937
FOUS30 KWBC 151948
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
348 PM EDT WED APR 15 2026
DAY 1
VALID 16Z WED APR 15 2026 - 12Z THU APR 16 2026
...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR THE GREAT
LAKES AND NORTHERN OHIO VALLEY..
..GREAT LAKES AND OHIO VALLEY
16Z UPDATE: ANOTHER ROUND OF CONVECTION ANTICIPATED THIS AFTERNOON
AND EVENING WITH THE RELATIVE QPF MAXIMA LIKELY OCCURRING OVER
SIMILAR AREAS THAT WERE IMPACTED THE PAST 24 HRS. ANTECEDENT
CONDITIONS FAVOR A MORE SENSITIVE SOIL MOISTURE COMPOSITION ALONG
WITH REMNANT ELEVATED STREAMFLOWS SITUATED ACROSS THE AREA FROM
EASTERN IA THROUGH NORTHERN IL AND SOUTHERN WI. THIS ZONE OVER INTO
LOWER MI IS THE MOST SENSITIVE REGION FOR THE PERIOD IN QUESTION
LEADING TO A BIT MORE OF A PROACTIVE APPROACH IN THE FORECAST SLGT
RISK. THE INHERITED RISK WAS EXPANDED A BIT FURTHER NORTH ACROSS
THE AFOREMENTIONED AREAS, ENCOMPASSING NOW ALL OF SOUTHERN WI AND
NORTHERN IL AS THE NEXT WAVE OF CONVECTION WILL LIKELY REFIRE IN
PROXIMITY TO THE QUASI-STATIONARY FRONT AND POINT SOUTH WHERE
INSTABILITY IS GREATEST ALONG WITH A ROBUST PWAT ANOMALY (95-99TH
PERCENTILE) GIVEN SEASONAL CLIMATOLOGY. KDTX PWAT'S WERE A PRIMARY
SIGNAL FOR THIS CHARACTERISTIC THIS MORNING AS THEIR 1.14" PWATS
CAME IN SQUARELY AROUND A +3 DEVIATION FOR THE DATE, AND THIS AREA
ISN'T EVEN IN THE MORE ROBUST MOISTURE ANOMALY WHEN ASSESSING THE
THE LATEST NAEFS WHERE FURTHER SOUTHWEST IS EVEN MORE APPRECIABLE
IN ITS ANOMALY.
12Z HREF BLENDED MEAN QPF DEPICTS A RELATIVELY SOLID 1-2"
DISTRIBUTION WITH EMBEDDED MAXIMA BETWEEN 2-2.5" ACROSS THE
SOUTHERN WI TO NORTHERN IL AREA WITH A SECONDARY MAXIMA ORIENTED
FROM WEST-CENTRAL IL UP INTO SOUTHEAST MI, BISECTING NORTHERN IN IN
THE PROCESS. NEIGHBORHOOD PROBABILITIES OF >2" ARE UPWARDS OF
50-80% WITHIN THE TWO ZONES REFERENCED WITH A GENERAL MIN AROUND
THE CHICAGO METRO. CONSIDERING THE NATURE OF CONVECTION AND HOW
SMALL DEVIATIONS IN OUTFLOW PROPAGATION CAN PLAY BIG PARTS IN THE
FORECAST, FELT IT WAS NECESSARY TO MAINTAIN THE MAJOR URBAN
CORRIDOR OF CHICAGO TO COVER FOR ANY UNCERTAINTY IN HOW THE
CONVECTIVE SCHEME WILL PLAY OUT THIS EVENING. THE SLGT RISK WAS
EXPANDED FURTHER SOUTHWEST INTO IL TO ACCOUNT FOR THE TRENDS IN
CAMS AND WITH COORDINATION FROM THE SPRINGFIELD, IL WFO WHERE
CONVECTION IS ALREADY CAUSING SOME 1-2" MAXIMA TO CROP UP PRIOR TO
THE UPDATE.
KLEEBAUER
..SOUTHERN PLAINS, ARKLATEX TO OZARKS
16Z UPDATE: CONVECTION WILL REFIRE ALONG THE DRYLINE AGAIN LATER
THIS AFTERNOON WITH UPSCALE GROWTH ANTICIPATED AFTER 00Z AS LLJ
INTRODUCTION WILL AID IN MULTI-CELL MERGERS AND HEAVY RAIN
PROSPECTS FROM SOUTHERN MO DOWN INTO NORTH TX. UPPER PATTERN TO THE
WEST REMAINS FAVORABLE FOR LARGE SCALE ASCENT TO OCCUR ACROSS THE
RED RIVER BASIN OF TX/OK, PERHAPS AS FAR SOUTH AS THE I-20
CORRIDOR, TO POINTS NORTHEAST WITHIN EASTERN OK AND NEIGHBORING AR
TO SOUTHERN MO AS THE ENTIRE REGION SETTLES WITHIN A DEVELOPING JET
COUPLET ON THE SOUTHERN EDGE OF A ROBUST SHORTWAVE TROUGH.
INSTABILITY AND DEEP MOISTURE PRESENCE SITUATED ACROSS ALL OF THE
SOUTHERN PLAINS TO MID-MISSISSIPPI VALLEY IS MORE THAN ENOUGH TO
CONSTITUTE GENERAL CONVECTIVE PROPERTIES WITH EFFICIENT RATES
BETWEEN 1-3"/HR AT PEAK INTENSITY, REPRESENTED VERY WELL BY THE
LATEST HREF HOURLY PROBABILITIES FOR >1"/HR RUNNING BETWEEN 25-60%
OVER THE ENTIRE AREA REFERENCED ABOVE WITH LOW-END TO MODEST PROBS
(15-30%) FOR >2"/HR IN A CORRIDOR BETWEEN NORTHWEST AR DOWN TO
SOUTHEASTERN OK. ANTECEDENT CONDITIONS IN THESE ZONES ARE STILL
PRETTY DRY WITH THE 1/3/6 HR FFG PARAMETERS ALL SUFFICIENTLY ABOVE
2.5" FOR EACH THRESHOLD. THAT SAID, URBANIZED AREAS WILL STILL SEE
HIGHER RUN OFF CAPABILITIES WITH A POTENTIAL FOR LOCALIZED FLASH
FLOODING IN THE EVENING AND OVERNIGHT TIME FRAME. THE OVERALL
METEOROLOGICAL PREMISE FOR A FLASH FLOODING THREAT REMAINS VIABLE,
BUT THE ANTECEDENT HYDROLOGIC CONCERNS ARE STILL RELATIVELY TAME
COMPARED TO AREAS MUCH FURTHER NORTH WHICH LEANS TOWARDS A
MAINTENANCE OF THE MRGL RISK INHERITED WITH A CHANCE ON A TARGETED
UPGRADE THIS EVENING PENDING CONVECTIVE OUTPUT.
KLEEBAUER
..NORTHEAST
16Z UPDATE: LITTLE CHANGE IN THE PREVIOUS FORECAST WITH A
WIDESPREAD MRGL RISK EXTENDING FROM WESTERN NY/PA OVER INTO PARTS
OF SOUTHERN NEW ENGLAND. HREF NEIGHBORHOOD PROBABILITIES ARE FAIRLY
ROBUST FOR >1" (50-80%) ACROSS MUCH OF THE ABOVE CORRIDOR WITH THE
HIGHEST PROBS FOR BOTH >1" AND >2" LOCATED DOWNWIND OF LAKE ERIE.
URBANIZED ZONES WILL BE THE PRIMARY AREAS OF INTEREST ACROSS THE
NORTHEAST U.S. WHICH HISTORICALLY HAS BEEN THE ROOT FOR MOST RUN
OFF POTENTIAL AND LOCALIZED FLASH FLOOD PROSPECTS. WITH GUIDANCE
MAINTAINING RUN-TO-RUN CONTINUITY, THIS WAS ENOUGH TO KEEP WHAT WAS
PREVIOUSLY FORECAST WITH ONLY SMALL MODIFICATIONS TO ALIGN WITH THE
LATEST HREF BLENDED MEAN QPF DISTRIBUTION.
KLEEBAUER
..PREVIOUS DISCUSSION..
REMNANTS OF THE STORMS ACROSS THE GREAT LAKES MAY BRING A ROUND OF
SHOWERS AND STORMS IN THE MORNING, FOLLOWED BY ANOTHER ROUND OF
HEAVIER SHOWERS AND THUNDERSTORMS IN THE AFTERNOON. MODEL GUIDANCE
SHOWS A CORRIDOR OF 1-1.5 INCHES RAINFALL WITH EMBEDDED HIGHER
AMOUNTS DEPENDING ON THE MODEL. THE RELATIVELY LOWER FLASH GUIDANCE
ACROSS WESTERN PENNSYLVANIA AND THE MORE URBAN FOOTPRINT OF AREAS
SUCH AS CONNECTICUT AND NEW ENGLAND ALSO HELP CONFIDENCE OF
EXPANDING THE MARGINAL EASTWARD.
CAMPBELL/WILDER
DAY 2
VALID 12Z THU APR 16 2026 - 12Z FRI APR 17 2026
THE PROBABILITY OF RAINFALL EXCEEDING FLASH FLOODING GUIDANCE IS
LESS THAN 5 PERCENT.
CAMPBELL/KLEEBAUER
DAY 3
VALID 12Z FRI APR 17 2026 - 12Z SAT APR 18 2026
...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE MID-MISSISSIPPI VALLEY INTO THE CENTRAL PLAINS...
20Z UPDATE: A DEEP, POSITIVELY-TILTED LONGWAVE TROUGH WILL WANDER
EASTWARD OUT OF THE ROCKIES ON FRIDAY LEADING TO BROAD LARGE SCALE
ASCENT FROM THE SOUTHERN PLAINS TO THE MIDWEST. A WELL-DEFINED AXIS
OF DIFFLUENCE AHEAD OF THE MEAN TROUGH WITH SEVERAL SHORTWAVES
RIPPING THROUGH THE FLOW WILL ENHANCE AN AREA OF CONVECTIVE
DEVELOPMENT WITHIN A STRENGTHENING WARM-SECTOR ENVIRONMENT
POSITIONED BETWEEN A STRONG COLD FRONT OVER THE HIGH PLAINS AND A
QUICKLY ADVANCING WARM FRONT MIGRATING POLEWARD THROUGH THE
ADJACENT MISSISSIPPI AND OHIO VALLEY'S. THE CURRENT SETUP IS
CONDUCIVE FOR A LARGE HEAVY RAIN FOOTPRINT WITH ENSEMBLE MEAN QPF
ALREADY DENOTING AN EXPANSIVE 1-2" OUTPUT WITH EMBEDDED HIGHER
TOTALS. THIS IS EVEN PRIOR TO THE CAMS ADDITIONS THAT HANDLE THE
MAGNITUDE OF CONVECTION BETTER, SO ANTICIPATING SOME 3+ INCH MEANS
LIKELY TO MATERIALIZE IN FUTURE UPDATES.
THE MAIN TREND THIS PERIOD IS THE CONTINUATION OF THE ML OUTPUTS
BEING FURTHER SOUTH AND SOUTHWEST WITH THE QPF CORE AS THE PRIMARY
THETA_E RIDGE CORRELATES WELL WITH THE HEAVIEST PRECIP AS
CONVECTIVE MAGNITUDES WILL LIKELY BE MAXIMIZED WITHIN THAT DEEPER
MOIST, UNSTABLE ENVIRONMENT. GLOBAL DETERMINISTIC IS ALREADY
BEGINNING TO SHOW SIGNS OF LEANING IN THAT DIRECTION WITH THE 12Z
ECMWF THE MOST NOTABLE IN THE SOUTHERN ALIGNMENT OF THE HEAVIER QPF
FOOTPRINT. THIS ACTUALLY MATCHES THE ECAIFS, TO A DEGREE IN ITS
PRESENTATION, ANOTHER FAVORED OVERLAP THAT TENDS TO VERIFY WELL
ONCE WE REACH INSIDE 72 HRS FROM AN EVENT. IN THIS CASE, THE MAIN
AREA OF INTEREST WILL LIKELY BE A LITTLE FURTHER SOUTH AND
SOUTHWEST COMPARED TO WHAT WAS FORECAST PREVIOUSLY IN REGARDS TO
THE SLGT RISK. THAT SAID, THERE'S STILL HINTS THE OVERALL
MERIDIONAL PATTERN INVOLVED COULD STILL ENHANCE HEAVIER
PRECIPITATION FURTHER NORTH INTO THE MIDWEST WHERE THE PREVIOUS
SLGT RISK WAS ALIGNED. AS A RESULT OF THE TRENDS AND SOME
CONTINUITY, DECIDED TO EXPAND UPON THE SLGT RISK FURTHER SOUTH WITH
THE HIGHEST CONFIDENCE IN HEAVY PRECIP LIKELY LYING WITHIN THE
MISSOURI VALLEY DOWN INTO PERHAPS EASTERN KS AS THE UPPER JET
PRESENTATION WOULD LIKELY PROMOTE THE BEST THE LER DYNAMICS OVER
THAT PARTICULAR CORRIDOR. THIS IS A PERIOD TO MONITOR CLOSELY AS
THE EXPANSE OF HEAVIER PRECIP WILL LIKELY PRODUCE SCATTERED FLASH
FLOOD PROSPECTS GIVEN THE ENVIRONMENTAL FAVORABILITY, AS WELL AS
THE LOWER FFG'S IN PLACE ACROSS NORTHERN MO DOWN INTO EASTERN KS.
ANY FURTHER SOUTH PUSH WOULD PUT OK IN PLAY AS WELL, SO THIS
FORECAST COULD BE A BIT FLUID PENDING THE CONTINUED TRENDS.
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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