796
FOUS30 KWBC 292021
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
421 PM EDT TUE APR 29 2025
DAY 1
VALID 16Z TUE APR 29 2025 - 12Z WED APR 30 2025
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHERN PLAINS...
..SOUTHERN PLAINS
16Z UPDATE: NO MAJOR CHANGE TO THE REASONING OUTLINED BELOW, BUT
THERE WAS AN OVERALL TREND TO SHIFT RISK AREAS SOUTHWARD A BIT.
ALTHOUGH HI-RES MODELS (EVEN THE VERY RECENT 12Z RUNS) ARE
STRUGGLING TO CAPTURE ONGOING CONVECTION IN THE REGION, THEY ALL DO
CONSISTENTLY SHOW ORGANIZED CONVECTION THIS AFTERNOON AND EVENING
GENERATING FAIRLY STRONG COLD POOLS, WHICH IN TURN GRADUALLY PUSHES
THE EFFECTIVE FRONT SOUTH INTO N TX BY THIS EVENING AND OVERNIGHT.
THIS IS SUPPORTED BY RAP ANALYSIS SHOWING HIGHER DCAPE VALUES
ACROSS PORTIONS OF N TX, AS WELL AS THE 12Z FWD SOUNDING WHICH
REVEALED A LAYER OF FAIRLY DRY AIR JUST ABOVE THE BOUNDARY LAYER.
OF THE AVAILABLE HI-RES MODELS, RECENT RUNS OF THE RRFS SEEM TO
BEST REPRESENT THE FORWARD PROPAGATING BOW ECHO IN S MO AND
ADDITIONAL DEVELOPMENT IN SW OK. THEREFORE, THE TWEAKS TO THE
POSITIONING OF THE RISK AREAS LEVERAGED THE RRFS A BIT MORE,
ALTHOUGH SOME DEFERENCE WAS GIVEN TO OTHER GUIDANCE SOURCES AS
WELL. EVEN MODELS THAT AREN'T HANDLING ONGOING CONVECTION VERY WELL
STILL INDICATE THE DEVELOPMENT OF COLD POOLS, AND THE TENDENCY FOR
THE AXIS OF ACTIVE CONVECTION TO SINK SOUTH WITH TIME. THIS LENDS
SOME CONFIDENCE TO THE OVERALL EXPECTATIONS DESCRIBED HERE. THE
SOUTHWARD PROGRESSION OF THE EFFECTIVE FRONT SEEMS TO STALL
OVERNIGHT, WHICH MAY LEAD TO A RAINFALL MAX IN N TX, OR AT LEAST
VERY CLOSE TO THE RED RIVER.
PREVIOUS DISCUSSION: A REPETITIVE SCHEME OF SUCCESSIVE CONVECTIVE
OUTPUTS ACROSS PORTIONS OF WEST TX THROUGH OKLAHOMA WILL RESULT IN
SIGNIFICANT FLASH FLOODING FOR A LARGE PORTION OF THE ABOVE AREAS.
THE COMBINATION OF SEVERAL MID-LEVEL IMPULSES EJECTING NORTHEAST
WITHIN A LARGE SCALE DIFFLUENT PATTERN WILL INTERACT WITH A QUASI-
STATIONARY FRONT ALIGNED FROM THE WESTERN ROLLING PLAINS OF TX UP
TOWARDS THE RED RIVER BASIN MAINLY WEST OF I-35. FAVORABLE MID-
LEVEL ASCENT WILL ALLOW FOR WAVES OF CONVECTIVE INITIATION
BEGINNING LATE-MORNING AND AFTERNOON TUESDAY WITH A SECONDARY PULSE
AROUND 00Z WEDNESDAY WITH A FINAL PULSE FORECAST AFTER 06Z AS THE
MEAN TROUGH FINALLY STARTS PIVOTING EAST OUT OF THE SOUTHWESTERN
CONUS. INSTABILITY WITHIN THE CONFINES OF WEST TX UP TO THE RED
RIVER WILL ALLOW FOR RAPID DEVELOPMENT OF CONVECTIVE CLUSTERS WITH
SOME SUPERCELLULAR MODES PLAUSIBLE PRIOR TO NIGHTFALL, EVENTUALLY
MERGING INTO A MORE MULTI-CELLULAR SCHEME WITH BACKBUILDING FAVORED
WITHIN THE CONFINES OF THE FRONT DENOTED PRETTY WELL WITHIN THE
THETA_E GRADIENT OUTPUT IN EACH DETERMINISTIC. ALL CAMS ARE WELL
SUPPORTIVE OF THE 3-WAVE CONVECTIVE EVOLUTION WITH HEAVY RAINFALL
SITUATED ACROSS THE SOUTHERN HIGH PLAINS NEAR THE EASTERN PERMIAN
BASIN WITH A GENERAL QPF MAXIMA ALIGNED SOUTHWEST TO NORTHEAST
ACROSS THE NORTHERN EXTENSION OF THE ROLLING PLAINS IN TX, UP
THROUGH THE RED RIVER AND INTO THE SOUTHERN PORTION OF THE OKC
METRO. THIS AREA HAS BEEN THE BENEFACTOR OF MULTIPLE CONVECTIVE
EPISODES ALREADY, LEADING TO FLASH FLOODING WITHIN THE CORRIDOR
EXTENDING FROM LAWTON DOWN TO THE RED RIVER. THIS AREA WILL BE THE
MOST PRIMED LOCATION FOR NOT ONLY WIDESPREAD FLASH FLOODING, BUT
SIGNIFICANT LIFE-THREATENING FLASH FLOOD PROSPECTS DUE TO THE WELL
ABOVE NORMAL SOIL MOISTURE ANOMALIES LIKELY CURBING ANY POTENTIAL
FOR RAINFALL TO SOAK INTO THE TOP SOIL LAYER.
LATEST 00Z HREF PROBABILITY FIELDS ARE OVERWHELMINGLY INDICATIVE OF
THE THREAT WITH ONE OF THE MORE ROBUST INDICATIONS OCCURRING
WITHIN THE 6-HR FFG EXCEEDANCE PROBABILITY MARKER RUNNING BETWEEN
70-90% ACROSS THE AREA EXTENDING FROM FOARD COUNTY IN TX UP TO
WESTERN CLEVELAND COUNTY IN OK. NEIGHBORHOOD PROBABILITIES OF >5"
TOTAL RAINFALL ARE RUNNING BETWEEN 50-80% IN THE SAME LOCATION WITH
>8" BETWEEN 20-30% ACROSS SOUTHWEST OK BETWEEN LAWTON TO THE RED
RIVER. NEIGHBORHOOD PROBS FOR >3" ARE SIGNIFICANT ACROSS MUCH OF OK
BACK INTO NORTH TX WITH THE SOUTHWEST EXTENSION BACK INTO THE
SOUTHEAST CORNER OF THE LUB CWA. CONSIDERING THE NASA SPORT SOIL
MOISTURE PERCENTILES RUNNING BETWEEN 70-99% FOR THE 0-40CM LAYER
ACROSS THE ENTIRE AREA ABOVE, THE PROPENSITY FOR FLOODING, EVEN IN
RURAL ZONES WILL BE HIGHER THAN NORMAL. GIVEN EXPECTED RATES
BETWEEN 1-2"/HR DURING PEAK STORM CYCLES AND THE EXPECTATION FOR
>3" OF RAINFALL...THE THREAT WILL BE OF THE HIGHER MAGNITUDE IN
TERMS OF IMPACT PROSPECTS. THE PREVIOUS MDT RISK INHERITED WAS NOT
ONLY MAINTAINED, BUT EXPANDED A BIT FURTHER SOUTHWEST TO ALIGN WITH
THE HIGHER PROBABILITIES WITH THE NEIGHBORHOOD >5" POTENTIAL AND
THE ELEVATED HREF EAS >2" PROBABILITIES THAT HAVE BEEN DEPICTED. A
HIGH-END MDT RISK IS FORECAST ACROSS THE RED RIVER BASIN WEST OF
WICHITA FALLS UP INTO THE SOUTHERN FRINGES OF THE OKC METRO,
INCLUDING THE TOWN OF NORMAN. LOWER END PROBABILITIES FOR FLASH
FLOODING WILL EXIST ACROSS AREAS OF THE EASTERN PERMIAN BASIN OUT
THROUGH THE CONCHO VALLEY AS WELL AS ACROSS MUCH OF OKLAHOMA NOT
INCLUDED IN THE MDT.
..MISSISSIPPI AND OHIO VALLEYS
16Z UPDATE: NO MAJOR CHANGES WERE MADE TO THE RISK AREAS HERE.
PREVIOUS DISCUSSION: MID-LEVEL IMPULSES THAT EJECT OUT OF THE
SOUTHERN PLAINS WILL CONTINUE TO PRESS NORTHEAST TOWARDS THE
MISSISSIPPI AND OHIO VALLEYS WITH A PROGRESSIVE COLD FRONT MOVING
SOUTHEAST OUT OF THE MIDWEST DURING THE SAME TIME FRAME. AFTERNOON
DESTABILIZATION COUPLED WITH THE FAVORABLE ADDITION OF MID-LEVEL
FORCING AND SURFACE FRONTOGENESIS WILL LEAD TO SCATTERED CONVECTIVE
PULSES ACROSS THE REGION WITH SOME ORGANIZED ELEMENTS FOCUSED
WITHIN THE CONFINES OF THE FRONT AND UNDER THE SHORTWAVE
PROPAGATION. SOILS REMAIN MOIST ACROSS MUCH OF THE REGION EXTENDING
FROM MO THROUGH THE OHIO RIVER BASIN WITH AN EASTERN EXTENSION TO
THE CENTRAL APPALACHIANS AND WESTERN PA HIGHLANDS. PWAT ANOMALIES
ON THE ORDER OF +1 TO AS HIGH AS +2.5 DEVIATIONS CEMENTS A
FAVORABLE DEEP MOIST ENVIRONMENT CONDUCIVE FOR HEAVY RAINFALL
PROSPECTS WITHIN ANY CONVECTIVE SCHEME. THE GREATEST CONCENTRATION
OF HEAVY RAIN WILL LIKELY BE BACK OVER SOUTHERN AND CENTRAL MO
TOWARDS THE 3 RIVER CONFLUENCE ZONE NEAR KY/MO/IN/IL. HREF PROBS
FOR >1" ARE VERY HIGH (70-90+%) ACROSS MUCH OF THE MISSISSIPPI AND
OHIO VALLEY AREAS WITH >2" PROBS RELATIVELY HIGH (50-70%) IN-OF THE
OHIO RIVER BASIN OVER SOUTHERN IL THROUGH MUCH OF EASTERN KY. THE
COMBINATION OF CONVECTION OVER AREAS THAT ARE STILL IN RECOVERY
FROM PREVIOUS RAINFALL EPISODES AND COMPLEX TERRAIN WILL CREATE A
THREAT FOR ISOLATED TO PERHAPS SCATTERED FLASH FLOOD INSTANCES OVER
A LARGE AREA DURING THE AFTERNOON AND EVENING HOURS TUESDAY. A
SLGT RISK REMAINS FIRMLY IN PLACE ACROSS MUCH OF MO ALONG AND SOUTH
OF I-70 UNTIL THE 3 RIVER CONFLUENCE ZONE REFERENCED ABOVE. A MRGL
RISK ENCOMPASSES ALL OTHER AREAS EAST THROUGH WESTERN PA AND EVEN
THE SOUTHWEST CORNER OF NY STATE.
LAMERS/KLEEBAUER
DAY 2
VALID 12Z WED APR 30 2025 - 12Z THU MAY 01 2025
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTH-CENTRAL AND SOUTHEAST OKLAHOMA, NORTH TEXAS, AND WESTERN
ARKANSAS...
THE PRIMARY CHANGE FOR THIS UPDATED ERO FOR WEDNESDAY WAS TO
RECENTER THE MODERATE RISK FURTHER SOUTH (APPROX. 50 MI). THIS WAS
DUE TO A CORRESPONDING SHIFT IN GUIDANCE, ESPECIALLY HI-RES
GUIDANCE, BUT ALSO THE UKMET, CMC, AND ECMWF AIFS. IT ALSO FITS
WITH THE UPDATED EXPECTATIONS FOR THE CURRENT DAY 1 PERIOD, AS
GUIDANCE HAS SIGNALED THE POTENTIAL FOR RELATIVELY STRONG COLD
POOLS REINFORCING THE EFFECTIVE FRONT AND GRADUALLY PUSHING IT
FURTHER SOUTH. THIS WOULD CENTER IT MORE SQUARELY NEAR THE RED
RIVER (OK-TX BORDER REGION) OR PERHAPS FULLY INTO N TX. THERE IS
STILL SOME UNCERTAINTY ASSOCIATED WITH THE EXACT CONVECTIVE
EVOLUTION OVER THE 12-18 HOURS IMMEDIATELY PRIOR TO THE START OF
THE DAY 2 PERIOD, SO THE MODERATE RISK AND SLIGHT RISK WERE KEPT
FAIRLY BROAD TO ACCOUNT FOR DIFFERENT SCENARIOS. NEVERTHELESS,
THERE WAS A CLEAR ENOUGH SHIFT IN THE GUIDANCE TO WARRANT AN
ADJUSTMENT IN THE OVERALL RISK CONTOURS.
A SIGNIFICANT FLASH FLOODING EVENT COULD BE ONGOING AT THE START OF
THE PERIOD (~12Z WEDNESDAY) OVER WESTERN NORTH TEXAS AND/OR SOUTH-
CENTRAL AND SOUTHWEST OKLAHOMA. LATE TONIGHT THE SOUTHWARD DRIFT OF
THE EFFECTIVE FRONT AND THE ASSOCIATED ZONE OF ACTIVE CONVECTION
MAY BEGIN TO SLOW OR STALL AS THE LOW-LEVEL JET (LLJ) BEGINS TO
RAMP UP CONSIDERABLY OVER TEXAS. WHERE THE NOSE OF THE LLJ SETS UP
RELATIVE TO ONGOING CONVECTION WILL GO A LONG WAY TO DETERMINING
THE PRIMARY AREA OF CONCERN FOR WEDNESDAY. MOST HI-RES MODELS SHOW
THE CONVECTIVE CLUSTER(S) PROPAGATING EAST THROUGH THE MORNING
TOWARD AR AND N LA, WITH RENEWED DEVELOPMENT UPSTREAM OVER N TX BY
THE AFTERNOON AND ANOTHER TRAINING AND BACKBUILDING CONFIGURATION.
THIS SAME GUIDANCE GENERALLY SUPPORTS THE IDEA OF A 24-HOUR
RAINFALL MAXIMUM IN EXCESS OF 7 INCHES SOMEWHERE IN THE NEW
MODERATE RISK AREA, BUT THERE IS LINGERING UNCERTAINTY AS TO
PRECISELY WHERE THAT WILL OCCUR. ALTHOUGH THE PROBABILITY IS
CURRENTLY HIGHEST IN THE VICINITY OF THE RED RIVER NEAR WHERE SE OK
BORDERS N TX, IT'S CONCEIVABLE IT COULD OCCUR CLOSER TO OR INSIDE
THE DFW METRO AREA. THE METRO AREA IS NOW FULLY IN THE MODERATE
RISK AREA WITH THIS LATEST UPDATE.
SOME SIGNIFICANT FLASH FLOODING WILL BE POSSIBLE AS MUCH OF THE
RAIN WILL LIKELY FALL IN 6-12 HOURS AND THE HIGH END AMOUNTS
PRODUCED BY SOME OF THE GUIDANCE WOULD APPROACH OR EXCEED A 100
YEAR ARI FOR THOSE DURATIONS. NEIGHBORHOOD PROBABILITIES OF
100 YEAR ARI EXCEEDANCE ARE NOT PARTICULARLY HIGH, REFLECTING BOTH
THE UNCERTAINTY OF THE EXACT PLACEMENT OF THE HEAVIEST AMOUNTS, AND
THAT AMOUNTS WELL IN EXCESS OF THOSE THRESHOLDS ARE NOT CURRENTLY
SUPPORTED BY GUIDANCE. SIGNIFICANT AND LIFE-THREATENING FLASH
FLOODING WOULD BE MOST LIKELY IN TWO SCENARIOS:
(1) IN WESTERN NORTH TEXAS OR SOUTH-CENTRAL OKLAHOMA AT THE
BEGINNING OF THE PERIOD, AS A CONTINUATION FROM THE PREVIOUS NIGHT.
THESE AREAS HAVE BEEN QUITE WET OVER THE PAST WEEK OR SO, SO THERE
IS EXISTING VULNERABILITY TO EXTREME RAINFALL. (THIS IS MORE
LIKELY.)
(2) IN THE DALLAS-FT. WORTH METRO AREA, AS THE RAINFALL IN QUESTION
WOULD CAUSE SERIOUS ISSUES IN A HIGHLY URBANIZED AREA. (THIS IS
ALSO POSSIBLE, BUT NOT CERTAIN, AND HIGHLY DEPENDENT ON THE EXACT
CONVECTIVE EVOLUTION.)
FURTHER NORTH, A BROAD MARGINAL AND SLIGHT RISK AREA WAS MAINTAINED
FOR THE MID MISSISSIPPI VALLEY AND CENTRAL PLAINS. THERE IS SOME
SIGNAL FOR ORGANIZED CONVECTION AND LOCALIZED HEAVY RAINFALL,
INCLUDING A SCATTERING OF LOW PROBABILITIES OF FFG EXCEEDANCE, BUT
CONFIDENCE IN ANY SPECIFIC SCENARIO IS LACKING.
LAMERS
DAY 3
VALID 12Z THU MAY 01 2025 - 12Z FRI MAY 02 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER A BROAD AREA
FROM THE GREAT LAKES TO MID MISSISSIPPI VALLEY TO WESTERN GULF
COAST...
AN EXPANSIVE PLUME OF INSTABILITY IS EXPECTED TO SUPPORT SCATTERED
TO NUMEROUS AREAS OF THUNDERSTORMS DURING THE DAY 3 PERIOD AHEAD OF
A SURFACE LOW AND TRAILING COLD FRONT. MACHINE LEARNING
PROBABILITIES FROM COLORADO STATE SUPPORT THE IDEA OF A BROAD
MARGINAL RISK; THIS IS WHAT WAS INHERITED AND IT WAS GENERALLY
MAINTAINED. THE BIGGEST CHANGE WAS TO EXTEND THE AREA SOUTHWEST
THROUGH PORTIONS OF LOUISIANA AND SOUTH AND SOUTHEAST TEXAS.
CONFIDENCE IN SPECIFICS IS LOW, AND THE OVERALL FLASH FLOOD THREAT
SHOULD BE LIMITED BY THE FAIRLY PROGRESSIVE NATURE OF THE
CONVECTION. PRECIPITABLE WATER VALUES ARE MORE ANOMALOUS IN THE
GREAT LAKES REGION (ABOVE THE 90TH PERCENTILE; ABOVE 1.3 INCHES),
BUT THAT IS ALSO WHERE THUNDERSTORMS SHOULD BE MOVING THE FASTEST.
MEANWHILE, AVAILABLE MOISTURE WILL BE LESS ANOMALOUS FURTHER SOUTH,
IN TX AND LA, BUT THUNDERSTORMS WILL BE MOVING SLOWER. THEREFORE,
HEAVY RAINFALL INGREDIENTS WILL GENERALLY BE OFFSET ACROSS THE
WHOLE REGION. HI-RES MODELS THAT EXTEND OUT BEYOND 48 HOURS SHOW
MORE SIGNIFICANT LOCALIZED RAINFALL MAXIMA IN TX AND LA, WHICH
MAKES SENSE GIVEN STRONGER INSTABILITY AND SLOWER OVERALL STORM
MOTIONS. THIS MAY BE WHERE A TARGETED UPGRADE TO A SLIGHT RISK IS
EVENTUALLY NEEDED.
LAMERS
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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