855
FOUS30 KWBC 290056
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
856 PM EDT THU MAY 28 2026
DAY 1
VALID 01Z FRI MAY 29 2026 - 12Z FRI MAY 29 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF THE
MID-SOUTH AND OZARKS...
01Z UPDATE...
HAVE DROPPED THE MARGINAL RISK ACROSS MUCH OF THE SOUTHEAST
(OUTSIDE OF SE FL), GIVEN THE LACK OF DEEP LAYER FORCING, DECAYING
DIURNAL HEATING AND SEA BREEZES, AND WEAK MID LEVEL LAPSE RATES.
DESPITE BETTER FORCING (ALONG MID LEVEL DEFORMATION AXIS/TROWAL
ZONE), DIMINISHING DEEP-LAYER INSTABILITY HAS ALSO ALLOWED FOR THE
SLIGHT RISK OVER KS TO DROP TO A MARGINAL. OTHERWISE, THE SLIGHT
OVER CENTRAL-NORTHERN AR INTO SOUTHWEST AND SOUTH-CENTRAL MO
CONTINUES, BASED ON THE LATEST OBSERVATIONAL TRENDS (RADAR,
SATELLITE, MESOANALYSIS), ALONG WITH RECENT HRRR TRENDS AND
ELEVATED QPF EXCEEDANCE PROBABILITIES FROM THE 18Z HREF.
HAVE ALSO EXPANDED THE MARGINAL RISK OVER THE NORTHERN ROCKIES AND
INTERMOUNTAIN WEST AREAS, BASED LARGELY ON CURRENT OBSERVATIONAL
TRENDS.
HURLEY
---PREVIOUS DISCUSSION---
..FLORIDA
AN ACTIVE SEA BREEZE PATTERN WITH WEAKENING STEERING FLOW WILL
LEAD TO PERIODS OF HEAVY RAINFALL ACROSS SOUTHEAST FLORIDA THIS
AFTERNOON. GREATEST CONCERN REMAINS OVER THE SOUTH FLORIDA METRO
CORRIDOR FROM WEST PALM BEACH TO MIAMI. LATEST HREF IS ROBUST WITH
SHOWING GREATER THAN 50% PROBABILITIES FOR 3" IN 24-HOURS, WITH
EVEN SOME MODEST, ALBEIT LOCALIZED, PROBABILITIES FOR 5". THIS
CORRELATES WELL WITH CAM GUIDANCE, WITH SOME INDICATING BULLSEYES
OF GREATER THAN 3" WITHIN THE LARGER QPF FOOTPRINT. LOCALLY
SIGNIFICANT RAINFALL IS LIKELY IN THIS RELATIVELY CLASSIC PATTERN
WITH AMPLE MOISTURE AND INSTABILITY PRESENT. A MARGINAL RISK
REMAINS IN EFFECT ACROSS SOUTHEAST FLORIDA.
..WASHINGTON/OREGON
A DEEP UPPER LEVEL LOW OVER THE WEST WILL ALLOW FOR A BROAD AXIS
OF DIFFLUENT FLOW ACROSS THE INTERIOR NORTHWEST. PRECIPITABLE WATER
VALUES 1-1.5" ARE IN THE 90-90TH PERCENTILE, AND WITH SUFFICIENT
INSTABILITY, SHOULD SUPPORT CONVECTION CAPABLE OF PRODUCING HEAVY
RAINFALL. FLOODING AND FLASH FLOODING ARE A CONCERN FOR MAINLY THE
MORE VULNERABLE AREAS - URBAN, SMALL STREAM, AND LOW LYING AREAS.
HREF 24-HR PROBABILITIES FOR GREATER THAN 3" ARE BETWEEN 40-70% FOR
ESPECIALLY THE OREGON CASCADES. GIVEN THE FAVORABLE ENVIRONMENT
THOUGH, A MARGINAL RISK EXTENDS ALL THE WAY FROM FAR NORTHERN
CALIFORNIA NORTHWARD TO THE EASTERN HALF OF WASHINGTON STATE. A
PREVIOUS MARGINAL RISK FOR PARTS OF THE NORTHERN ROCKIES WAS
TRIMMED OUT FOR THIS UPDATE GIVEN THE LACK OF QPF SIGNAL.
SANTORELLI
DAY 2
VALID 12Z FRI MAY 29 2026 - 12Z SAT MAY 30 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHEAST...
20Z UPDATE...
IN COLLABORATION WITH SEVERAL SOUTHEAST WFOS, A SLIGHT RISK WAS
INTRODUCED FROM EASTERN AL TO THE GA/SC BORDER. THE REGION IS
CAUGHT OUT AHEAD OF A SHEARED 500MB VORTICITY MAXIMUM APPROACHING
FROM THE WEST. THIS FEATURE IS CAUGHT BETWEEN A CLOSED LOW
TRAVERSING THE GREAT BASIN, AN UPPER LEVEL RIDGE IN THE MIDWEST,
AND A STRONG TROUGH IN THE NORTHEAST. AT LOWER LEVELS, WEAK HIGH
PRESSURE OVER THE FL STRAITS AND TROUGHING IN THE WESTERN GULF IS
PRODUCING A LENGTHY MOISTURE FETCH WITH ORIGINS IN THE CARIBBEAN
SEA. BY 00Z SAT, ECMWF SATS SHOWS A >90TH CLIMATOLOGICAL PERCENTILE
IVT ORIENTED N-S AND DIRECTED AT THE SOUTHEAST. THIS CULMINATES IN
A TROPICAL AIR-MASS SPORTING 2.0-2.2" PWS THAT IS DIRECTED AT A
STATIONARY FRONT IN DRAPED FROM THE TN VALLEY TO THE SC COAST.
INSTABILITY WILL BE HIGHEST OVER AL ON EAST INTO CENTRAL AND
SOUTHERN GA WITH MUCAPE BETWEEN 1,000-2,000 J/KG MOST OFTEN. MUCAPE
UP TO 1,000 J/KG WILL BE AVAILABLE FRIDAY NIGHT FROM THE SAVANNAH
RIVER TO COASTAL SC.
AREA-AVERAGED SOUNDINGS SHOW WARM CLOUD LAYERS AS DEEP AS 13,000FT
OVER EASTERN GA AT THE SAME TIME AS A WEAK, YET NEGATIVELY-TILTED
250MB TROUGH FOSTERS SYNOPTIC-SCALE ASCENT ALOFT. GUIDANCE SHOWS
A CLUSTER OF HEAVY THUNDERSTORMS FORMING THAT WILL SLOWLY MAKE
THEIR WAY EAST. THE SLIGHT RISK AREA RESIDES JUST SOUTH OF THE
STALLED FRONT WHERE GREATER INSTABILITY WILL RESIDE AND ATOP SOME
OF THE MORE SATURATED SOILS IN THE REGION. THE STRONGEST STORMS
WILL HAVE THE CAPABILITY TO PRODUCE MAX RATES UP TO 3"/HR RAINFALL
RATES FROM EASTERN AL ON EAST TO THE SAVANNAH RIVER FRIDAY
AFTERNOON AND THROUGH FRIDAY NIGHT. WITH INCREASED CONFIDENCE IN
LOCALLY CONSIDERABLE RAINFALL RATES OVER SENSITIVE SOILS, A SLIGHT
RISK WAS INTRODUCED.
OTHERWISE, SOME MINOR TWEAKS TO THE INHERITED MARGINAL RISK AREAS
WERE MADE IN THE CENTRAL PLAINS AND NORTHERN ROCKIES TO ACCOUNT FOR
THE LATEST WPC QPF.
MULLINAX
---PREVIOUS DISCUSSION---
..EASTERN WASHINGTON TO NORTHERN ROCKIES
A MARGINAL RISK IS IN PLACE ACROSS FAR NORTHEAST WASHINGTON TO
NORTHWEST MONTANA DUE TO AN INCREASE IN THE HEAVY RAINFALL SIGNAL
FOR THIS PERIOD AS THE UPPER LOW OVER THE WEST ON DAY 1, PIVOTS
SLIGHTLY NORTHEASTWARD, PLACING THIS REGION IN AN AREA WITH BETTER
UPPER FORCING AND ADVECTION OF MOISTURE. THE PRESENCE OF ANOMALOUS
MOISTURE AND SOME INSTABILITY MAY PRESENT A THREAT FOR LOCALIZED
HEAVY RAINFALL AND FLASH FLOODING, ESPECIALLY FOR BURN SCAR
LOCATIONS WITHIN THIS REGION.
..MIDDLE MISSISSIPPI VALLEY TO THE SOUTHEAST
STRONG CANADIAN HIGH PRESSURE PRESSING IN FROM THE NORTH WILL
ALLOW FOR A SLOW MOVING COLD FRONT TO PRESS SOUTH OVER THE COURSE
OF THURSDAY INTO FRIDAY WITH CONVECTION LIKELY TO SPAWN ALONG AND
AHEAD OF THE FRONT AND DRY AIR ADVECTING BEHIND THE FRONT LEADING
TO A QUICK CUTOFF OF ACTIVITY. THE FRONT WILL ARC BACK INTO THE
TENNESSEE VALLEY TO MIDDLE MISSISSIPPI VALLEY, SUPPORTED BY THE
PERSISTENT TROUGHING OVER THE SOUTH-CENTRAL PLAINS. A MOIST AND
UNSTABLE ENVIRONMENT NEAR AND SOUTH OF THIS FRONT WILL SUPPORT
SCATTERED CONVECTION, WITH SOME HEAVIER CELLS LIKELY WITHIN THE
PATTERN. IT IS STILL TOO HARD TO PICK OUT ANY DISCERNIBLE AREAS OF
INTEREST, SO MAINTAINED A VERY BROAD MARGINAL RISK OVER THIS AREA
WHICH IS QUITE WET AND WILL CONTINUE TO BE IN THE DAY 1 PERIOD.
SANTORELLI
DAY 3
VALID 12Z SAT MAY 30 2026 - 12Z SUN MAY 31 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE
NORTHERN ROCKIES TO HIGH PLAINS AND THE SOUTHEAST...
20Z UPDATE...
THERE WAS CONSIDERATION GIVEN TO A SLIGHT RISK OVER EASTERN GA ON
EAST THOUGH MUCH OF COASTAL SC GIVEN THE SAME SETUP SUPPORTING A
SLIGHT RISK FARTHER WEST ON FRIDAY SHOULD MOVE EAST SATURDAY
MORNING. HOWEVER, LINGERING MODEL SPREAD IN BOTH AMOUNTS AND THE
AXIS OF HEAVIER RAINFALL (AS FAR NORTH AS NORTHERN SC, AS FAR SOUTH
AS THE FL PANHANDLE) MADE IT DIFFICULT TO PINPOINT A MORE "AT-
RISK" AREA. THE COASTAL AREAS OF THE SOUTHEAST WILL BE MONITORED
CLOSELY IN THE COMING FORECAST CYCLES, BUT OPTED TO MAINTAIN A
MARGINAL RISK GIVEN THE LINGERING UNCERTAINTY. MEANWHILE, IN THE
NORTHERN ROCKIES, PLENTY OF PRECIPITATION IS LIKELY COMING TO THE
REGION ON SATURDAY. THE PRIMARY REASON FOR NO SLIGHT RISK IS DUE TO
THE POTENTIAL FOR LARGE SUMS OF CLOUDS POSSIBLY REDUCING THE
INSTABILITY AVAILABLE. THIS SHOULD BE A BENEFICIAL SOAKING RAIN
EVENT FOR DROUGHT-STRICKEN CENTRAL MT, BUT LOCALIZED AREAS OF FLASH
FLOODING ARE POSSIBLE IN POOR DRAINAGE AREAS AND ALONG COMPLEX
TERRAIN.
MULLINAX
---PREVIOUS DISCUSSION---
..NORTHERN ROCKIES TO HIGH PLAINS
THE UPPER LEVEL LOW OVER THE WEST DURING THE DAY 1 AND 2 PERIODS
WILL WEAKEN AND SHIFT NORTHEASTWARD, MOVING OVER THE NORTHERN
ROCKIES TO HIGH PLAINS REGION ON DAY 3/SATURDAY. MOISTURE ANOMALIES
WILL CONTINUE TO BE IN THE 90-90TH PERCENTILE, SUPPORTING MODERATE
TO HEAVY RAINFALL, WITH WIDESPREAD QPF GREATER THAN 0.5-1" LIKELY
ACROSS WESTERN AND CENTRAL MONTANA. THERE MAY NOT BE A LOT OF
INSTABILITY TO WORK WITH, SO ANY FLOOD OR FLASH FLOOD THREATS
SHOULD BE MAINLY LOCALIZED WITH PARTICULAR ATTENTION TO BURN SCAR
LOCATIONS. A FAIRLY BROAD MARGINAL RISK IS IN PLACE ACROSS MUCH OF
WESTERN AND CENTRAL MONTANA, INTO PARTS OF NORTHERN WYOMING AS
WELL.
..SOUTHEAST
SAME STORY AS DAYS 1 AND 2, WITH AMPLE MOISTURE AND INSTABILITY
PRESENT NEAR AND SOUTH OF A COLD FRONT THAT MAY STALL OVER THE
REGION ON SATURDAY SUPPORTING CONVECTION, ACROSS MUCH OF THE
SOUTHEAST. SOME OF THIS REGION, ESPECIALLY WESTERN PARTS OF SOUTH
CAROLINA AND INTO THE APPALACHIANS HAS BEEN VERY WET AS OF LATE AND
IS WELL PRIMED, SO MAY BE MORE FAVORABLE FOR FLOODING CONCERNS.
THE MARGINAL RISK THOUGH CONTINUES TOWARDS THE COAST DUE TO THE
PRESENCE OF A WEAK FRONTAL WAVE IN THE REGION. THE MARGINAL RISK
EXTENDS FROM THE SOUTHEAST COAST, WESTWARD INTO NORTHEAST ALABAMA
AND SOUTHEAST TENNESSEE.
SANTORELLI
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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