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FOUS30 KWBC 280054
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
854 PM EDT WED MAY 27 2026
DAY 1
VALID 01Z THU MAY 28 2026 - 12Z THU MAY 28 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
WEST VIRGINIA AND ACROSS SOUTHWEST LOUISIANA...
..0100 UTC UPDATE
HAVE TRIMMED QUITE A BIT OF REAL ESTATE WITH BOTH THE SLIGHT AND
MARGINAL AREAS, BASED ON THE LATEST OBSERVATIONAL TRENDS, INCLUDING
MESOANALYSIS (DCAPE/DT), ALONG WITH THE RECENT HRRRS AND 18Z HREF
QPF EXCEEDANCE PROBABILITIES. THE REMAINING SLIGHT RISK AREA OVER
CENTRAL WV (AND A SMALL SLIVER OF NORTHEAST KY/SOUTHEAST OH) IS
ESSENTIALLY FOR THE NEAR TERM...THROUGH 03-04Z...GIVEN THE CURRENT
RADAR TRENDS AND LINGERING DEEP-LAYER INSTABILITY (MUCAPES ~1000
J/KG). THE OTHER REMAINING SLIGHT RISK AREA (SOUTHWEST LA) WAS
SUPPORTED BY THE LATEST HREF AND RRFS EXCEEDANCE PROBABILITIES,
ALONG WITH THE RECENT HRRR OUTPUT.
HURLEY
ELSEWHERE (NORTHERN ROCKIES), THE MARGINAL RISK AREA REMAINS
(PREVIOUS DISCUSSION BELOW)...
RELATIVELY BUOYANT ENVIRONMENT WITHIN A DEEP, ANOMALOUS MOISTURE
PRESENCE ACROSS THE NORTHERN ROCKIES ALONG WITH REGIONAL ASCENT
PROVIDED BY SHEARED VORTICITY MAXIMA MANEUVERING THROUGH THE AREA
WILL ALLOW FOR ANOTHER ROUND OF WIDELY SCATTERED CONVECTION TO
MATERIALIZE ACROSS THE LEWIS RANGE IN NORTHWEST MT. INSTABILITY AND
REGIONAL FORCING WILL BE A BIT LESS THAN THE PREVIOUS PERIOD,
HOWEVER SENSITIVITIES REMAIN FROM REMNANT BURN SCARS PRESENT WITHIN
THE MOUNTAINOUS TERRAIN IN THE AFOREMENTIONED AREA WHICH IS A
CAUSE FOR CONCERN FOR ANY CELLS THAT HAPPEN TO OCCUR OVER THE BURN
SCARS THEMSELVES. HOURLY RATES BETWEEN 0.5-1"/HR IN THE STRONGER
CELL CORES WOULD BE CAPABLE OF PROVIDING LOCALIZED FLASH FLOOD
IMPACTS OVER THOSE MORE SENSITIVE GROUNDS AND THIS SETUP WILL
MAINTAIN THE PROSPECTS GIVEN THE ANOMALOUS MOISTURE PRESENCE AS
PWATS REMAIN ABOVE THE 90TH PERCENTILE OVER THE ENTIRE STRETCH OF
THE NORTHERN ROCKIES. THE PREVIOUS MRGL RISK INHERITED WAS
MAINTAINED GIVEN THE RELATIVE CONTINUITY.
KLEEBAUER
DAY 2
VALID 12Z THU MAY 28 2026 - 12Z FRI MAY 29 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE CENTRAL AND SOUTHERN PLAINS, PACIFIC NORTHWEST INTO THE
NORTHERN ROCKIES, LOWER MISSISSIPPI VALLEY, AND SOUTHEAST
FLORIDA...
..PLAINS TO LOWER MISSISSIPPI VALLEY
21Z UPDATE... THE REGION WITH A HIGHLIGHTED THREAT FOR EXCESSIVE
RAINFALL AND ISOLATED FLASH FLOODING REMAIN IN GOOD ORDER,
REQUIRING NO ADJUSTMENTS AT THIS TIME.
CAMPBELL
A BIT OF AN OMEGA BLOCK PATTERN IS SHAPING UP ACROSS THE CONUS WITH
A BROAD UPPER TROUGH AXIS FIXATED OVER THE CENTRAL AND SOUTHERN
PLAINS WITH WITH RIDGING IN PLACE OVER THE TOP. THIS WILL CAUSE A
RATHER CHAOTIC FLOW UNDER THE MEAN TROUGH WITH DEEP MOISTURE AND
SEVERAL SMALLER MID-LEVEL PERTURBATIONS BASICALLY "STUCK" UNDER THE
THE OVERALL TROUGH AXIS. AMPLE INSTABILITY WITH DEEP MOISTURE
PRESENCE WILL CERTAIN BE A CAUSE FOR CONTINUING AT LEAST A
SCATTERED HEAVY RAIN FOOTPRINT ACROSS AREAS UNDER THE INFLUENCE OF
THE TROUGH. SCATTERED ELEVATED PROBABILITIES BETWEEN 30-60% EXISTS
FOR LOCALIZED AMOUNTS >2" FROM KS ALL THE WAY INTO THE SOUTHEAST
U.S. WITH THE MAXIMA SPLIT BETWEEN KS AND THE CENTRAL GULF COAST.
THE TWO AREAS ARE DIFFERENT IN THE REASONING AS THE PRIMARY CENTER
OF THE TROUGH WILL BE FIXED OVER KS LEADING TO THE BEST UPPER
FORCING PATTERN AND STAGNANT FLOW REMAINING PARKED OVER THE AREA AS
WE MOVE THROUGH D2. PENDING THE AMOUNT OF RAIN THAT FALLS OVER THE
COURSE OF D1, A TARGETED UPGRADE IS POSSIBLE, BUT MAINTAINED THE
MRGL AND WILL REASSESS AS WE MOVE FORWARD IN FUTURE UPDATES TO SEE
IF AN UPGRADE IS WARRANTED. THE CENTRAL GULF COAST WILL REMAIN IN A
FAVORABLE INSTABILITY MAXIMA WITH WEAK FLOW LIKELY A COMPONENT THAT
COULD LEAD TO ISOLATED HEAVY TOTALS STEMMING FROM SLOW-MOVING
CONVECTION. THE AREA FROM THE UPPER TX COAST OVER THROUGH SOUTHERN
GA HAS BEEN LEANING WET OVER THE PAST WEEK, SO ANTECEDENT
CONDITIONS ARE A LITTLE MORE UNFORGIVING FOR THESE TYPES OF SETUPS.
IN ANY CASE, THE THREAT REMAINS MODEST, AT BEST, SO THE MRGL RISK
WAS SUFFICIENT FOR THE PATTERN WITH ANY UPGRADES LIKELY TO STEM
FROM MORE NEAR TERM SAMPLING OF THE RADAR TRENDS.
..FLORIDA
21Z UPDATE... NO CHANGES WERE MADE FOR THIS PERIOD.
CAMPBELL
ACTIVE SEA BREEZE PATTERN WITH WEAKENING STEERING FLOW WILL LEAD
TO A PERIOD OF HEAVY RAINFALL ACROSS THE SOUTHEAST FL COAST ON
THURSDAY AFTERNOON. CONSENSUS WITHIN GUIDANCE IS FOR AN ACTIVE
PERIOD BETWEEN 18-00Z THU/FRI THAT WOULD ALLOW FOR HEAVY CONVECTION
WITH SLOW FORWARD PROPAGATIONS TO IMPACT THE SOUTH FLORIDA METRO
CORRIDOR FROM WEST PALM BEACH DOWN TO MIAMI. LATEST 00Z HREF IS
MODESTLY ROBUST WITH THE SIGNATURE FOR AT LEAST 3" OFF THE
NEIGHBORHOOD PROBABILITIES WITH A STEADY 60-90% OUTPUT ALONG THE
SOUTHEASTERN COAST OF FL WITH THE MAXIMA GENERALLY CONFINED TO THE
MIAMI METRO UP TO WEST PALM BEACH. THIS CORRELATES STRONGLY WITH
WHAT HAS BEEN ADVERTISED VIA REGIONAL AND GLOBAL GUIDANCE THE PAST
FEW DAYS WITH THE DETERMINISTIC CAMS EVEN INDICATING SOME 4-6"
BULLSEYE'S WITHIN THE MAIN QPF FOOTPRINT. THIS IS A RELATIVELY
CLASSIC PATTERN CAPABLE OF LOCALLY SIGNIFICANT RAINFALL WITHIN A
DEEP MOISTURE PRESENCE AS PWAT ANOMALIES SIT BETWEEN +1 TO +2
STANDARD DEVIATIONS WITHIN THE VARIOUS ENSEMBLE PACKAGES. A MRGL
RISK REMAINS IN EFFECT FOR THE PERIOD ACROSS THE SOUTH FLORIDA
METRO CORRIDOR.
..WASHINGTON/OREGON INTO THE NORTHERN ROCKIES
21Z UPDATE... A SUBSTANTIAL EXPANSION OF THE NORTHERN ROCKIES
MARGINAL RISK WAS MADE TO INCLUDE MOST OF EASTERN WASHINGTON UP TO
THE CONTINENTAL DIVIDE AND SOUTH INTO THE OREGON CASCADES AND
SURROUNDING AREAS ON BOTH SIDES OF THE DIVIDE. ANOMALOUS PW VALUES
HAVE BEEN OBSERVED ACROSS THE REGION, WITH SOME NEARING THE
CLIMATOLOGY MAX FOR LATE MAY. SHOULD THUNDERSTORMS HOLD TOGETHER,
ESPECIALLY WEST OF THE CASCADES, THERE WILL BE AN ELEVATED THREAT
FOR LOCAL FLASH FLOODING.
CAMPBELL
MATURING ULL OVER THE WEST COAST WILL ALLOW FOR A BROAD AXIS OF
DIFFLUENT FLOW ACROSS THE INTERIOR NORTHWEST WITH THE HIGHLIGHT OF
SCATTERED CONVECTION LIKELY TO PIVOT FURTHER WEST INTO EASTERN WA,
NORTHERN ID, AND THE WESTERN SLOPES OF THE NORTHERN ROCKIES.
SIGNALS ARE NOT AS PREVALENT COMPARED TO PREVIOUS PERIODS, HOWEVER
THE ENVIRONMENTAL CONDITIONS ARE STILL FAVORABLE, ESPECIALLY WHEN
IT COMES TO PWAT ANOMALIES STILL GENERALLY RUNNING BETWEEN THE
90-95TH PERCENTILE ACROSS NORTHEAST WA INTO NORTHERN ID. BURN SCAR
REMNANTS WILL LIKELY BE THE MOST SUSCEPTIBLE TO SEEING IMPACTS, SO
THE THREAT REMAINS LOW-END AND GENERALLY LOCALIZED. MAINTAINED
CONTINUITY FROM THE PREVIOUS FORECAST WITH A MRGL RISK IN PLACE
ACROSS THE AFOREMENTIONED AREAS.
KLEEBAUER
DAY 3
VALID 12Z FRI MAY 29 2026 - 12Z SAT MAY 30 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHEAST U.S. AND FOR EASTERN WASHINGTON INTO THE NORTHERN
ROCKIES...
21Z UPDATE... A MARGINAL RISK WAS RAISED FOR PORTIONS OF EASTERN
WASHINGTON, NORTHERN IDAHO AND NORTHWEST MONTANA WHERE THERE HAS
BEEN AN ELEVATED THREAT FOR LOCALIZED EXCESSIVE RAINFALL AND
ISOLATED FLASH FLOODING AS DESCRIBED IN THE DAY 1 AND DAY 2
SECTIONS. GUIDANCE IS SIGNALING A NOTABLE INCREASE IN QPF AMOUNTS
AND COVERAGE FOR PARTS OF NORTHERN IDAHO AND INTO MONTANA, THUS
CONTINUING THE FLOODING THREAT FOR THIS TIME PERIOD.
FURTHER SOUTH, GUIDANCE STILL VARIED ON WHERE THE HIGHEST QPF WAS
PLACED; HOWEVER THERE WAS CONSENSUS FOR AN INCREASE IN AMOUNTS
ACROSS SOUTHERN MISSOURI, CENTRAL/EASTERN TENNESSEE AND WESTERN
SOUTH CAROLINA. THIS TREND SUPPORTED AN ADJUSTMENT OF THE NORTHERN
BOUNDARY OF THE MARGINAL RISK AREA.
CAMPBELL
STRONG CANADIAN HIGH PRESSURE PRESSING IN FROM THE NORTH WILL LEAD
TO A PERSISTENT QUASI-STATIONARY TURNED COLD FRONT TO PRESS SOUTH
OVER THE COURSE OF THURSDAY INTO FRIDAY WITH CONVECTION LIKELY TO
SPAWN ALONG AND AHEAD OF THE FRONT WITH DRY AIR ADVECTING BEHIND
THE FRONT LEADING TO A CUTOFF OF ACTIVITY. JURY IS STILL OUT ON
SPECIFICS WITH THE PLACEMENT OF THE FRONT GENERALLY OVER THE
CAROLINA'S BY FRIDAY MORNING WITH SLOW PUSH SOUTH AS THE DAY WEARS
ON. FRONTAL ALIGNMENT IS MORE OF A ARCING BACK INTO THE TENNESSEE
VALLEY AS THE PERSISTENT TROUGHING IN THE SOUTH-CENTRAL PLAINS WILL
LIKELY MAINTAIN SOME SOUTHERLY FLOW FOR AREAS ALONG AND WEST OF THE
MISSISSIPPI. ANYWHERE WITHIN PROXIMITY TO THIS FRONT WILL BE
SUBJECT TO VARIOUS CONVECTIVE OUTPUTS WITH SOME HEAVIER CELLS
LIKELY INTERTWINED IN OVER THE PATTERN. NO DISCERNIBLE AREAS OF
INTEREST ARE PRESENT AT THIS JUNCTURE, HOWEVER THE ENVIRONMENTAL
FAVORABILITY LIKELY POINTS TO THE BEST CHANCES OCCURRING ACROSS
THE SOUTHEAST INTO THE LOWER TENNESSEE VALLEY. A BROAD MRGL IS
FORECAST FOR THE ABOVE AREAS THROUGH THE LOWER MISSISSIPPI VALLEY.
KLEEBAUER
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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