019
FOUS30 KWBC 270017
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
817 PM EDT TUE MAY 26 2026
DAY 1
VALID 01Z WED MAY 27 2026 - 12Z WED MAY 27 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
CENTRAL AND SOUTHERN TEXAS...
..TEXAS INTO SOUTHERN OKLAHOMA
..0100 UTC UPDATE
BASED ON THE LATEST OBSERVATIONAL TRENDS -- SATELLITE, RADAR,
MESOANALYSIS, ETC. -- HAVE PARED THE BACK EDGES OF THE OUTLOOK
AREAS ACROSS WEST TX. ALSO NUDGED THE SOUTHERN PERIPHERY OF THE
SLIGHT RISK AREA A LITTLE FARTHER SOUTH ACROSS SOUTH TX (BRUSH
COUNTRY), BASED ON THE LATEST HRRR TRENDS AND ELEVATED 18Z HREF
EXCEEDANCE PROBABILITIES. OVER THIS REGION, STILL QUITE A BIT OF
UNTAPPED DEEP-LAYER INSTABILITY (MIXED-LAYER CAPES ~3,000 J/KG),
ALONG WITH PWATS BETWEEN 1.9-2.1 PER THE LATEST SPC MESOANALYSIS.
CONTINUED LOW-MID LEVEL SHEAR (ESP DIRECTIONAL) WILL LIKELY
MAINTAIN PROGRESSIVE LINEAR SEGMENTS/QLCS, HOWEVER GIVEN THE DEGREE
OF INSTABILITY AND TPW, SUB-HOURLY RAINFALL RATES OF 2-3 INCHES
WILL BE POSSIBLE UNDERNEATH THE STRONGEST CELLS.
HURLEY
..SOUTHEAST TO MID ATLANTIC TO OHIO VALLEY
..0100 UTC UPDATE
WEAK MID-LEVEL LAPSE RATES (<6.5 C/KM PER SPC MESOANALYSIS) IS
LEADING TO A INCREASING LOWER-LAYER STABILITY ACROSS MUCH OF THIS
REGION FOLLOWING SUNSET. MUCAPES STILL 1500-3000 J/KG OVER MUCH OF
THE AREA IS STILL SUFFICIENT FOR AREAS OF HEAVY RAINFALL,
ESPECIALLY CONSIDERING THE OVERALL WEAK FLOW (SOUTHERLY CORFIDI
VECTORS 5-10 KTS) AND PWATS BETWEEN 1.7-2.0+ INCHES OVER MOST
AREAS. HOWEVER THE AREA(S) OF CONVECTIVE CLUSTERS WITHIN AN OVERALL
DIFFUSE WARM CONVEYOR BELT (WCB) ARE RATHER DISORGANIZED, AND AS WE
CONTINUE TO PROGRESS FARTHER BEYOND PEAK DIURNAL HEATING, EXPECT
ANY SHORT-TERM RUNOFF ISSUES TO BE MORE LOCALIZED/ISOLATED. AS A
RESULT, ALL SLIGHT RISK AREAS WERE REMOVED.
HURLEY
..NORTHERN ROCKIES
16Z UPDATE... CONVECTION THIS MORNING HAS BEEN FIRING UP ACROSS
EASTERN WASHINGTON AND NORTHERN IDAHO, AREAS VERY SIMILAR IN
TOPOGRAPHY WITH SENSITIVE LOCATIONS AS DESCRIBED BELOW. THE WESTERN
BOUNDARY OF THE MARGINAL RISK WAS EXPANDED INTO EASTERN WASHINGTON
TO COVER THIS CONVECTION AND MORE EXPECTED LATER IN THE DAY.
CAMPBELL
ENERGETIC DISTURBANCE EJECTING OUT OF THE PACIFIC NORTHWEST AND
BRITISH COLUMBIA WILL MAKE HEADWAY INTO THE NORTHERN ROCKIES BY
LATER THIS AFTERNOON LEADING TO A PERIOD OF CONVECTIVE ACTIVITY TO
SPAWN ALONG THE LEWIS RANGE DOWN INTO THE HIGH VALLEYS OF WESTERN
MT. PWATS RUNNING OVER 1" ACROSS THE NORTHERN ROCKIES IS WELL ABOVE
CLIMO NORMS, CLOSER TO THE 99TH PERCENTILE AS NOTED BY THE LATEST
NAEFS OUTPUTS, MORE THAN SUFFICIENT TO BE A PROBLEM FOR ANY MORE
SENSITIVE TOPOGRAPHIC FEATURES PRESENT GIVEN THE COMPLEX
TOPOGRAPHY. MULTIPLE BURN SCARS IN THE AREA WILL ALSO BE UNDER
THREAT FOR SEEING RAINFALL RATES BETWEEN 0.5-1"/HR AT TIMES, A
THRESHOLD THAT COULD CAUSE RAPID RUN OFF AND DEBRIS FLOWS IF CELLS
LINGER OVER THE SENSITIVE AREAS. THIS IS NOT A WIDESPREAD FLASH
FLOOD PROSPECT, BUT ISOLATED TO WIDELY SCATTERED INSTANCES CANNOT
BE RULED OUT CONSIDERING THE ABOVE ENVIRONMENT. A MRGL RISK REMAINS
IN PLACE TO ACCOUNT FOR THE LOWER END THREAT.
KLEEBAUER
DAY 2
VALID 12Z WED MAY 27 2026 - 12Z THU MAY 28 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE EASTERN
HALF OF TEXAS, PORTIONS OF THE LOWER MISSISSIPPI VALLEY, AND AREAS
OF THE OHIO VALLEY TO CENTRAL APPALACHIANS...
21Z UPDATE... A NEW MARGINAL RISK AREA WAS RAISED FOR EASTERN
WASHINGTON, NORTHERN IDAHO AND WESTERN MONTANA. DEEP MOISTURE OVER
THE REGION MAINTAINING ABOVE CLIMO PW VALUES FOR LATE MAY. A WAVE
MAKING ITS WAY THROUGH THE REGION ALONG WITH DIFFERENTIAL HEATING
WILL HELP TRIGGER CONVECTION CAPABLE OF RAIN RATES UPWARDS OF 0.50
TO 1+ INCHES/HR IN ISOLATED AREAS. THESE RATES, IF FALLING OVER
RECENT BURN SCARS AND OTHER SENSITIVE LOCATIONS HAVE THE POTENTIAL
TO CAUSE ISOLATED FLASH FLOODING AND/OR DEBRIS FLOWS IN STEEP
TERRAIN. HOWEVER A LIMITING FACTOR WILL BE THAT THE AREAL COVERAGE
OF THUNDER WILL BE LESS THAN THAT OF THE DAY 1 PERIOD.
CAMPBELL
..TEXAS TO LOWER MISSISSIPPI VALLEY
THE BROAD UPPER LEVEL EVOLUTION OCCURRING UPSTREAM OVER THE
SOUTHERN PLAINS WILL CONTINUE TO SHIFT EAST WITH THE LARGE SCALE
FORCING DRIVING INTO THE EASTERN HALF OF TX LEADING TO HEAVY RAIN
PROSPECTS OVER THE EASTERN PORTIONS OF HILL COUNTRY, THE I-35
CORRIDOR AND MUCH OF EAST TX, INCLUDING THE MIDDLE AND UPPER TX
COASTAL AREAS ON WEDNESDAY. ENVIRONMENTAL CONDITIONS FOR HEAVY
RAINFALL ARE MOST FAVORABLE ALONG THE TX AND LA GULF COAST AREAS
WITH A CORRIDOR OF ELEVATED THETA_E'S ALIGNED FROM CORPUS CHRISTI
UP THROUGH THE LOWER SABINE TO ABOUT 100 MILES INLAND. THE SETUP IS
CONTINGENT ON THE BEHAVIOR OF THE CONVECTIVE PATTERN UPSTREAM INTO
THE CENTRAL PORTION OF THE STATE AND THE MIGRATION OF THE
THUNDERSTORM COMPLEX EXITING OUT OF I-35. THE GENERAL CONSENSUS IS
THE MAXIMA FOR PRECIP WILL LIKELY OCCUR IN PROXIMITY TO THE SAME
AREAS THAT WERE HIT WITHIN THE PAST WEEK; THE AREA ALONG THE UPPER
TX COAST FROM HOUSTON UP TO LAKE CHARLES. THIS IS VERY WELL DEFINED
WITHIN THE PROBABILITY FIELDS IN BOTH THE HREF AND THE AIFS-ENS
WHERE >3" IS LIKELY (60-90%) WITHIN THE CONFINES OF THAT ZONE WITH
THE HREF EVEN SIGNALING MODEST >5" POTENTIAL (40-60%) IN THAT SAME
ZONE. THERE'S STILL SOME UNCERTAINTY IN THE BEHAVIOR OF ANY
MESOSCALE COMPLEXES THAT END UP MATERIALIZING FROM ALL THE
CONVECTIVE DEVELOPMENT THE PREVIOUS EVENING AND IF THEY CAUSE ANY
SIGNIFICANT SHIFTS IN THE POTENTIAL. IN THIS CASE, THIS LEADS TO A
BROAD SLGT RISK WITH A MRGL RISK ENCOMPASSING OVER THE SOUTHERN
PLAINS TO LOWER MISSISSIPPI VALLEY AS BROAD UPPER FORCING WILL
LIKELY SPUR SCATTERED CONVECTION ALL ACROSS AREAS FROM WESTERN KS
DOWN THROUGH OK IN THE SETUP. AREAS AWAY FROM EAST TX AND THE LOWER
MISSISSIPPI WILL HAVE MORE ISOLATED HEAVY RAIN PROSPECTS,
COMPARATIVELY, SO THE THREAT REMAINS ELEVATED IN THE SLGT RISK
WITHIN THESE PARTICULAR LOCATIONS.
..OHIO VALLEY
21Z UPDATE... A MINOR WESTWARD NUDGE WAS MADE ACROSS INDIANA ALONG
WITH A SOUTH AND EAST EXPANSION ACROSS WEST VIRGINIA TO ACCOUNT FOR
THE LATEST MODEL TRENDS AND WPC QPF.
CAMPBELL
CONDITIONS WILL BECOME INCREASINGLY FAVORABLE FOR HEAVY RAINFALL
ACROSS THE OHIO VALLEY GOING INTO WEDNESDAY FROM A MULTITUDE OF
FEATURES THAT WILL ULTIMATELY COUPLE INTO SOMETHING MORE FORMIDABLE
DURING PEAK DIURNAL INSTABILITY. SHEARED VORTICITY STEMMING FROM
PREVIOUS PERIOD CONVECTION WILL LIKELY SETTLE OVER THE CENTRAL OHIO
VALLEY WITH A WEST TO EAST BISECTING QUASI-STATIONARY FRONT
POSITIONED JUST NORTH OF THE OHIO RIVER BASIN. A SWEEPING TROUGH
EXITING OUT OF ONTARIO WILL HELP TIGHTEN AN AXIS OF CONFLUENCE
ACROSS THE MIDWEST AND OHIO VALLEY BY WEDNESDAY AFTERNOON, ENTICING
A SQUEEZE OF THE THERMAL GRADIENT AND REGIONAL INSTABILITY AXIS
THAT ALIGNS WITH THE FRONTAL PLACEMENT. DESTABILIZATION BY THE
AFTERNOON HOURS WILL LEAD TO SCATTERED TO WIDESPREAD THUNDERSTORM
INITIATION ALONG THE BOUNDARY WITH CONVECTIVE EPISODES LIKELY TO
SPAWN HEAVIER CELLS CAPABLE OF HOURLY RATES BETWEEN 1-2"/HR AS PWAT
ANOMALIES SIT FIRMLY WITHIN +2 STANDARD DEVIATIONS ABOVE CLIMO.
PREVIOUS PERIODS OF RAINFALL IN THE LAST THREE TO FOUR DAYS HAVE
REALLY BROUGHT DOWN THE AREAL FFG MARKERS FOR ALL 1/3/6 HOUR
THRESHOLDS WITH A VAST MAJORITY OF PLACES ALONG THE OHIO RIVER
BASIN AND POINTS NORTH RUNNING <1"/HR IN THE HOURLY EXCEEDANCE
INDICATOR. THIS POINTS TO ANY HEAVIER CONVECTIVE IMPACTS COULD
CAUSE ISSUES WITH THE REMNANT SOIL MOISTURE AND HYDROLOGIC
CONCERNS THAT ARE LINGERING AFTER THE LAST EVENT. THIS IS
ESPECIALLY TRUE FOR EASTERN OH, SOUTHWEST PA, AND WESTERN WV WHERE
COMPLEX TOPOGRAPHY ONLY EXACERBATE THE POTENTIAL IN THESE ZONES.
3-HOUR FFG EXCEEDANCE PROBABILITIES FROM THE 00Z HREF ARE BETWEEN
20-40% FOR A LARGE PORTION OF EASTERN IN THROUGH THE SOUTHERN HALF
OF OH INTO SOUTHWEST PA WITH A MAXIMA OF 40-60% LOCATED ACROSS
NORTHWEST WV BETWEEN US50 AND WV7. CONSIDERING THE ANTECEDENT
CONDITIONS AND EXPECTED WIDESPREAD CONVECTIVE REGIME ALONG THE
FRONT, A SLGT RISK WAS ADDED FOR AN INCREASING THREAT FOR FLASH
FLOODING WEDNESDAY.
KLEEBAUER
DAY 3
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, NORTHERN ROCKIES, LOWER
MISSISSIPPI VALLEY, AND SOUTHEAST FLORIDA...
21Z UPDATE... A NEW MARGINAL RISK AREA WAS RAISED FOR EASTERN
WASHINGTON, NORTHERN IDAHO AND WESTERN MONTANA TO CARRY ON THE
ELEVATED THREAT POTENTIAL DESCRIBED IN THE DAY 1 AND DAY 2 PERIODS. A
MINOR WESTWARD EXPANSION OF THE MARGINAL RISK WAS MADE FOR PALM
BEACH COUNTY TO ACCOUNT FOR TRENDS AND THE NEW WPC QPF, ELSEWHERE
REMAINS IN GOOD ORDER.
CAMPBELL
..PLAINS TO LOWER MISSISSIPPI VALLEY
BREAKDOWN OF THE PERSISTENT PATTERN FOR AREAS EAST OF THE
CONTINENTAL DIVIDE WILL LEAD TO WEAKER STEERING FLOW, BUT STILL
ENOUGH MOISTURE, LINGERING BOUNDARIES, AND REMNANT MID-LEVEL
VORTICITY TO SPUR UP BOUTS OF SCATTERED CONVECTION ALL ACROSS PARTS
OF THE CENTRAL AND SOUTHERN PLAINS INTO THE MISSISSIPPI VALLEY.
THIS SETUP IS A FAR CRY FROM WHAT WE'VE EXPERIENCED THE PAST
SEVERAL DAYS, SO THE PROSPECTS OF WIDESPREAD FLASH FLOODING ARE
MUCH LOWER COMPARATIVELY. HOWEVER, ENVIRONMENTAL CONDITIONS AND
DEEP MOISTURE PRESENCE STILL REMAIN FAVORABLE ALONG THE NORTHERN
PERIPHERY OF THE TROUGH LINGERING ACROSS EAST TX WHICH PLACES THE
BEST OPPORTUNITY FOR CONVECTIVE EPISODES TO BE LOCATED OVER THE
AFOREMENTIONED AREAS. ENSEMBLE QPF FOOTPRINT IS MOST NOTABLE ACROSS
THE CENTRAL GULF COAST AND UPPER TX COASTAL PLAIN, LIKELY IN PART
TO THE POSITIONING OF THE TROUGH AND THE FACT THE MOST PREVALENT
THETA_E IS SITUATED ALONG THE IMMEDIATE GULF. IT'S A PERIOD TO
MONITOR FOR ANY SMALL SCALE FEATURES THAT COULD ENHANCE CONVECTIVE
POTENTIAL FURTHER, BUT FOR NOW, A BROAD MRGL EXISTS TO COVER FOR
THE THREAT.
..FLORIDA
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. GLOBALS AND REGIONAL
GUIDANCE EVEN HAVE SOME 2+" TOTALS ALREADY IN THE OUTPUT, AND
THAT'S BEFORE THE CAM'S EVEN HAVE A DEPICTION. TYPICALLY, THIS IS A
SIGN FOR HEAVY RAINFALL PROSPECTS CAPABLE OF FLASH FLOODING,
ESPECIALLY WHEN YOU CONSIDER THE PWATS RUNNING +1 TO +2 DEVIATIONS
ACROSS THAT AREA OF THE PENINSULA. A MRGL RISK REMAINS FOR THAT
URBAN CORRIDOR OF SOUTHEASTERN FL.
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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