628
FOUS30 KWBC 281558
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1158 AM EDT THU MAY 28 2026
DAY 1
VALID 16Z THU MAY 28 2026 - 12Z FRI MAY 29 2026
...THERE ARE SLIGHTS RISKS OF EXCESSIVE RAINFALL ALONG THE CENTRAL
GULF COAST, CENTRAL KANSAS, AND IN THE OZARKS OF MISSOURI AND
ARKANSAS...
16Z UPDATE...
SLIGHT RISKS WERE INTRODUCED FOR THE 16Z UPDATE IN PARTS OF THE
CENTRAL KS, THE OZARKS, AND ALONG THE CENTRAL GULF COAST. THE
MARGINAL RISKS IN THE PACIFIC NW AND SOUTH FL REMAIN IN GOOD SHAPE.
..CENTRAL GULF COAST
THE 12Z LIX SOUNDING WAS EFFECTIVELY A TROPICAL SOUNDING WITH
PLENTY OF MLCAPE PRESENT (>2,000 J/KG). WINDS WITHIN THE DEPTH OF
THE CLOUD LAYER WERE ALMOST UNIFORMLY OUT OF THE SOUTH WITH
TRAINING THUNDERSTORMS A CONCERN FROM NOLA NON NORTH AND EAST ALONG
THE I-59 CORRIDOR. SOILS REMAIN HIGHLY SATURATED AND PRIMED FOR
FLASH FLOODING WITH RAINFALL RATES THAT COULD TOP 3"/HR IN THE
HEAVIEST THUNDERSTORM ACTIVITY. STORMS ARE AT LEAST MOVING ALONG AT
A STEADY CLIP, WHICH SHOULD HELP TO REDUCE THE AREAL EXTENT FOR
FLASH FLOODING. THAT SAID, THESE STORMS MAY EXACERBATE THE FLOODING
THE REGION HAS EXPERIENCED IN RECENT DAYS. FOR THESE REASONS, A
SLIGHT RISK WAS INTRODUCED.
..OZARKS & CENTRAL ARKANSAS
A NARROW NW-SE CORRIDOR OF ANOMALOUS PWS (>2.0" PWS THAT TOP THE
99.5 CLIMATOLOGICAL PERCENTILE PER ECMWF) IS CAUGHT BETWEEN A
STRONG RIDGE OF HIGH PRESSURE IN THE UPPER MS VALLEY AND A
NEGATIVELY TILTED 850-300MB TROUGH ORIENTED FROM SOUTHERN KS TO THE
ARKLATEX. STRONG VERTICAL ASCENT AHEAD OF THE 850-300MB TROUGH
AXIS COUPLED WITH MLCAPE BETWEEN 500-1,000 J/KG WILL GIVE MORE
SUPPORT TO THESE HIGHLY SATURATED PROFILES. AREA-AVERAGED
SOUNDINGS OVER NORTHERN AR SHOW >85% RH VALUES BETWEEN 1000-500MB
AND WARM CLOUD LAYERS >13,000FT THIS AFTERNOON AND EVENING. SOILS
ARE MOST SENSITIVE IN CENTRAL AR, WHILE THE OZARKS ARE HISTORICALLY
A "FLASHY" AREA THAT, EVEN WITH SOME DRIER SOIL MOISTURE VALUES IN
SOUTHERN MO ARE PRONE TO FLASH FLOODING GIVEN RAINFALL RATES COULD
SURPASS 2"/HR. THE 12Z HREF DOES SHOW HIGH CHANCE PROBABILITIES
(>70%) FOR RAINFALL AMOUNTS >3" IN SOUTHWEST MO AND NORTHERN AR,
WITH LOW CHANCE PROBABILITIES (20-35%) FOR >5" AMOUNTS. IN
COLLABORATION WITH WFOS IN NORTHERN AR AND SOUTHERN MO, OPTED TO
UPGRADE TO A SLIGHT RISK FOR THE 16Z UPDATE.
..CENTRAL KS
A PIVOTING 700MB LOW ROTATING THROUGH SOUTHERN KS WILL DIRECT A
PLUME OF HIGHLY ANOMALOUS MOISTURE FOR LATE MAY/EARLY JUNE OVER THE
HEART OF KS. PER RAP MESOANALYSIS, PWS ARE ALREADY >1.5" AND COULD
SURPASS 1.75" THIS AFTERNOON. CENTRAL KS IS IDEALLY PLACED JUST
AHEAD OF A NEGATIVELY TILTED 850-300MB TROUGH THAT IS GENERATING
EXCELLENT UPPER-LEVEL DIVERGENCE. ADDITIONAL STORMS WILL FORM THIS
AFTERNOON WITH HRRR AREA-AVERAGED SOUNDINGS SHOWING >500 J/KG OF
MLCAPE, >85% RH VALUES WITHIN THE MEAN 1000-500MB LAYER, AND WARM
CLOUD LAYERS UP TO 12,000FT DEEP. WIND MORE UNIFORMLY OUT OF THE SE
ARE ALSO SUPPORTING THE POTENTIAL FOR TRAINING STORMS, EVIDENT
FROM UPSHEAR CORFIDI VECTORS THAT ARE AS LOW AS 10 KTS. NEW 12Z
HREF PROBABILITIES SHOW HIGH CHANCE (>70%) FOR RAINFALL TOTALS >3"
FROM WICHITA ON NORTH AND WEST WITH LOW-TO-MODERATE CHANCES
(20-40%) FOR LOCALIZED AMOUNTS >5". SOILS IN THE AREA ARE PARCHED,
BUT THESE KIND OF RATES CAN STILL SUPPORT FLASH FLOODING,
PARTICULARLY WHERE REPEATING ROUNDS OF STORMS OCCUR AND IN MORE
URBANIZED SETTINGS. IN COLLABORATION WITH ICT, DECIDED TO UPGRADE
TO A SLIGHT RISK FOR THE 16Z UPDATE.
MULLINAX
---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 MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF
THE NORTHERN ROCKIES AS WELL AS MUCH OF THE SOUTHEAST TO MIDDLE
MISSISSIPPI VALLEY...
..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...
..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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