE
OVERNIGHT TONIGHT. A SLOW-MOVING COLD FRONT OVER THE MID-SOUTH IS
COLLIDING WITH ABUNDANT GULF MOISTURE, NOTABLE INSTABILITY AND
MOISTURE ADVECTION ACROSS PORTIONS OF THE SOUTH. CORFIDI VECTORS,
WHILE A BIT FAST FOR TRULY IDEAL TRAINING, ARE STILL ALIGNED
PARALLEL TO THE FRONTAL INTERFACE (WSW TO ENE) AT ABOUT 15 KT.
PWATS ARE EXPECTED TO INCREASE TO OVER 2 INCHES ACROSS THE MODERATE
RISK AREA AND SOUTHWEST INTO LOUISIANA. 850 MB ADVECTION AT 20-30
KTS FOR MUCH OF THE DAY WILL INCREASE TO 30-40 KTS ACROSS THE
MODERATE RISK AREA AFTER SUNSET TONIGHT WITH THE TYPICAL NOCTURNAL
STRENGTHENING OF THE LLJ. THE PERSISTENT LLJ ADVECTING DEEP
TROPICAL MOISTURE WILL HAVE NO PROBLEM SUPPORTING BACKBUILDING
CONVECTION EVEN INTO LOUISIANA, WHICH WILL THEN TRACK EAST ALONG
THE FRONT, FORMING A TRAINING PATTERN ACROSS SOUTHERN MISSISSIPPI
AND WESTERN ALABAMA. FINALLY, IN THE UPPER LEVELS, A STRONG
SHORTWAVE TROUGH WILL APPROACH FROM THE NORTH AND WEST LATE
TONIGHT. THIS WILL DRAG THE RRQ OF A 150 KT JET OVER THIS REGION,
WHICH WILL BOTH ENHANCE BROAD SCALE LIFT, AND SUPPORT CONVECTIVE
INITIATION TO THE NORTH AND WEST, WHICH WILL PROLONG THE RAINFALL
EVENT.
CAMS GUIDANCE IS IN GOOD AGREEMENT THAT CONVECTIVE INITIATION
ACROSS LOUISIANA AND MISSISSIPPI WILL BEGIN AROUND 19Z/2PM CDT THIS
AFTERNOON. BY THEN, WITH ABUNDANT MOISTURE WELL IN PLACE,
INSTABILITY WILL ALREADY BE ABOVE 3,000 J/KG ALONG AND SOUTH OF THE
FRONT. CELLS WILL QUICKLY ORGANIZE INTO CONVECTIVE CLUSTERS
ALIGNED ALONG THE FRONTAL INTERFACE. THERE IS A BIT MORE
UNCERTAINTY WITH HOW FAR NORTH THE TRAINING CELLS GET INTO PORTIONS
OF NORTH-CENTRAL ALABAMA. AN ENSEMBLE OF THE CAMS SUGGEST THAT
THERE WILL BE A MINIMUM OF RAINFALL IN AND AROUND THE BIRMINGHAM
AREA, SUGGESTING THAT THE NORTHERN BOUNDARY OF THE HEAVIEST RAIN
WILL LIKELY BE SOUTH OF THERE. THE CONVECTION ACROSS MISSISSIPPI
WILL TRACK EAST INTO WEST-CENTRAL ALABAMA, WHERE THE MODERATE RISK
CONTINUES. BY THIS POINT THE CELLS SHOULD BE FAIRLY WELL CONGEALED
AND MOVING AWAY FROM THE STRONGEST INSTABILITY AND MOISTURE
ADVECTION. HOWEVER, THE STORMS ACROSS ALABAMA WILL PERSIST FOR MUCH
LONGER INTO THE NIGHT. THUS, THE DURATION FACTOR OF THE HEAVY RAIN
WILL BE MORE OF A FACTOR CONTRIBUTING TO FLASH FLOODING TO THE
EAST, WHILE THE INTENSITY WILL BE THE GREATER FACTOR TO THE WEST.
RECENT TRENDS IN THE GUIDANCE ARE FOLLOWING A VERY COMMON PATTERN,
NAMELY TO SHIFT THE HEAVIEST RAINS SOUTH AND WEST WITH TIME, WHICH
FOLLOWS THAT THE STORMS TRACK TOWARDS WHERE THE ENVIRONMENT IS MOST
FAVORABLE...WHICH IS TOWARDS THE MOISTURE SOURCE, THE GULF. THUS,
CONCERN IS INCREASING FOR POTENTIALLY NEEDING EXTENSIONS OF THE
MODERATE TOWARDS THE SOUTH AND WEST LATER THIS AFTERNOON THROUGH
THE EVENING.
...NORTHEAST ALABAMA, NORTH GEORGIA, SOUTHEAST TENNESSEE, FAR
WESTERN NORTH CAROLINA, AND FAR WESTERN SOUTH CAROLINA...
A WEAKENING MCS OVER THIS REGION CURRENTLY IS EXPECTED TO GIVE WAY
TO ADDITIONAL CONVECTION FROM THE REMNANT STORMS CURRENTLY OVER
SOUTHWEST TENNESSEE AND FAR NORTHERN MISSISSIPPI, AS WELL AS
ADDITIONAL CONVECTION FROM DAY TIME HEATING IN THE SPACE IN BETWEEN
ALONG TENNESSEE'S SOUTHERN BORDER. THESE STORMS ARE ALSO SET UP IN
A TRAINING PATTERN. UNLIKE FURTHER SOUTH, HOWEVER, THE TOPOGRAPHY
OF THE SOUTHERN APPALACHIANS IN THIS AREA WILL LIKELY CONTRIBUTE TO
HEIGHTENED FLASH FLOODING RISK CONCERNS THROUGH MUCH OF THE DAY
TODAY, DESPITE SIGNIFICANTLY LESS MOISTURE AND INSTABILITY TO WORK
WITH AS COMPARED TO AREAS FURTHER SOUTH AND WEST. AN INTERNAL
HIGHER-END SLIGHT IS IN PLACE FROM THE NORTHEAST CORNER OF ALABAMA
EAST TO COVER THIS HIGHER THREAT POSED BY NEARLY CONTINUOUS
RAINFALL INTO THE TERRAIN.
..ELSEWHERE
THE MARGINAL RISK WAS EXPANDED NORTH AND WEST ACROSS PORTIONS OF
ARKANSAS AND TENNESSEE IN RESPONSE TO ONGOING CONVECTION WITH A
HISTORY OF TRAINING AND FLASH FLOODING, AS WELL AS ACROSS PORTIONS
OF CENTRAL TEXAS, WHERE TRAINING SUPERCELLS AND A BIT OF
BACKBUILDING CONVECTION NEAR THE HILL COUNTRY COULD POSE AN
ISOLATED FLASH FLOODING THREAT.
WEGMAN
DAY 2
VALID 12Z THU MAY 07 2026 - 12Z FRI MAY 08 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL GULF COAST THROUGH SOUTHERN GEORGIA AS WELL AS FOR
PORTIONS OF THE RIO GRANDE VALLEY OF SOUTH TEXAS...
..2030Z UPDATE
..CENTRAL GULF COAST THROUGH SOUTHERN GEORGIA
BY THE START OF THE PERIOD 12Z THURSDAY, THE CLASH OF AIR MASSES
BETWEEN A COOLER, DRY AIR MASS OVER MUCH OF THE INTERIOR SOUTHEAST
AND A VERY WARM, UNSTABLE, TROPICAL AIR MASS OFF THE GULF TO THE
SOUTH WILL BE WANING, WITH THE FORMER AIR MASS WINNING OUT. THE
FRONT WILL BE ON THE MOVE TOWARDS THE SOUTH AND EAST THURSDAY
MORNING. THIS WILL BE COMBINED WITH A FAST MOVING SHORTWAVE AT THE
BASE OF A DEEP LONGWAVE TROUGH TO SUPPORT THE PROGRESSIVE MOVEMENT
OF THE STORMS SOUTH AND EAST ACROSS SOUTHERN ALABAMA, SOUTH
GEORGIA, AND EVENTUALLY THE NORTHERN PANHANDLE OF FLORIDA. AS THE
FRONT MOVES OVER SOUTHERN ALABAMA AND CENTRAL GEORGIA EARLY
THURSDAY MORNING, SOME BACKBUILDING DUE TO SOUTHWESTERLY MOISTURE
ADVECTION COULD STILL RESULT IN LOCALIZED AREAS OF TRAINING BETWEEN
STORMS AS THE ENTIRE SYSTEM MOVES SOUTHEASTWARD. COMBINED WITH A
FEW BURN SCARS ACROSS FAR SOUTH GEORGIA DUE TO RECENT WILDFIRES,
THE MARGINAL RISK INHERITED WAS LARGELY LEFT UNCHANGED, OTHER THAN
TRIMMING IT BACK FROM THE SOUTH CAROLINA COAST DUE TO NATURAL FLOOD
RESISTANCE AND LESS EXPECTED RAINFALL THERE. THE FLOOD THREAT WILL
RAPIDLY DIMINISH THURSDAY AFTERNOON AS THE FRONT DISSIPATES ACROSS
NORTH FLORIDA.
..RIO GRANDE VALLEY
A WEAK AREA OF SURFACE LOW PRESSURE IS EXPECTED TO DEVELOP THURSDAY
AT THE END OF THE SAME FRONT MOVING ACROSS THE SOUTHEAST. THIS LOW
WILL HAVE ABUNDANT ATMOSPHERIC MOISTURE TO WORK WITH, SOME UPPER
LEVEL SUPPORT IN THE RIGHT ENTRANCE REGION OF A JET, AND AN
APPROACHING SHORTWAVE TROUGH OVER WEST TEXAS. THERMAL HEATING WILL
ALLOW FOR CONVECTIVE DEVELOPMENT OVER THE MOUNTAINS OF MEXICO.
WESTERLY FLOW MAY ALLOW A FEW OF THOSE STORMS TO SURVIVE TRACKING
EAST OFF THE MOUNTAINS AND ACROSS THE RIO GRANDE. WHILE MANY AREAS
OF SOUTH TEXAS HAVE VERY DRY SOILS, THE ABUNDANCE OF MOISTURE
(PWATS OVER 2 INCHES) WILL SUPPORT STORMS THAT WILL BE CAPABLE OF
MULTI-INCH-PER-HOUR RATES. THIS INTENSITY OF RAIN MAY OVERCOME THE
DRY SOILS TO RESULT IN ISOLATED INSTANCES OF FLASH FLOODING. THE
MARGINAL WAS LEFT LARGELY UNCHANGED WITH THIS UPDATE.
WEGMAN
DAY 3
VALID 12Z FRI MAY 08 2026 - 12Z SAT MAY 09 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE UPPER
TEXAS GULF COAST THROUGH THE LOWER MISSISSIPPI VALLEY...
..2030Z UPDATE
RETURN FLOW OFF THE GULF ON FRIDAY WILL RUN INTO THE SAME STALLED
FRONT THAT WILL BE LIFTING NORTH AS A WARM FRONT DURING THE DAY.
AMPLE MOISTURE WITH PWATS OF 1.75 INCHES AND UP WILL SUPPORT
NUMEROUS THUNDERSTORM DEVELOPMENT AS EARLY AS MIDDAY, THEN
CONTINUING THROUGH THE AFTERNOON, WITH ADDITIONAL STORMS IMPACTING
THE AREA LATE FRIDAY NIGHT. THIS WILL SUPPORT A RENEWED FLASH
FLOODING RISK, ESPECIALLY SINCE SEVERAL URBAN AREAS, INCLUDING
HOUSTON, SAN ANTONIO, AND NEW ORLEANS COULD BE INVOLVED. DUE TO THE
ABUNDANCE OF MOISTURE AND CONTINUING SOUTHERLY FLOW OFF THE
WESTERN GULF RESUPPLYING MOISTURE LOST TO RAINFALL, EXPECT
BACKBUILDING AND TRAINING THUNDERSTORMS TO IMPACT THE SLIGHT RISK
AREA, WHICH WILL SUPPORT WIDELY SCATTERED INSTANCES OF FLASH
FLOODING. WHILE SOME AREAS ARE STARTING OUT DRIER THAN NORMAL FOR
SOIL MOISTURE, MOST ARE RIGHT AROUND AVERAGE FOR THIS TIME OF YEAR.
THIS COULD ALLOW FOR THE STORMS TO OVERWHELM LOCAL SOILS,
ESPECIALLY IN URBAN AREAS, A BIT SOONER, CONTRIBUTING TO THE WIDELY
SCATTERED FLASH FLOODING THREAT.
WEGMAN
..PREVIOUS DISCUSSION
THE RISK OF EXCESSIVE RAINFALL WILL BE FOCUSED ALONG THE LOW-LEVEL
BOUNDARY THAT BUILDS INTO THE REGION ON DAY 2 AND STALLS ALONG A
WEST TO EAST AXIS. PRECIPITABLE WATER VALUES IN EXCESSIVE OF 1.5
INCHES SHOULD BE POOLING ALONG THE BOUNDARY ON FRIDAY...WITH HIGHER
PRECIPITABLE WATER VALUES RETURNING NORTHWARD LATER IN THE DAY ON
FRIDAY AND THROUGH FRIDAY NIGHT/EARLY SATURDAY MORNING.
SOUTHERN STREAM SHORTWAVE ENERGY BECOME SOUTHERLY DURING THE DAY
AND INCREASES.
THE MARGINAL RISK AREA IS CONDITIONAL IN THE SENSE THAT A SLIGHT
COULD BE NEEDED DEPENDING ON OBSERVED RAINFALL ON DAY 2, THE
DEGREE OF OVERLAP WITH DAY 3 QPF AND THE AMOUNT OF URBANIZATION.
BANN
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
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