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FOUS30 KWBC 271857
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
257 PM EDT MON JUL 27 2026
DAY 1
VALID 1832Z MON JUL 27 2026 - 12Z TUE JUL 28 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN EFFECT FOR PARTS
OF SOUTHEAST WISCONSIN, NORTHEAST/EAST-CENTRAL ILLINOIS, AND
NORTHWEST/WEST-CENTRAL INDIANA...
1830Z SPECIAL UPDATE...
A SLGT RISK WAS ADDED TO PARTS OF THE MIDWEST FROM SE WI THROUGH
MUCH OF NE IL AND NW IN, INCLUDING THE CHICAGO, INDIANAPOLIS, AND
MILWAUKEE METRO REGIONS. THIS IS DUE TO ONGOING HEAVY RAINFALL AND
THE EXPECTATION FOR INTENSE RAINFALL RATES TO CONTINUE FOR SEVERAL
HOURS WHILE THE THREAT SLIDES SOUTHWARD WITH TIME. BOTH 17Z RUNS
OF THE HRRR AND RRFS SUPPORT 2-5" ADDITIONAL RAINFALL AMOUNTS
THROUGH 06Z, WHICH WOULD PRODUCE SCATTERED AREAS OF FLASH FLOODING.
URBAN LOCATIONS COULD SEE SIGNIFICANT STREET FLOODING SHOULD
THUNDERSTORMS TRAIN OVER THE REGION. AS THE COMPLEX PUSHES
SOUTHWARD THIS EVENING AND OVERNIGHT ACROSS CENTRAL AND SOUTHERN
IL/IN, RAINFALL RATES AND THE THREAT OF BACKBUILDING STORMS SHOULD
DIMINISH AS BETTER FORCING SHIFTS EASTWARD INTO THE UPPER OHIO
VALLEY. SEE MPD 0861 FOR MORE INFORMATION.
SNELL
PREVIOUS DISCUSSION...
..FOUR CORNERS STATES ONTO THE CENTRAL PLAINS
THE MONSOON RIDGE GETS SLIGHTLY SUPPRESSED SOUTH TODAY BY
SHORTWAVES CRESTING ITS PERIPHERY OVER THE NORTHERN ROCKIES. THIS
WILL SQUELCH THE HIGHER PW A BIT SOUTH FROM PREVIOUS DAYS, BUT
OTHERWISE THE RIDGE REMAINS IN PLACE WITH WEAK IMPULSES ROTATING
AROUND IT TO ENHANCE ASCENT AND RESULTING CONVECTION. ONCE AGAIN,
THE FOCUS FOR THUNDERSTORM DEVELOPMENT WILL BE ACROSS THE HIGHER
TERRAIN LATE THIS MORNING, BEFORE EXPANDING ACROSS THE FOUR CORNERS
STATES, WITH SOME ORGANIZATION POSSIBLE THROUGH 20-30 KTS OF BULK
SHEAR. WHILE PWS WILL STILL BE +1 TO +2 SIGMA FROM AZ THROUGH WY,
THE MOST IMPRESSIVE CAPE (APPROACHING 750 J/KG) LOOK TO BE CONFINED
TO AZ/NM, WHICH CAN BE A BETTER DISCRIMINATOR FOR EXCESSIVE
RAINFALL POTENTIAL WITHIN THE MONSOON. HOWEVER, ANY CONVECTION HAS
THE POTENTIAL TO PRODUCE INTENSE RAIN RATES LEADING TO HOURLY
RAINFALL OF 1-1.5", WHICH COULD PRODUCE AT LEAST ISOLATED FLASH
FLOOD RESPONSES OVER VULNERABLE TERRAIN FEATURES OR BURN SCARS.
STORMS THAT DEVELOP ACROSS UT/WY/CO MAY FEATURE FASTER FORWARD
PROPAGATION (AFTER BRIEF SLOW DOWNS DURING INITIATION) SO THE MRGL
RISK WAS EXPANDED SLIGHTLY INTO THE CENTRAL PLAINS. HOWEVER, THIS
FASTER MOTION SHOULD AT LEAST SOMEWHAT LIMIT THE RUNOFF POTENTIAL.
FARTHER SOUTH INTO AZ A SHORTWAVE MOVING ALONG THE MEXICO/ARIZONA
BORDER WITHIN THE ELEVATED SHEAR MAY HELP ORGANIZED CLUSTERS OF
STORMS MOVING MORE SLOWLY WESTWARD, AND THIS IS REFLECTED BY
ELEVATED (BUT STILL MODEST) PROBABILITIES FOR 3" OF RAIN TODAY.
CONSIDERED A TARGETED SLGT RISK FOR THE TWC CWA BUT SIMULATED
REFLECTIVITY FROM THE CAMS AND THE UA WRF WERE NOT SUFFICIENT FOR
AN UPGRADE AT THIS TIME.
..GREAT LAKES AND OHIO VALLEY INTO THE NORTHEAST US
A POTENT SHORTWAVE DIVING OUT OF ONTARIO ACROSS THE GREAT LAKES
WILL INTERACT WITH A COMPLEX SURFACE PATTERN OVER THE REGION TO
DRIVE SCATTERED TO WIDESPREAD THUNDERSTORMS THROUGH THE DAY.
ACTIVITY THIS MORNING IS ALREADY PRODUCING HEAVY RAINFALL RATES
MEASURED VIA MRMS OF OVER 1"/HR WITHIN THE PRONOUNCED ASCENT AS IT
IMPINGES UPON AN IMPRESSIVE OVERLAP OF PW/CAPE MEASURED VIA MORNING
12Z SOUNDINGS AT APX/GRB OF NEAR RECORD VALUES (1.7-2.1 PWS AND
4000-5000 J/KG CAPE). AS THE AFTN PROGRESSES, CONVECTION WILL
BECOME INCREASINGLY WIDESPREAD AS THE SHORTWAVE DIVES SOUTH AND
PUSHES A COLD FRONT (AND ACCOMPANYING WAVE OF LOW PRESSURE) THROUGH
THE GREAT LAKES AND SOUTHEAST TOWARDS THE OHIO VALLEY/CENTRAL
APPALACHIANS). WHILE THE THERMODYNAMIC ENVIRONMENT WILL SUPPORT
INTENSE RAIN RATES WITHIN ANY THUNDERSTORMS TODAY, AND 40-50KTS OF
BULK SHEAR WILL HELP ORGANIZE STORMS INTO CLUSTERS AND/OR
SUPERCELLS, MEAN WINDS OF 30-40 KTS SUGGEST CONVECTION WILL REMAIN
PROGRESSIVE, AND CORFIDI VECTORS DO NOT SUPPORT MUCH
BACKBUILDING/TRAINING. SO WHILE LOCAL IMPACTS DUE TO FLASH FLOODING
ARE POSSIBLE, THE OVERALL RISK MATCHES BEST THE MRGL RISK CATEGORY
SO THE INHERITED WAS CHANGED ONLY COSMETICALLY FOR NEW GUIDANCE.
..WESTERN FLORIDA PENINSULA
WEAK SHORTWAVE DIVING ALONG OR JUST WEST OF THE FLORIDA PENINSULA
WILL WORK TOGETHER WITH BROAD DIRECTIONAL JET- LEVEL DIFFLUENCE TO
SPAWN REPEATED ROUNDS OF THUNDERSTORM ACTIVITY TODAY. THIS
CONVECTION WILL OCCUR WITHIN ROBUST PW ANOMALIES REACHING +1.5 TO
+2.0 SIGMA FOR THE SOUTHERN HALF OF FLORIDA, WHICH WHEN COMBINED
WITH SBCAPE EXCEEDING 3000 J/KG WILL SUPPORT TORRENTIAL RAIN RATES.
WHILE SHEAR WILL BE MINIMAL INDICATING PULSE-TYPE CONVECTION, WEAK
FLOW AND RESULTING CELL COLLISIONS OR OUTFLOW MERGERS, AS WELL AS
THE GULF BREEZE, WILL SUPPORT SCATTERED TO WIDESPREAD
THUNDERSTORMS, ALL OF WHICH MAY CONTAIN 2-3"/HR RAINFALL. DUE TO
THE NATURE OF THIS CONVECTION, PLACING THE AXIS OF HEAVIEST AMOUNTS
REMAINS UNCERTAIN, BUT THERE IS A COMMON SIGNAL IN BOTH REFS AND
HREF PROBABILITIES FOR LOCALLY MORE THAN 5" (20-40% CHANCE) NEAR
TAMPA BAY, SO THE INHERITED MRGL RISK WAS CONTINUED FOR THIS AREA,
BUT EXPANDED ALONG THE COAST FOR POTENTIAL BENEATH THE FORCING
CREATED BY THE UPPER DIFFLUENCE, AND ADDED THE FLORIDA KEYS AFTER
COORDINATION WITH WFO KEY.
..COASTAL MID-ATLANTIC
A SURFACE TROUGH WILL SHARPEN EAST OF I-95 THIS AFTN PROVIDING A
FOCUS FOR ASCENT AND CONVECTIVE DEVELOPMENT. THE HIGH-RES CAMS
SUGGEST DEVELOPMENT WILL GENERALLY BE ISOLATED, BUT WITHIN
FAVORABLE THERMODYNAMICS CHARACTERIZED BY PWS ABOVE 1.5 INCHES AND
SBCAPE OF 2000 J/KG OR MORE. THIS WILL SUPPORT INTENSE RAIN RATES
WITHIN ANY STORMS THAT DEVELOP, AND BOTH THE REFS AND HREF
NEIGHBORHOOD PROBABILITIES REACH 50-70% FOR HOURLY RAINFALL OF 1
INCH OR MORE. WHILE THERE IS SOME UNCERTAINTY INTO THE COVERAGE AND
PLACEMENT OF ACTIVITY THIS AFTN, THE INHERITED MRGL RISK WAS
CONTINUED WITH JUST SUBTLE COSMETIC MODIFICATIONS SINCE SOILS ARE
SATURATED FROM HEAVY ANTECEDENT RAINFALL.
WEISS
DAY 2
VALID 12Z TUE JUL 28 2026 - 12Z WED JUL 29 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
NORTHERN MID-ATLANTIC INTO SOUTHERN NEW ENGLAND...
...SOUTHERN APPALACHIANS INTO NEW ENGLAND INCLUDING NORTHERN MID-
ATLANTIC...
THE AMPLIFICATION OF A MID- AND UPPER-LEVEL TROUGH MOVING OUT OF
THE GREAT LAKES/OHIO VALLEY ON MONDAY LEADS TO THE DEVELOPMENT OF
SURFACE LOW PRESSURE OVER THE EASTERN GREAT LAKES BY THE START OF
THE DAY 2 PERIOD. HOWEVER...THE LOW STALLS OVER INTERIOR NY/PA ON
TUESDAY. THERE IS HAS BEEN GROWING CERTAINLY ON THE INTERIOR
POSITION OF THIS LOW WHICH THEN MAINTAINS THE WARM SECTOR OVER THE
NORTHERN MID-ATLANTIC COAST INTO SOUTHERN NEW ENGLAND. PRECIPITABLE
WATER VALUES OF 2 INCHES IS HIGHLIGHTED THROUGH THIS WARM SECTOR
WHICH SHOULD ALSO HAVE SUFFICIENT INSTABILITY FOR HIGHER RAINFALL
RATES ALONG WITH DIVERGENCE ALOFT TO PROMOTE GROWTH AND REPEATING
ACTIVITY. A SLIGHT RISK REMAINS OVER THE NORTHERN MID-ATLANTIC
INTO SOUTHERN NEW ENGLAND WITH ADDITIONAL FOCUS NOW ACROSS PARTS OF
NORTHERN NEW JERSEY INTO SOUTHERN NEW YORK (INLAND OF NEW YORK
CITY) INTO WESTERN CONNECTICUT CONSIDERED TO BE HIGHER-END SLIGHT.
ELSEWHERE, WARM SECTOR MOISTURE AND INSTABILITY IS PRESENT DOWN
THE MID-ATLANTIC THROUGH NORTH CAROLINA WITH POTENTIAL FOR SOUTH
MOVING ACTIVITY TO REPEAT FROM REINFORCING SHORTWAVES ROUNDING THE
NEW LOW OT THE NORTH.
..FOUR CORNERS STATES ACROSS THE CENTRAL PLAINS
FURTHER SUPPRESSION OF THE UPPER HIGH CENTER SOUTH THROUGH NEW
MEXICO OPENS THE OPPORTUNITY FOR ADDITIONAL DOWNSTREAM ACTIVITY
FROM THE FOUR CORNERS STATES ACROSS THE CENTRAL PLAINS. THE
MARGINAL RISK WAS EXPANDED EAST TO THE KC METRO. THE RRFS STILL
HIGHLIGHTED THE HIGH PLAINS OF BOTH NORTHEAST AND SOUTHEAST
COLORADO WITH MORE TYPICAL MONSOONAL ACTIVITY OVER TERRAIN IN THE
FOUR CORNERS STATES.
BANN/JACKSON
DAY 3
VALID 12Z WED JUL 29 2026 - 12Z THU JUL 30 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE NORTHEAST WEDNESDAY...
..NORTHEAST
A DYNAMIC COASTAL SYSTEM TAKES EARLIER IN THE WEEK ALONG/NEAR THE
NEW ENGLAND COAST PER MODEL GUIDANCE. STRONG UPPER LEVEL JET
ENERGY UPSTREAM DIVING TOWARD THE TROUGH BASE WILL AMPLIFY THE
UPPER TROUGH -- TO THE TUNE OF 2+ STANDARD DEVIATIONS BELOW LATE
JULY MEANS AT 500 MB-- WHICH ENHANCES THE DOWNSTREAM QG FORCING AS
IT ENCOUNTERS DEEP MOISTURE AT LOW- TO MID-LEVELS BEING DRAWN IN
FROM THE ATLANTIC GULF STREAM, WITH A SWATH OF ~1.75" PWS. AS
PREVIOUSLY NOTED...GIVEN THE PERSISTENCE OF FAVORABLE COOL SEASON
DYNAMICS WITH WARM SEASON THERMODYNAMICS (HIGH DEEP- LAYER
TPW/THETA-E VALUES), HAVE MAINTAINED THE SLIGHT RISK AREA PRETTY
MUCH UNCHANGED ACROSS PARTS OF THE NORTHEAST, WHICH FITS THE MOST
RECENT GLOBAL GUIDANCE RATHER WELL.
OPERATIONAL GUIDANCE SHOWS 2-4 INCHES OF RAINFALL ACROSS THE
SLIGHT RISK AREA FROM WEDNESDAY INTO LATE WEDNESDAY NIGHT/EARLY
THURSDAY MORNING. FRONTOGENESIS OF THE COMMA HEAD COULD ON ITS OWN
LEAD TO EFFICIENT HEAVY RAINFALL; NOT MUCH MU/ML CAPE WILL BE
NECESSARY TO LEAD TO FLASH FLOODING CONCERNS.
..FOUR CORNERS STATES INTO THE CENTRAL/NORTHERN PLAINS
MONSOONAL FLOW, LIKELY TO BE ENHANCED BY GENEVIEVE MOVING OFFSHORE
BAJA CALIFORNIA, BRINGS ELEVATED MOISTURE OVER THE DESERT
SOUTHWEST THROUGH THE CENTRAL ROCKIES AND INTO THE CENTRAL AND
NORTHERN PLAINS. THE MORE SUPPRESSED RIDGE WILL ALLOW MULTIPLE
MESOSCALE/CONVECTIVELY AIDED SHORTWAVES TO PUSH OVER THE TOP/ACROSS
THE ROCKIES INTO THE PLAINS. THE MARGINAL RISK AREA HERE ONLY
NEEDED SOME COSMETIC CHANGES TO BETTER FIT THE MOST RECENT QPF
GUIDANCE BUT THE DIFFERENCES DID NOT REFLECT A CHANGE IN THE
FORECAST REASONING.
..CENTRAL GULF COAST REGION INTO PARTS OF THE SOUTHEAST
NUMERICAL GUIDANCE CONTINUED TO SHOW HEAVY...TO POTENTIALLY
EXCESSIVE...RAINFALL BEING FORCED/FOCUSED BY A COLD FRONT
ASSOCIATED WITH THE CYCLONE IMPACTING NEW ENGLAND. STILL LITTLE
REASON TO QUESTION WHETHER THE MOISTURE WILL BE AMPLE AT THE SAME
TIME THAT THE EFFECTIVE BULK SHEAR IS SUFFICIENT FOR CONVECTIVE
ORGANIZATION. THE INHERITED MARGINAL RISK AREAS FOR WEDNESDAY INTO
THURSDAY NIGHT SAW ONLY A FEW COSMETIC CHANGES TO BETTER FIT THE
MOST RECENT QPF GUIDANCE.
BANN/ROTH
DAY 4 AND DAY 5
VALID 12Z THU JUL 30 2026 - 12Z SAT AUG 01 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE LOWER MISSOURI AND MID TO UPPER MISSISSIPPI VALLEY...
..LOWER MISSOURI VALLEY INTO THE MID-UPPER MISSISSIPPI VALLEY
ON DAY 4 (THURSDAY-THURSDAY NIGHT), CONVECTIVELY-AIDED SHORTWAVE
ENERGY PROGRESSING EAST FROM THE CENTRAL-NORTHERN PLAINS WILL
AMPLIFY A BIT (DIG A BIT FARTHER SOUTH) UPON REACHING THE LOWER MO-
MID MS VALLEYS) DURING THIS TIME AS THE ~600DM 500MB HIGH BECOMES
CENTERED FARTHER WEST TOWARD THE FOUR CORNERS. THERE'S NEAR TO
ABOVE AVERAGE DISCREPANCY AMONGST THE 00Z GLOBAL GUIDANCE. THE GFS/
GEFS MEAN/AIGFS ARE A BIT FARTHER EAST COMPARED TO THE ECMWF/ECENS
MEAN/EC AIFS, WITH THE CMC CAMP BASICALLY IN THE MIDDLE IN TERMS OF
EASTWARD PROGRESSION. IN ADDITION, THERE REMAINS LATITUDINAL
DIFFERENCES WITH THE HEAVIEST QPF, WITH THE 00Z UKMET THE FARTHEST
NORTH. GIVEN THE MCS/UPSCALE GROWTH POTENTIAL WITH THIS SYSTEM,
CONSIDERING THE INFLUX OF 2-2.25+ PWS PER THE GUIDANCE,
CONCENTRATED AREAS OF HEAVY RAIN ARE EXPECTED, ESPECIALLY ACROSS
THE CORN BELT GIVEN THE DEEP-LAYER MOISTURE PROFILE AND HIGH
SURFACE DEWPOINTS. CERTAINLY AN EVENT THAT WOULD WARRANT A SLIGHT
RISK, WHICH FOR NOW WE'VE CONFINED ACROSS EASTERN SD, FAR EASTERN
NE AND NORTHEAST KS, INTO NORTHWEST MO, WESTERN 2/3 OF IOWA, AND
SOUTHERN MN, WHERE THE GLOBAL ENSEMBLE PROBABILITIES OF >3" IN
12/24 HOURS ARE HIGHEST.
ON DAY 5 (FRIDAY-FRIDAY NIGHT), HAVE ESSENTIALLY SHIFTED THE
SLIGHT RISK AREA FARTHER DOWNSTREAM (EAST-SOUTHEAST) PER THE GLOBAL
GUIDANCE CONSENSUS. GLOBALS ALL SHOW SPOTTY HEAVY 24HR RAINFALL
TOTALS, I.E. 3-5+ INCHES, THOUGH AGAIN WITH SOME SPATIAL SPREAD IN
THE GUIDANCE. ECENS QPF EXCEEDANCE PROBABILITIES HAVE COME UP FROM
THE PREVIOUS RUN, AND ARE CERTAINLY HIGHER COMPARED TO THE DAY 4
PERIOD (MORE EXPANDED AREA OF 3 TO 5 INCH PROBABILITIES).
..FOUR CORNERS STATES INTO THE CENTRAL/NORTHERN PLAINS
MONSOONAL FLOW AND ANOMALOUS DEEP-LAYER MOISTURE WILL MAINTAIN A
MARGINAL (ISOLATED) EXCESSIVE RAINFALL RISK OVER EASTERN AZ AND
MUCH OF MN (EXCEPT SE PORTION) INTO SOUTHEAST UT AND THROUGH MUCH
OF CO. THE EXPANDING MID/UPPER LEVEL RIDGE (600DM HEIGHTS AT 500
MB) WILL LIKELY LIMIT THE COVERAGE COMPARED TO RECENT DAYS,
ESPECIALLY BY FRIDAY.
..CENTRAL GULF COAST REGION INTO PARTS OF THE SOUTHEAST
HEAVY RAINFALL IS EXPECTED ALONG THE NEW ENGLAND CYCLONE'S
TRAILING FRONT NEAR THE FL/GA BORDER. MOISTURE SHOULD BE AMPLE AND
THERE COULD BE ENOUGH EFFECTIVE BULK SHEAR FOR CONVECTIVE
ORGANIZATION. THE INHERITED MARGINAL RISK AREAS FOR THURSDAY INTO
FRIDAY NIGHT SAW ONLY A FEW COSMETIC CHANGES TO BETTER FIT THE
MOST RECENT QPF GUIDANCE.
HURLEY
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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