431
FOUS30 KWBC 011556
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1156 AM EDT SAT AUG 1 2026
DAY 1
VALID 16Z SAT AUG 01 2026 - 12Z SUN AUG 02 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE UPPER
MIDWEST TO THE GULF COAST AND FOR NEW MEXICO INTO THE SOUTHERN
HIGH PLAINS...
..UPPER MIDWEST TO THE GULF COAST
AN ANOMALOUSLY STRONG UPPER LOW (NAEFS 500MB HEIGHTS FALLING BELOW
THE 2.5 PERCENTILE, 850MB HEIGHTS TO BELOW THE CLIMO MINIMUM) WILL
PIVOT SLOWLY EASTWARD TODAY, REACHING CENTRAL INDIANA BY THE END
OF THE FORECAST PERIOD. THIS CLOSED LOW WILL DRIVE PRONOUNCED
HEIGHT FALLS AND MID-LEVEL DIVERGENCE FOR ASCENT ACROSS THE AREA,
WHILE THE ACCOMPANYING OCCLUDED SURFACE LOW AND TRAILING COLD FRONT
PUSH INTO THE OHIO AND TENNESSEE VALLEYS. DOWNSTREAM OF THESE
FEATURES, ROBUST THERMODYNAMICS WILL BE DRAWN NORTHWARD FROM THE
GULF, RESULTING IN A CORRIDOR OF MUCAPE ABOVE 1000 J/KG OVERLAPPED
WITH PWS OF 1.75 TO 2.00 INCHES EXTENDING FROM THE FLORIDA
PANHANDLE ALL THE WAY INTO INDIANA.
WITHIN THIS BROAD PLUME OF IMPRESSIVE THERMODYNAMICS, ALL CONVECTION
WHICH DEVELOPS AHEAD OF THE SYSTEM WILL HAVE THE POTENTIAL TO
PRODUCE EXCESSIVE RAIN RATES. THIS IS SUPPORTED BY BOTH HREF AND
REFS NEIGHBORHOOD PROBABILITIES THAT INDICATE A 30-70% CHANCE OF
AT LEAST 1"/HR RATES WITHIN A BROAD AREA WHERE THUNDERSTORMS ARE
EXPECTED TODAY. WITH MEAN 0-6KM WINDS ALIGNED TO THE FRONT,
ESPECIALLY FROM FLORIDA THROUGH KENTUCKY, AT LEAST SHORT DURATION
TRAINING IS EXPECTED, AND THIS RESULTS IN NOTABLE SPATIAL COVERAGE
OF PROBABILITIES ABOVE 40% (ALMOST CONTINUOUS) FOR AT LEAST 3" OF
RAINFALL TODAY FROM FLORIDA TO ILLINOIS. SOME OF THIS WILL BE
MOVING ACROSS VULNERABLE SOILS DUE TO NATURAL SENSITIVITY OF
TERRAIN FEATURES OR FROM RECENT HEAVY RAINS, BUT WITHIN THIS
BROADER AREA THERE ARE TWO FOCUSED REGIONS WITH A SLIGHTLY HIGHER
THREAT TODAY FOR FLASH FLOODING.
1) ILLINOIS INTO INDIANA: HERE, AN IMPRESSIVE DEFORMATION AXIS WILL
SETUP N/NW OF THE MID-LEVEL LOW AS IT PIVOTS E/SE, AND WILL DRIVE
ASCENT INTO AN IMPRESSIVE (ESPECIALLY FOR AUGUST 1) TROWAL AS THE
ACCOMPANYING THETA-E RIDGE PIVOTS CYCLONICALLY AROUND THE SYSTEM.
THIS WILL RESULT NOT ONLY AS A REGION OF INCREASED INSTABILITY AND
MOISTURE, BUT ALSO A GREATER TRAINING RISK AS PROPAGATION VECTORS
AND MEAN WINDS BECOME INCREASINGLY ANTI-PARALLEL. THIS SUGGESTS A
HIGH THREAT FOR BACKBUILDING AND REPEATING CELLS, THROUGH WHICH THE
1-2"/HR RAIN RATES COULD CAUSE LOCALLY MORE THAN 5" OF RAIN (30-50%
CHANCE). ALTHOUGH THE SBCAPE MAY BE SOMEWHAT MUTED HERE, THE
ELEVATED CAPE SHOULD OFFSET THAT LIMITATION, AND AN ENHANCED SLIGHT
RISK CONTINUES WITH ONLY MODEST COSMETIC ADJUSTMENTS.
2) FLORIDA GULF COAST AND PANHANDLE: IMPRESSIVE THERMODYNAMICS
ACTED UPON BY A NOTABLE SHORTWAVE DIGGING ACROSS ALABAMA WILL SPAWN
MULTIPLE ROUNDS OF THUNDERSTORMS TODAY PRODUCING RAINFALL RATES AS
MUCH AS 3"/HR. STORMS WILL LIKELY DEVELOP OVER THE GULF THROUGH
TODAY AND THEN TRAIN TO THE E/NE MOVING SHORE THE CENTRAL/EASTERN
FLORIDA PANHANDLE BEFORE LIFTING NORTHEAST INTO SOUTHERN GEORGIA.
THE COLD FRONT SLOWLY APPROACHING FROM THE NW WILL ADDITIONALLY
CONTRIBUTE ASCENT AND INCREASE SHEAR, SO ORGANIZATION INTO CLUSTERS
IS LIKELY, AND THIS COULD RESULT IN 5+" OF RAIN, WITH LOCALLY UP TO
8" POSSIBLE (10-20% CHANCE). ALTHOUGH THERE IS SOME UNCERTAINTY IN
PLACEMENT OF THE HEAVIEST RAIN AMONG THE VARIOUS DETERMINISTIC
MODELS, BOTH THE HREF AND REFS HAVE THE GREATEST SIGNAL FROM THE
EMERALD COAST THROUGH THE NATURE COAST, AND THEN JUST INLAND.
ALTHOUGH THERE IS CONSISTENCY IN THIS ENSEMBLE SIGNAL, THE
VARIABILITY IN THE GUIDANCE ACROSS A REGION THAT HAS SOME OF THE
HIGHEST FFG IN THE COUNTRY, SUGGESTS THE CURRENT SLGT RISK REMAINS
THE CORRECT LEVEL FOR THIS EVENT, BUT AFTER COORDINATION WITH WFO
TAE A TARGETED ENHANCED SLIGHT WAS ADDED WHERE HEAVY RAIN IS
ONGOING AND BOTH THE REFS AND HREF FOCUS THE GREATEST 24-HR RAIN
PROBABILITIES.
..SOUTHERN ROCKIES/HIGH PLAINS TO THE TEXAS HILL COUNTRY
MONSOON RIDGE GETS SUPPRESSED TO THE SW EVEN FURTHER TODAY AS THE
ANOMALOUS CLOSED LOW AND LONGWAVE TROUGH DIG ACROSS THE
MISSISSIPPI VALLEY. THIS RE-STRUCTURING OF THE RIDGE WILL SQUELCH A
LOT OF MONSOON ACTIVITY TODAY, BUT WEAK SHORTWAVES ROTATING AROUND
THE RIDGE AND SOUTH/SOUTHEAST INTO NM/AZ WILL PROVIDE SUFFICIENT
ASCENT FOR CONVECTION THIS AFTN/EVE. AT THE SAME TIME, A COLD FRONT
DROPPING THROUGH THE MIDDLE OF THE COUNTRY WILL BANK INTO THE HIGH
PLAINS OF NM, PROVIDING AN ADDITIONAL FOCUS FOR ASCENT THROUGH
ACCOMPANYING UPSLOPE FLOW. TOGETHER, THIS WILL CREATE SCATTERED TO
WIDESPREAD THUNDERSTORMS FOR EASTERN NM.
THIS ACTIVITY WILL LIKELY BEGIN ON HIGHER TERRAIN, TYPICAL, BUT
INCREASED EFFECTIVE BULK SHEAR (30-40 KTS BY THIS AFTN) WILL HELP
ORGANIZED CELLS INTO CLUSTERS WHICH WILL THEN DROP STEADILY
SOUTHWARD ON MEAN 0-6KM WINDS OF 10-15 KTS. DESPITE THE STEADY
PROGRESSION OF CELLS TODAY, HOURLY RAINFALL MAY EXCEED 1" IN PLACES
(SUPPORTED BY HREF, REFS, AND THE UA WRF), WHICH COULD CAUSE
EXCESSIVE RAINFALL LEADING TO FLASH FLOODING, ESPECIALLY ATOP
VULNERABLE TERRAIN, BURN SCARS, OR URBAN AREAS. THE GREATEST
COVERAGE OF ACTIVITY IS EXPECTED IN EASTERN NM TODAY WHERE THE
INHERITED SLGT RISK WAS ONLY COSMETICALLY ADJUSTED.
THE OTHER AREA OF INTEREST IS ASSOCIATED WITH AN INCREASING SIGNAL
FOR HEAVY RAINFALL FOR PORTIONS OF WEST TEXAS INTO THE HILL
COUNTRY. THUNDERSTORMS DEVELOPING ALONG THE SOUTHWARD SAGGING COLD
FRONT WILL TAP INTO ROBUST THERMODYNAMICS CHARACTERIZED BY PWS OF
1.75 TO 2.00 AND MUCAPE OF 2000 J/KG. THIS WILL BE MOST IMPRESSIVE
IN A NARROW CHANNEL IMMEDIATELY AHEAD OF THE COLD FRONT, AND WILL
SUPPORT HEAVY RAINFALL RATES OF 2"/HR OR MORE. THE HIGH-RES CAMS
HAVE BECOME MORE AGGRESSIVE WITH CONVECTIVE COVERAGE TODAY, AND
ALTHOUGH CELLS SHOULD MOVE STEADILY S/SW, ANY SHORT TERM TRAINING
THROUGH MODEST SHEAR ALONG THE FRONT COULD PRODUCE 2-3" OF RAIN
WITH LOCALLY HIGHER AMOUNTS. CONSIDERED AN UPGRADE TO A SLGT RISK,
ESPECIALLY NOTING THE CONTINUED ELEVATED 0-40CM SOIL MOISTURE AND
GENERAL SENSITIVITY OF THIS REGION, BUT AFTER COORDINATION WITH
THE IMPACTED WFOS, AND DUE TO UNCERTAINTY IN STORM COVERAGE, OPTED
TO MAINTAIN THE MRGL RISK AT THIS TIME.
WEISS
DAY 2
VALID 12Z SUN AUG 02 2026 - 12Z MON AUG 03 2026
..THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE FLORIDA BIG
BEND REGION, AND OVER PORTIONS OF THE NORTHEAST...
..GULF COAST INTO THE SOUTHEAST
ONSHORE FLOW WILL CONTINUE TO FOCUS HEAVY RAINFALL OVER NORTHERN
FLORIDA AND PARTS OF THE SOUTHEAST. THE MID-LEVEL LOW OVER INDIANA
IS FORECAST TO MOVE EAST/SOUTH ALLOWING FOR HEIGHT FALLS TO REACH
THE GULF COAST AND MAINTAINING S/SW FLOW DOWNSTREAM. AN IMPRESSIVE
PLUME OF PWS ABOVE 2.25" OVERLAPPED WITH MUCAPE OF AROUND 2000
J/KG WILL BE POOLED AHEAD OF THE APPROACHING SURFACE COLD FRONT,
AND IT IS THIS IMPRESSIVE ENVIRONMENT THAT WILL SHIFT NORTHEAST
THUNDERSTORMS WILL BE WIDESPREAD; TRAINING AND BACKBUILDING CAN BE
EXPECTED WITH HOURLY RATES REACHING 2 OR MORE INCHES/HOUR. SEVERAL
LOCATIONS MAY ACCUMULATE 3+ INCHES/24 HOURS THUS MAINTAINING AN
ELEVATED THREAT FOR FLASH FLOODING.
..UPPER MIDWEST TO NORTHEAST AND MID-ATLANTIC REGION
A SLOW MOVING OCCLUDED FRONT WILL BE ADVANCING EASTWARD INTO THE
OHIO VALLEY. IMPRESSIVE THERMODYNAMIC ADVECTION WITHIN THE WARM
SECTOR WILL SURGE NORTHWARD AS 30-40 KTS OF WIND AT 850MB TRANSPORT
PW VALUES OF 1.75 TO 2.0 INCHES ALL THE WAY TO THE CANADIAN BORDER
OVERLAPPING 500-1000 J/KG OF MUCAPE. THIS WILL SUPPORT WIDESPREAD
THUNDERSTORMS WITH RAINFALL RATES OF 1-2"/HR, WITH ORGANIZATION
INTO CLUSTERS FOSTERED VIA 30-35 KTS OF BULK SHEAR.
WITH TIME, WINDS WILL BECOME MORE PARALLEL TO THE FRONT WHICH WILL
INCREASE THE THREAT FOR TRAINING OF CELLS FROM THE MID-ATLANTIC
STATES NORTHWARD INTO UPSTATE NEW YORK. THE CURRENT SLIGHT RISK IS
FOCUSED FROM EASTERN LOWER MICHIGAN NORTHEAST TOWARDS THE
ADIRONDACKS WHERE AN IMPRESSIVE DEFORMATION AXIS WILL DEVELOP AND
LAY BENEATH A RARE AUGUST-TROWAL TO ENHANCE BOTH ASCENT AND
INSTABILITY. HERE, MEAN WINDS BECOME ANTI-PARALLEL TO THE
PROPAGATION VECTORS, AND IT IS LIKELY THAT SOME SLOW
MOVING/BACKBUILDING CELLS WILL BRING HEAVY RAINFALL TO AREAS
INCLUDING DETROIT, CLEVELAND, AND BUFFALO. THIS IS WHERE THE
GREATEST EXCESSIVE RAINFALL RISK EXISTS AND WHERE THE HIGHEST
PROBABILITIES FOR RAINFALL EXCEEDING 3"/24HRS.
..SOUTHWEST
FAVORABLE INSTABILITY AND MOISTURE WILL BE A BIT SUPPRESSED DURING
THIS PERIOD THANKS TO THE WITH THE SOMEWHAT FLATTENED RIDGE
DOWNSTREAM. THE ANOMALOUS PW VALUES AND SBCAPE ABOVE 1000 J/KG WILL
GENERALLY BE CONFINED TO THE MOGOLLON RIM AND SOUTHERN VICINITY.
CONVECTION IS STILL LIKELY TO BLOSSOM ACROSS ARIZONA AND NEW MEXICO
AND STORMS THAT DEVELOP MAY ORGANIZE SLIGHTLY TO MOVE SOUTHWEST
OFF THE TERRAIN. A MARGINAL RISK AREA REMAINS IN EFFECT FOR THIS
PERIOD.
CAMPBELL/WEISS
DAY 3
VALID 12Z MON AUG 03 2026 - 12Z TUE AUG 04 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE NORTHERN
MID-ATLANTIC INTO SOUTHERN NEW YORK STATE AND SOUTHERN NEW
ENGLAND...
..PORTIONS OF THE EAST COAST AND OHIO VALLEY
AN AXIS OF ANOMALOUS PW VALUES, 2+ STANDARD DEVIATIONS ABOVE THE
MEAN, 2 TO 2.25" PW VALUES, WILL STRETCH FROM NORTH FLORIDA,
NORTHEASTWARD ACROSS THE COASTAL SOUTHEAST, MID- ATLANTIC AND FROM
EASTERN NEW YORK STATE INTO NEW ENGLAND WILL SUPPORT LOCALLY HEAVY
RAINFALL. A SLIGHT RISK REMAINS OVER PORTIONS OF THE NORTHERN MID-
ATLANTIC (INCLUDING PORTIONS OF NY) INTO SOUTHWEST NEW ENGLAND
WHERE RECENT HEAVY RAINS HAVE LOWERED FFG VALUES/SATURATED SOILS.
DURING THE DAY THE CLOSED LOW IS FORECAST TO SLOW/STALL WHILE
MAINTAINING AN AREA OF ANOMALOUS PW VALUES EAST OF THIS CLOSED
LOW, ACROSS THE UPPER OHIO VALLEY INTO THE MID- ATLANTIC, SOUTHERN
NEW ENGLAND AND SOUTH INTO THE COASTAL SOUTHERN MID-ATLANTIC. A
BROAD MARGINAL RISK AREA WAS DEPICTED IN THIS ANOMALOUS PW AXIS FOR
LOCALLY HEAVY RAINS AND ISOLATED RUNOFF ISSUES.
..SOUTHWEST/SOUTHERN HIGH PLAINS
CONVECTION WILL BECOME LESS SUPPRESSED AS THE RIDGE BUILDS TO THE
EAST ALLOWING FOR MORE MONSOONAL MOISTURE AND INSTABILITY TO REACH
THE SOUTHERN ROCKIES/ADJACENT HIGH PLAINS. LOCALLY HEAVY RAINFALL
WITH ISOLATED RUNOFF ISSUES POSSIBLE FOR THIS PERIOD. A MARGINAL
RISK SPANS FROM SOUTHEAST ARIZONA INTO NEW MEXICO AND SOUTH-
CENTRAL COLORADO.
..PORTIONS OF THE CENTRAL/NORTHERN PLAINS AND MIDWEST
AREAL AVERAGE OF 1-2 INCHES EXPECTED AS A SURFACE FRONT ADVANCES
SOUTHEASTWARD FROM THE UPPER MISSISSIPPI VALLEY INTO THE UPPER
LAKES AND SOUTH THROUGH THE CENTRAL PLAINS. MOIST SOUTHERLY LOW
LEVEL INFLOW INTO THE FRONT AT THIS TIME MAY SUPPORT ORGANIZED
CONVECTION, HEAVY RAINS AND ISOLATED RUNOFF ISSUES. A MARGINAL RISK
IS IN AFFECT FOR NORTHERN MINNESOTA, EASTER NORTH DAKOTA AND
NORTHEAST SOUTH DAKOTA.
CAMPBELL/ROTH
DAY 4 AND DAY 5
VALID 12Z TUE AUG 04 2026 - 12Z THU AUG 06 2026
...THERE ARE MARGINAL RISKS OF EXCESSIVE RAINFALL FROM THE UPPER
OHIO VALLEY/EASTERN LAKES INTO THE NORTHEAST, FROM THE CENTRAL
PLAINS IN THE MID TO UPPER MISSISSIPPI VALLEY AND OVER THE
SOUTHWEST...
...UPPER OH VALLEY, CENTRAL APPALACHIANS, LOWER LAKES, MID-ATLANTIC
INTO THE NORTHEAST...
VERY LITTLE MOVEMENT EXPECTED DAY 4 TO THE CLOSED LOW IN THE
VICINITY OF EASTERN KY/EASTERN TN, WITH THEN A NORTHEASTWARD PUSH
INTO THE EASTERN LAKES ON WEDNESDAY AS IT BEGINS TO WEAKEN. A BROAD
REGION OF ANOMALOUS PW VALUES WILL PERSIST DAY 4 AND DAY 5 TO THE
EAST OF THIS CLOSED LOW FROM THE UPPER OH VALLEY, CENTRAL
APPALACHIANS, EASTWARD INTO THE MID- ATLANTIC, MUCH OF NY STATE AND
SOUTHERN NEW ENGLAND. CONFIDENCE IS LOW WITH QPF DETAILS, BUT
THERE WILL LIKELY BE AREAS OF HEAVY RAINS BOTH DAY 4 AND 5 ACROSS
THESE AREAS WITH ISOLATED RUNOFF ISSUES POSSIBLE. GIVEN THE
UNCERTAINTIES WITH DETAILS, THE RISK LEVEL WAS KEPT AT MARGINAL FOR
BOTH DAY 4 AND 5.
..SOUTHWEST/SOUTHERN HIGH PLAINS
FOR BOTH DAY 4 AND 5, 1200 UTC TUESDAY TO 1200 UTC THURSDAY, A
MARGINAL RISK WAS DEPICTED FOR MONSOONAL CONVECTION ACROSS SOUTHERN
ARIZONA INTO NEW MEXICO. NOT A LOT OF CONFIDENCE WITH QPF DETAILS
HERE, BUT LOCALLY HEAVY RAINS AND ISOLATED RUNOFF ISSUES POSSIBLE
IN THE ABOVE AVERAGE PW VALUES EXPECTED ACROSS THIS AREA.
..CENTRAL PLAINS INTO THE MID TO UPPER MS VALLEY
A SURFACE FRONTAL BOUNDARY IS EXPECTED TO REMAIN NEARLY STATIONARY
DURING THE DAY 4 AND DAY 5 TIME PERIOD FROM THE CENTRAL PLAINS,
EAST-NORTHEASTWARD INTO THE MID TO UPPER MS VALLEY REGION. THIS
FRONT WILL BE SITUATED ALONG THE SOUTHERN EDGE OF THE WESTERLIES
WHERE SHORTWAVE ENERGY PUSHING EAST NORTHEASTWARD ALONG THE FRONTAL
ZONE WILL SUPPORT POTENTIAL FOR ORGANIZED CONVECTION BOTH DAY 4 AND
DAY 5. PW VALUES EXPECTED TO BE SLIGHTLY ABOVE AVERAGE...1.5 TO
1.75"+ IN THE VICINITY OF THIS FRONT, SUPPORTING HEAVY PRECIP
TOTALS WHERE CONVECTION DOES ORGANIZE AND ISOLATED RUNOFF ISSUES.
ORAVEC
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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