314
FOUS30 KWBC 010045
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
845 PM EDT FRI JUL 31 2026
DAY 1
VALID 01Z SAT AUG 01 2026 - 12Z SAT AUG 01 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE MIDWEST & UPPER PENINSULA OF MICHIGAN...
..CENTRAL US SYSTEM
AN EXTREMELY ANOMALOUS MID- LEVEL LOW EXISTS FOR LATE JULY ACROSS
IA. AN IMPRESSIVELY DEEP SYSTEM OVERLAPPING LATE JULY THERMODYNAMICS
IS A CLEAR INDICATOR OF EXCESSIVE RAINFALL POTENTIAL. NEAR THE
OCCLUDED CYCLONE IN IA (AND FARTHER DOWNSTREAM WARM SECTOR) PWS
RANGE FROM 1.75 TO 2.00 INCHES, WITH ML CAPE OF 500-3000 J/KG AT
THE WRITING OF THIS DISCUSSION. EFFECTIVE BULK SHEAR OF 25-35 KTS
SHOULD CONTINUE CONVECTIVE ORGANIZATION. THIS ENVIRONMENT SUPPORTS
HOURLY RAIN AMOUNTS TO 2.5", WITH THE 18Z HREF/12Z REFS SUPPORTING
ADDITIONAL LOCAL TOTALS TO 5" THIS EVENING/TONIGHT. THE THREE
HOURLY FLASH FLOOD GUIDANCE VALUES HAVE LOWERED DUE TO EARLIER
RAINFALL. OVERALL, THE RISK LEVELS FROM CONTINUITY APPEAR
REASONABLE BUT AREAS WERE RESHAPED BASED ON RECENT CONVECTIVE
EVOLUTION AND THE 18Z HREF/12Z REFS GUIDANCE.
..UPPER PENINSULA OF MICHIGAN
INCREASED DEFORMATION BETWEEN 700-500MB PIVOTING INTO THE UPPER
PENINSULA THIS AFTN/EVE ALONG WITH LAKE BREEZE CIRCULATIONS HAVE
LED TO CONVECTION ACROSS EASTERN PORTION OF THE UP OF MI. PWS ARE
AS HIGH AS 1.8 INCHES. ALONG WITH ML CAPE OF 500+ J/KG, HOURLY RAIN
AMOUNTS UP TO 2.5" REMAIN POSSIBLE IN THE SHORT TERM. THIS WOULD
EXCEED THE 3-HR FFG, SUGGESTING AT LEAST SCATTERED INSTANCES OF
FLASH FLOODING ARE POSSIBLE. THE SLIGHT RISK REMAINS INTACT TO DEAL
WITH CONVECTIVE DEVELOPMENT HERE OVER THE NEXT SEVERAL HOURS.
..NORTHERN FLORIDA THROUGH THE CENTRAL GULF COAST
ROBUST LATE-JULY THERMODYNAMICS CHARACTERIZED BY PWS OF 2-2.25
INCHES AND MUCAPE ABOVE 2000 J/KG WILL SPREAD ACROSS THE AREA TODAY
AND TONIGHT AHEAD OF A QUASI-STATIONARY FRONT. AFTERNOON AND
EVENING THUNDERSTORMS ARE PRESENTLY ON THE WANE, BUT A SECONDARY
SIGNAL EXISTS EARLY SATURDAY MORNING, ESPECIALLY ACROSS THE
FLORIDA PANHANDLE AND INTO THE BIG BEND AREA. A SLOW MOVING
SHORTWAVE MOVING WITHIN AN AREA OF THICKNESS DIFFLUENCE LEADS TO A
LONGER PERIOD OF ENHANCED SYNOPTIC LIFT AIDED BY MODEST JET- LEVEL
DIFFLUENCE. LOW-LEVEL INFLOW BACKS SUBTLY MORE TO THE WSW FROM W
AS THE FRONT APPROACHES, DRAWING EVEN MORE IMPRESSIVE PWS ALONG THE
COAST AND INSTABILITY FROM THE GULF. DURING THIS TIME, CORFIDI
VECTORS ARE PROGGED TO COLLAPSE TO 5 KTS OR LESS AND BECOME
INCREASINGLY ANTI- PARALLEL TO THE MEAN WIND SUGGESTING SOME
GREATER BACKBUILDING/TRAINING POTENTIAL WITH RAIN RATES POTENTIALLY
REACHING 3"/HR IF EVERYTHING ALIGNS PERFECTLY PRIOR TO 12Z. THE
18Z HREF/12Z REFS INDICATE THE POTENTIAL FOR LOCAL 2-4" BY 12Z,
WITH THE HREF LESS BULLISH. LEFT THE MARGINAL RISK INTACT BUT
SLIGHT RISK IMPACTS CAN'T BE RULED OUT.
..SOUTHERN-CENTRAL HIGH PLAINS
THE MONSOON RIDGE GETS SUPPRESSED TO THE SOUTH AND WEST IN
RESPONSE TO THE POTENT SYSTEM MOVING THROUGH THE PLAINS/MIDWEST,
WITH A SECONDARY PIECE OF VORTICITY ENERGY DROPPING ACROSS THE
SOUTHERN HIGH PLAINS INTO THE TEXAS PANHANDLE. THIS WILL HELP PUSH
A COLD FRONT THROUGH THE SOUTHERN PLAINS AND BANK AGAINST THE
TERRAIN OF NEW MEXICO LATER THIS EVENING. THE OVERLAPPING ASCENT
FROM THE COLD FRONT AND SHORTWAVE WILL ACT UPON FAVORABLE
THERMODYNAMICS AS A RIBBON OF PWS ABOVE 1.5 INCHES AND POOLED
MUCAPE OF 1000-1500 J/KG GET DRAWN WESTWARD AHEAD OF THE FRONT.
RADAR REFLECTIVITY TRENDS SHOW SOME CLUSTERING OF THUNDERSTORMS IN
EASTERN NM WHICH COULD MERGE INTO PRECEDING ACTIVITY ACROSS
NORTHWEST TX IN THE SHORT TERM. ACTIVITY SHOULD BE ON THE WANE
MIDNIGHT OR SO. LEFT THE MARGINAL RISK LEVEL BUT RESCULPTED THE
AREA TO REFLECT RECENT RADAR REFLECTIVITY AND 18Z HREF/12Z REFS
GUIDANCE.
ROTH
DAY 2
VALID 12Z SAT AUG 01 2026 - 12Z SUN AUG 02 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE THE UPPER
MIDWEST TO THE GULF COAST AND THE SOUTHERN HIGH PLAINS...
..UPPER MIDWEST
A POTENT AND UNSEASONABLY DEEP LOW PRESSURE SYSTEM (ENSEMBLE MEAN
FORECAST MSLP VALUES BELOW THE MINIMUM CFSR CLIMATOLOGICAL) WILL
CONTINUE TO PIVOT ACROSS THE UPPER MIDWEST AS ITS PARENT MID/UPPER
LOW DIGS AND DEEPENS OVER THE REGION. AHEAD OF THE SYSTEM, STRONG
LOW-LEVEL SOUTH AND SOUTHWESTERLY FLOW WILL ADVECT DEEP GULF
MOISTURE (PWS 2-2.25 INCHES/150-175% OF NORMAL) NORTHWARD. COMBINED
WITH IMPRESSIVE DYNAMICS, LARGE SCALE ASCENT, AND SUFFICIENT
INSTABILITY, THE THREAT OF CONVECTIVELY DRIVEN HEAVY RAIN IS
EXPECTED TO CONTINUE INTO DAY 2/SATURDAY, ESPECIALLY WITHIN THE
PIVOTING COMMA HEAD DUE NORTH OF THE LOW TRACK ACROSS PARTS OF
ILLINOIS AND INDIANA. THERE, THE 12Z HREF/RRFS GUIDANCE IS
HIGHLIGHTING THE POTENTIAL FOR SIGNIFICANT QPF, WITH NOTABLE
PROBABILITIES OF EXCEEDING 3"/24 HRS (60-80%) AND 5"/24 HRS
(25-50%). AS A RESULT, THE EXISTING SLGT RISK CAN BE CONSIDERED AN
ENHANCED SLGT FROM EAST-CENTRAL ILLINOIS TO NORTHWEST INDIANA.
ELSEWHERE ACROSS THE OHIO AND TENNESSEE VALLEYS, ONLY COSMETIC
ADJUSTMENTS WERE MADE TO THE SLGT AND MRGL RISKS.
..PARTS OF THE SOUTHEAST TO THE GULF COAST
A MID/UPPER IMPULSE EMBEDDED WITHIN NORTHWESTERLY FLOW ON THE
SOUTHERN PERIPHERY OF THE DEEPENING LOW OVER THE UPPER MIDWEST WILL
DIVE INTO THE SOUTHEAST BEFORE SLOWING DOWN NEAR THE FLORIDA
PANHANDLE DURING THE DAY ON SATURDAY. ANOMALOUSLY HIGH PWS OF
2.25-2.75 INCHES (125-150% OF NORMAL) ALONG WITH 1000-2000+ J/KG OF
MUCAPE WILL SUPPORT NUMEROUS CLUSTERS OF SLOW-MOVING SHOWERS AND
THUNDERSTORMS CONTAINING INTENSE RAINFALL RATES. THE 12Z HREF/RRFS
SHOW FAIRLY WIDESPREAD PROBABILITIES OF 40-90% FOR QPF GREATER THAN
3"/24 HOURS AND 20-60% FOR GREATER THAN 5"/24 HOURS ACROSS PARTS
OF THE SOUTHEAST, ESPECIALLY FOR PORTIONS OF GEORGIA AND THE
FLORIDA PANHANDLE. GIVEN THIS INCREASED SIGNAL FOR POTENTIALLY
SIGNIFICANT RAINFALL, THE SLGT RISK WAS EXPANDED SOUTHWARD TO
INCLUDE SOUTHWEST ALABAMA, SOUTHERN GEORGIA, AND MOST OF THE
FLORIDA PANHANDLE.
..SOUTHERN ROCKIES/HIGH PLAINS TO THE TEXAS HILL COUNTRY
MONSOONAL MOISTURE AND INSTABILITY INTERACTING WITH UPSLOPE FLOW
AND A SOUTHWARD PROGRESSING COLD FRONT WILL SUPPORT SCATTERED
SHOWERS AND THUNDERSTORMS FROM THE SOUTHERN ROCKIES AND HIGH PLAINS
TO THE TEXAS HILL COUNTRY ON DAY 2/SATURDAY. THIS ACTIVITY WILL
HAVE THE POTENTIAL TO PRODUCE HEAVY RAINFALL RATES IN EXCESS OF 1"
PER HOUR, LEADING TO ISOLATED AND SCATTERED INSTANCES OF FLASH
FLOODING. 12Z HREF/RRFS PROBABILITIES FOR QPF GREATER THAN 3"/24
HOURS ARE 20-50% AND MOSTLY CONCENTRATED ACROSS THE SOUTHERN HIGH
PLAINS OF NEW MEXICO. THE EXISTING SLGT RISK COVERING THAT AREA
LOOKED ON TRACK SO MINIMAL CHANGES WERE MADE. HOWEVER, THE
HREF/RRFS IS ALSO BEGINNING TO HIGHLIGHT THE TEXAS HILL COUNTRY
WITH A 10-40% CHANCE FOR QPF GREATER THAN 3"/24 HOURS. ALSO NOTABLE
ARE THE VERY LOW BUT NON-ZERO PROBABILITIES FOR GREATER THAN 5"/24
HRS (5-10%). AS A RESULT, THE MRGL RISK WAS EXPANDED EASTWARD FROM
FAR WESTERN TEXAS WITH THIS UPDATE, AND A FUTURE UPGRADE TO A SLGT
RISK CAN'T BE RULED OUT.
MILLER
DAY 3
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
LONG DURATION ONSHORE FLOW EVENT FROM THE GULF CONTINUES INTO D3
BRINGING HEAVY RAIN TO THE BIG BEND AREA OF FLORIDA AND PORTIONS OF
THE SOUTHEAST.
A POTENT CLOSED MID-LEVEL LOW CENTERED OVER INDIANA SUNDAY MORNING
WILL ROTATE E/SE THROUGH D3 BRINGING HEIGHT FALLS TO THE GULF
COAST, AND KEEPING PRONOUNCED S/SW FLOW DOWNSTREAM. AS THIS CLOSED
LOW ELONGATED TO BECOME AT LEAST SUBTLY MORE N-S ORIENTED, ONSHORE
FLOW FROM THE GULF WILL LOCALLY BACK AND INTENSIFY, DRAWING ROBUST
THERMODYNAMICS NORTHWARD INTO FLORIDA/GEORGIA. 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 THROUGH D3.
WITHIN THIS SETUP, WIDESPREAD THUNDERSTORMS ARE LIKELY, AND WITH
MEAN 0-6KM WINDS ALIGNED PARALLEL TO THE FRONT ONSHORE, AND ANTI-
PARALLEL TO THE CORFIDI VECTORS, THE SETUP APPEARS TO SUGGEST A
HIGH THREAT FOR BACKBUILDING AND TRAINING CONVECTION WITH HEAVY
RAINFALL RATES OF 2"/HR OR MORE. THIS WILL RESULT IN LOCALLY MORE
THAN 3" OF RAINFALL (SREF/GEFS/ECENS PROBABILITIES FOR 3"/24 HRS AS
HIGH AS 10%) FALLING ATOP SATURATED SOILS FROM ANTICIPATED HEAVY
RAIN ON D2. FOR THIS REASON A SLGT WAS ADDED NEAR THE FLORIDA BIG
BEND REGION, WITH THE MRGL EXPANDED NORTHEAST FROM INHERITED.
..UPPER MIDWEST TO NORTHEAST AND MID-ATLANTIC REGION
THE ANOMALOUS MID-LEVEL LOW WILL CONTINUE TO TRACK SLOWLY EASTWARD
FROM THE MIDWEST INTO THE OHIO VALLEY ON SUNDAY AND SUNDAY NIGHT.
BENEATH THIS UPPER LOW, AN OCCLUDED SURFACE CYCLONE WILL TRACK
EASTWARD IN TANDEM, WITH THE ACCOMPANYING FRONTS PRODUCING LOCALLY
ENHANCED ASCENT WITHIN THEIR VICINITY DUE TO OVERRUNNING AND/OR
CONVERGENCE. AS THE WAVE PUSHES EAST, IMPRESSIVE THERMODYNAMIC
ADVECTION WITHIN THE WARM SECTOR WILL SURGE NORTHWARD AS 30-40 KTS
OF WIND AT 850MB TRANSPORT PWS 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.
WITHIN THIS WARM SECTOR, PROPAGATION VECTORS AND MEAN 0-6KM WINDS
WILL BECOME INCREASINGLY PARALLEL AND ALIGNED TO THE APPROACHING
FRONT, WHICH SUGGESTS AN INCREASING TRAINING THREAT FROM THE MID-
ATLANTIC STATES NORTHWARD INTO UPSTATE NY. THE GUIDANCE HAS TRENDED
UPWARD IN QPF FOR THIS AREA, AND AN UPGRADE TO A SLGT RISK IN PARTS
OF THIS AREA MAY BE NEEDED WITH LATER ISSUANCES. HOWEVER, THE
CURRENT SLGT 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 ON D3. THIS IS WHERE THE
GREATEST EXCESSIVE RAINFALL RISK EXISTS, AND THE INHERITED SLGT
RISK WAS MODIFIED TO ACCOUNT FOR RECENT GUIDANCE AND HIGHEST
(ALBEIT STILL MODEST) PROBABILITIES FOR RAINFALL EXCEEDING
3"/24HRS.
..SOUTHWEST
THE MID-LEVEL RIDGE RESPONSIBLE FOR THE MONSOON WILL REMAIN
SOMEWHAT FLATTENED SUNDAY INTO MONDAY /D3/ BUT BEGIN TO EXPAND
EASTWARD ONCE AGAIN AS THE DOWNSTREAM TROUGH ADVECTS EAST INTO THE
MID-ATLANTIC STATES. THIS WILL KEEP MUCH OF THE FAVORABLE
INSTABILITY AND MOISTURE SUPPRESSED TO THE SOUTHERN EDGE OF THE
TYPICAL MONSOON REGION, WITH BOTH ANOMALOUS PWS AND SBCAPE ABOVE
1000 J/KG CONFINED TO GENERALLY THE MOGOLLON RIM AND POINTS SOUTH.
CONVECTION IS STILL LIKELY TO BLOSSOM ACROSS AZ/NM, AND STORMS THAT
DEVELOP MAY ORGANIZE SLIGHTLY WITHIN 25 KTS OF BULK SHEAR TO MOVE
SW OFF THE TERRAIN AT 10-15 KTS. HOWEVER, THE COVERAGE AND SPEED OF
CONVECTION SHOULD LIMIT EXCESSIVE RAINFALL POTENTIAL TO BE
ISOLATED, SO THE MRGL RISK WAS MAINTAINED WITH ONLY SUBTLE COSMETIC
ADJUSTMENTS.
WEISS
DAY 4 AND DAY 5
VALID 12Z MON AUG 03 2026 - 12Z WED AUG 05 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/GREAT LAKES/OH VALLEY
THE WELL-DEFINED UPPER LEVEL TROUGH MOVING THROUGH THE OHIO VALLEY
WILL BEGIN TO FRACTURE ON THURSDAY. THERE IS AGREEMENT THAT 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 NY STATE INTO NEW ENGLAND. GENERALLY FAVORABLE RIGHT
ENTRANCE REGION JET DYNAMICS WILL ACCENTUATE LIFT IN THIS ANOMALOUS
PW AXIS, SUPPORTING POTENTIAL FOR LOCALLY HEAVY RAINFALL TOTALS. 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.
THE CLOSED LOW OVER THE UPPER OH VALLEY WILL BECOME NEARLY
STATIONARY ON FRIDAY. AN AREA OF ANOMALOUS PW VALUES WILL REMAIN
TO THE EAST OF THIS CLOSED LOW, ACROSS THE UPPER OH 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. THE SURFACE FRONT MOVING THROUGH NEW ENGLAND THURSDAY MAY
BECOME STATIONARY AND WEST TO EAST ORIENTED ACROSS SOUTHERN NEW
ENGLAND INTO THE NORTHERN MID-ATLANTIC FRIDAY. A FEW MODELS ARE
SHOWING MORE DEFINED HEAVY RAINS IN THE VICINITY OF THIS FRONT
WHERE THERE IS POTENTIAL FOR PERSISTENT SOUTH SOUTHWESTERLY INFLOW.
STILL A LOT OF SPREAD WITH QPF DETAILS, WARRANTING ONLY A MARGINAL
RISK AT THIS TIME, WITH CHANGES POSSIBLE WITH FUTURE UPDATES.
..SOUTHWEST/SOUTHERN HIGH PLAINS
FOR THURSDAY AND FRIDAY, 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.
..PORTIONS OF THE CENTRAL/NORTHERN PLAINS & MIDWEST
A SURFACE FRONT EXPECTED TO PUSH SOUTHEASTWARD FROM THE UPPER MS
VALLEY INTO THE UPPER LAKES AND SOUTH THROUGH THE CENTRAL PLAINS.
ON THURSDAY, THERE IS A DECENT MODEL SIGNAL FOR 1-2" OF RAIN WHICH
COULD FALL IN A SHORT PERIOD OF TIME, SO ADDED A MARGINAL RISK AREA
FOR PORTIONS OF THE DAKOTAS AND NORTHERN MN -- IT WOULD NOT BE A
SURPRISE IF THE GUIDANCE TRENDED UPWARD ON AMOUNTS. FOR FRIDAY, A
MODEL CONSENSUS EXISTS FOR AN AXIS OF POTENTIALLY HEAVY RAINS FROM
NEBRASKA, EASTWARD INTO IOWA AND SOUTHERN MN WHERE THE FRONT MAY
BECOME MORE WEST TO EAST ORIENTED. MOIST SOUTHERLY LOW LEVEL
INFLOW INTO THE FRONT AT THIS TIME MAY SUPPORT ORGANIZED
CONVECTION, HEAVY RAINS AND ISOLATED RUNOFF ISSUES.
ROTH
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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