023
FOUS30 KWBC 061512
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1112 AM 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 RFR 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
TEXAS EASTWARD TO GULF COAST REGION AND SOUTHEAST UNITED STATES...
ABUNDANT MOISTURE ALONG A STALLED FRONTAL BOUNDARY ON THURSDAY
WILL SUPPORT ADDITIONAL THUNDERSTORM FORMATION ALONG THE FRONT.
RAPIDLY WEAKENING FORCING AT THE SURFACE AND ALOFT WILL GREATLY
DIMINISH CONVECTIVE COVERAGE AND RESTRICT THE PARAMETERS FAVORABLE
FOR HEAVY TO EXCESSIVE RAINFALL ALONG THE GULF COAST AND INTO
CENTRAL GEORGIA AND SOUTH CAROLINA. GIVEN DIFFERENCES IN THE WAY
NUMERICAL GUIDANCE HAS IN TERMS OF HOW FAST THE FRONT IS
PROGRESSING...THERE WAS SOME CONTINUED ADJUSTMENTS TO THE PLACEMENT
OF THE MARGINAL RISK AREA.
SOUTH TX BRUSH COUNTRY...
AN UPPER LOW WITH AN ASSOCIATED SURFACE BOUNDARY APPROACHING THE
REGION SHOULD LEAD TO INCREASING CHANCES FOR SHOWERS AND
THUNDERSTORMS. EXPECTATIONS ARE THAT MOST OF THE CONVECTION IN THIS
TIME FRAME WILL REMAIN WEST OF THE INTERNATIONAL BORDER BUT THERE
ARE ENOUGH MODELS SHOWING SOME STORMS MAKING EAST OF THE RIO GRANDE
RIVER WITH ISOLATED HEAVIER AMOUNTS AND INFERRED RAINFALL RATES
THAT COULD LEAD TO ISOLATED FLOODING CONCERNS DURING THE LATE
DAY/EVENING.
BANN
DAY 3
VALID 12Z FRI MAY 08 2026 - 12Z SAT MAY 09 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE LOWER- AND CENTRAL TEXAS COAST ON FRIDAY...
ATTENTION SHIFTS TO THE LOWER TEXAS COAST FOR A RISK OF EXCESSIVE
RAINFALL AS SHORTWAVE ENERGY NEARS THE REGION FROM THE SOUTHERN
GREAT BASIN AND NORTHERN MEXICO. LOW LEVEL FLOW BACKS IN RESPONSE
TO THE APPROACHING SHORTWAVE WHICH RESULTS IN PRECIPITABLE WATER
VALUES TO EXCEED 2 INCHES ALONG THE IMMEDIATE COASTLINE. THIS
OCCURS AT THE SAME TIME FLOW ALOFT IS EXPECTED TO BECOME
INCREASINGLY DIFFLUENT AND WHEN THE CAPE IS APPROACHING 1000 J PER
KG. THIS SHOULD RESULT IN GROWING COVERAGE OF CONVECTION THAT WILL
BE CAPABLE OF PRODUCING RAINFALL RATES SUFFICIENTLY HIGH TO RESULT
IN ISOLATED INSTANCES OF FLASH FLOODING.
BANN
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE GULF COAST AND SOUTHEAST UNITED STATES...
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
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