934
FOUS30 KWBC 300047
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
847 PM EDT TUE JUL 29 2025
DAY 1
VALID 01Z WED JUL 30 2025 - 12Z WED JUL 30 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL AND NORTHERN PLAINS AND FOR PORTIONS OF THE SOUTHWEST...
OVERALL, THE RISK AREAS STRONGLY RESEMBLE CONTINUITY. SOME CARVING
OUT OF THE RISK AREAS HAS BEEN MADE TO ACCOUNT FOR PLACES WHERE THE
THREAT APPEARS TO BE DIMINISHED WHERE CONVECTION HAS MOVED ALONG.
..ROCKIES EASTWARD INTO THE MIDWEST
AN INSTABILITY GRADIENT EXISTS FROM THE SD/NE BORDER INTO CENTRAL
IA WHICH IS SUPPORTING FORWARD PROPAGATING CONVECTION ACROSS SD,
WHICH PER THE 18Z HREF IS A FEW HOURS AHEAD OF SCHEDULE AS OF 00Z.
POST-FRONTAL UPSLOPE FLOW ALONG WITH SUFFICIENT INSTABILITY LED TO
AFTERNOON STORM DEVELOPMENT IN A COUPLE SECTIONS OF THE ROCKIES.
GUIDANCE CONTINUES TO SUGGEST UPSCALE DEVELOPMENT INTO A COUPLE
MCS'S. ML CAPE VALUES OF 6000+ J/KG EXISTS FROM NE INTO IA. PWATS
ARE 1.5-2" IN THE MIDWEST AND 0.75" IN THE HIGH PLAINS, OR 1.5 TO
2 STANDARD DEVIATIONS ABOVE THE LATE JULY MEAN. THIS COMBINATION
SUPPORTS INTENSE THUNDERSTORMS CAPABLE OF HEAVY RAINFALL WITH
HOURLY RAIN AMOUNTS UP TO 2.5-3" PER HOUR IS POSSIBLE.
INSTANTANEOUS RAIN RATES OF 5-7" AN HOUR WOULDN'T BE SURPRISE NEAR
THE AREA OF STRONGEST INSTABILITY. LOCAL TOTALS IN THE 3-6" RANGE
ARE POSSIBLE OVERALL THROUGH WEDNESDAY 12Z. THIS CONTINUES TO
SUPPORT HIGHER- END SLIGHT RISK PROBABILITIES FOR AREAS IN AND NEAR
IA.
..SOUTHWEST
THUNDERSTORMS ARE INBOUND INTO SOUTHERN NM FROM SOUTH OF THE BORDER.
THIS ACTIVITY SUPPORTS THE ADVERTISED FLASH FLOOD RISK FOR THE AREA
THIS EVENING INTO TONIGHT. HOURLY RAIN AMOUNTS OF 1-2" ARE
POSSIBLE. THE BIGGEST CONCERN IS NEAR AREA BURN SCARS.
..SOUTHEAST
ACTIVITY PERSISTS ACROSS THE APPALACHIANS AND SOUTHEAST, WHICH
SHOULD PERSIST FOR A FEW MORE HOURS. OTHER ACTIVITY IS POSSIBLE IN
THE MORNING HOURS NEAR SOUTHERNMOST NC.
ROTH/PUTNAM/CHENARD
DAY 2
VALID 12Z WED JUL 30 2025 - 12Z THU JUL 31 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE MIDDLE MISSISSIPPI VALLEY AND FOR PORTIONS OF THE FRONT RANGE
AND ADJACENT HIGH PLAINS...
..2030Z UPDATE
CONFIDENCE REMAINS LOW IN THE EXACT CONVECTIVE EVOLUTION ACROSS
THE MISSOURI TO THE MIDDLE MISSISSIPPI VALLEY AND ADJACENT GREAT
LAKES REGION ON WEDNESDAY. NOW AVAILABLE HI-RES GUIDANCE FOLLOWS
PRIOR THINKING THAT AN ONGOING MCS FROM THE DAY 1 PERIOD WILL
CONTINUE EASTWARD ACROSS THE SLIGHT RISK AREA, MOST LIKELY FROM
CENTRAL/EASTERN IOWA INTO NORTHERN ILLINOIS. SOURCES OF ADDITIONAL
CONVECTIVE DEVELOPMENT WEDNESDAY AFTERNOON ARE APPARENT SOUTH AND
WEST OF THE INITIAL MCS ACROSS CENTRAL ILLINOIS AND WESTWARD
THROUGH THE MISSOURI VALLEY ALONG ANY OUTFLOW BOUNDARY(S), THE SLOW
MOVING COLD FRONT, AND SUPPORTED BY THE PASSAGE OF AN UPPER- LEVEL
SHORT-WAVE. DEPENDING ON HOW/WHERE AVAILABLE HIGHER INSTABILITY
AND PWATS ARE PRESENT IN VICINITY OF THESE FEATURES AWAY FROM
CONVECTIVE OVERTURNING, THESE FEATURES WOULD SUPPORT A CONTINUED
THREAT OF THUNDERSTORMS PRODUCING HEAVY DOWNPOURS (1-2"+/HR RATES)
AND HEAVIER RAINFALL TOTALS (2-3"+). THIS IS ESPECIALLY TRUE WHERE
ANY STORMS REPEAT OVER ANY PRIOR RAINFALL AND/OR TRAIN PARALLEL TO
ANY OUTFLOW BOUNDARIES OR THE SLOW MOVING COLD FRONT. A CORRIDOR OF
HIGHER PROBABILITIES MAY BE REQUIRED GIVEN THE SIGNAL FOR HEAVY
DOWNPOURS AND THE POTENTIAL FOR TRAINING AND/OR MULTIPLE ROUNDS OF
CONVECTION. HOWEVER, GIVEN THE NOTED UNCERTAINTIES WITH THE
LOCATION OF ONGOING AND RENEWED CONVECTION THAT WOULD DETERMINE A
MORE SIGNIFICANT THREAT, A BROAD SLIGHT RISK REMAINS SUFFICIENT.
FOR THE CENTRAL/SOUTHERN HIGH PLAINS AND ADJACENT PLAINS, THE
PRIOR FORECAST REMAINS ON TRACK BASED ON NOW AVAILABLE HI-RES
GUIDANCE. THE ONE ADJUSTMENT MADE FOR THIS ISSUANCE WAS TO EXTEND
THE SLIGHT RISK FURTHER SOUTH/SOUTHWEST ACROSS EASTERN NEW MEXICO
TO THE SACRAMENTO MOUNTAIN VICINITY GIVEN A NOTABLE SIGNAL FOR
LOCALLY HEAVIER RAINFALL (1-3") AND ONGOING BURN SCAR
SENSITIVITIES.
PUTNAM
..PREVIOUS DISCUSSION
..MID MS VALLEY
AT 12Z WEDNESDAY IT SEEMS LIKELY THAT WE WILL HAVE SOME DEGREE OF
ORGANIZED CONVECTION ONGOING IN THE VICINITY OF IA. IT APPEARS
PROBABLE THAT A BETTER DEFINED SHORTWAVE/MCV WILL BE ASSOCIATED
WITH THIS CONVECTION AND SLOWLY MOVE EAST ACROSS IA/MO/IL AND
VICINITY WEDNESDAY INTO WEDNESDAY NIGHT. MEANWHILE WE WILL HAVE A
SLOWLY SOUTHWARD SHIFTING COLD FRONT HELPING FOCUS CONVERGENCE, AND
THE RIGHT ENTRANCE REGION OF THE UPPER JET ADDING SOME DIVERGENCE
ALOFT. WITH PLENTIFUL CAPE NEAR THE FRONT AND PWS LOCALLY OVER 2",
THE INGREDIENTS FOR AREAS OF EXCESSIVE RAINFALL ARE IN PLACE.
THERE IS ACTUALLY QUITE A BIT OF UNCERTAINTY WITH THE CONVECTIVE
DETAILS WEDNESDAY INTO WEDNESDAY NIGHT. THERE HAS BEEN A SUBTLE
NORTHWARD SHIFT IN THE FORECAST MCV LOCATION, SEEMINGLY NOW
TRACKING ACROSS IA INTO NORTHERN IL. HOWEVER THE NORTHERN EXTENT
OF THE EXCESSIVE RAINFALL RISK WILL LIKELY BE CAPPED BY A LACK OF
INSTABILITY WELL NORTH OF THE COLD FRONT. THE 00Z ECENS AND AIFS
ENSEMBLES ARE FOCUSING THE BEST RAINFALL POTENTIAL FROM EASTERN IA
INTO NORTHERN IL. THIS SEEMS REASONABLE, ALTHOUGH THE MAGNITUDES
REMAIN IN QUESTION AND ARE DEPENDENT ON THE DEGREE OF INSTABILITY
IN PLACE. THE BETTER INSTABILITY MAY ACTUALLY RESIDE OVER PORTIONS
OF CENTRAL MO INTO CENTRAL IL, AND SO IF CONVECTION IS ABLE TO
ORGANIZE THIS FAR SOUTH THEN A GREATER FLASH FLOOD RISK COULD
EVOLVE. ALL THIS TO SAY THAT CONFIDENCE IS LOW, AND THUS A BROAD
SLIGHT RISK REMAINS TO ENCOMPASS THE VARIOUS POSSIBLE SCENARIOS.
HIGHER END IMPACTS ARE POSSIBLE IN THIS SETUP, BUT FAR FROM
GUARANTEED GIVEN THE QUESTIONS THAT REMAIN REGARDING THE MCV
TRACK/INTENSITY AND INSTABILITY IN PLACE.
..SOUTHWEST AND HIGH PLAINS
ISOLATED TO SCATTERED CONVECTION WILL LIKELY DEVELOP NEAR AREAS OF
TERRAIN FROM NM INTO THE ROCKIES. DAY SHIFT INTRODUCED A SLIGHT
RISK FOR THIS ACTIVITY, AND THAT STILL SEEMS REASONABLE. EASTERLY
LOW LEVEL FLOW INTO THE FRONT RANGE OF CO WILL LIKELY RESULT IN
SLOW CELL MOTIONS AND THE POSSIBILITY OF AT LEAST ISOLATED FLASH
FLOODING. GUIDANCE IS COMING INTO BETTER AGREEMENT THAT SOME
UPSCALE GROWTH AND EASTWARD PROPAGATION INTO NORTHEAST NM,
SOUTHEAST CO AND THE OK PANHANDLE IS PROBABLE AS WELL, FOCUSING
NEAR THE COLD FRONT.
..ELSEWHERE
A BROAD MARGINAL RISK EXTENDS FROM THE CENTRAL GULF COAST ALL THE
WAY INTO PORTIONS OF NEW ENGLAND. HIGH PWS AND CAPE AND CONVECTIVE
COVERAGE WILL DRIVE THE RISK FROM THE GULF COAST INTO THE TN
VALLEY. A LACK OF ORGANIZATION MAY KEEP FFG EXCEEDANCE COVERAGE
DOWN, BUT HIGH RAINFALL RATES WILL LIKELY LOCALLY APPROACH OR
EXCEED FFG. A COLD FRONT WILL DRIVE THE RISK FORM PORTIONS OF THE
OH VALLEY INTO NEW ENGLAND. GENERALLY QUICK CELL MOTIONS AND THE
LACK OF A SIGNIFICANT QPF FOOTPRINT IN THE 00Z MODELS KEEP THIS
RISK AT A MARGINAL LEVEL.
CHENARD
DAY 3
VALID 12Z THU JUL 31 2025 - 12Z FRI AUG 01 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE MID-ATLANTIC INTO SOUTHERN NEW ENGLAND...
..2030Z UPDATE
UPDATED DETERMINISTIC AND ENSEMBLE GUIDANCE HAS COME INTO SOMEWHAT
BETTER AGREEMENT ON THE NOTED FOCUSED CORRIDOR OF QPF ALIGNING
WITH THE SLOW MOVING COLD FRONT STRETCHING FROM THE MID-ATLANTIC
NORTHEASTWARD INTO SOUTHERN NEW ENGLAND, PARTICULARLY WITH THE
NORTHWARD EXTENT OF THE THREAT. THE 12Z GFS/GEFS MEAN AS WELL AS
THE LATEST ECMWF AIFS GUIDANCE STILL SUPPORT A BIT MORE SOUTHERLY
CORRIDOR, ROUGHLY FROM DC TO CHESAPEAKE BAY AND VICINITY
NORTHEASTWARD ALONG I-95 THROUGH PHL AND TO NYC, THOUGH HIGHER QPF
VALUES EXTEND FROM THE NYC VICINITY INTO SOUTHERN NEW ENGLAND. THE
00Z ECENS MEAN AND ESPECIALLY 12Z ECMWF FAVOR A CORRIDOR SHIFTED A
BIT MORE NORTH/WEST OF I-95, WITH PARTICULAR UNCERTAINTY WITH
SOUTHERN EXTENT INTO THE GREATER DC AREA, THOUGH STILL SUPPORT
HIGHER QPF EXTENDING INTO SOUTHERN NEW ENGLAND. OPTED TO BROADEN
THE SLIGHT RISK A BIT FURTHER NORTHWARD ACROSS NEW YORK/NEW ENGLAND
WITH A PARTICULAR CONCERN FOR HIGHER- END SLIGHT RISK IMPACTS
EXTENDING FURTHER NORTH THROUGH THE NYC REGION AND INTO SOUTHERN
NEW ENGLAND GIVEN BETTER AGREEMENT WITH NORTHWARD EXTENT ALONG THE
I-95 CORRIDOR BETWEEN THE GFS/GEFS AND ECWMF- AIFS. THE SOUTHERN
EXTENT OF THE SLIGHT RISK, AS WELL AS CONCERN FOR HIGHER- END
SLIGHT IMPACTS INTO THE GREATER DC AREA, REMAINS DESPITE THE LACK
OF SUPPORT FORM THE ECMWF/ECENS MEANS GIVEN THE NOTED UNCERTAINTY
DISCUSSED WITH RESPECT TO SYNOPTIC SCALE DETAILS OF THE SYSTEM
EVOLUTION.
PUTNAM
..PREVIOUS DISCUSSION
..MID-ATLANTIC INTO NEW ENGLAND
HEAVY RAINFALL AND AT LEAST SOME FLASH FLOODING APPEARS LIKELY
THURSDAY ACROSS PORTIONS OF THE MID-ATLANTIC AND POSSIBLY INTO
SOUTHERN NEW ENGLAND. CONVECTION IS LIKELY TO FOCUS ALONG A SLOW
MOVING COLD FRONT, WITH BROAD MID LEVEL TROUGHING AND HEIGHT FALLS
PROVIDING LARGE SCALE ASCENT. THE UPPER LEVEL JET IS DISPLACED
PRETTY FAR NORTH, HOWEVER STILL LIKELY TO GET SOME ENHANCED UPPER
LEVEL DIVERGENCE INTO THE MID-ATLANTIC FROM THIS FEATURE.
THERE IS QUITE A BIT OF MODEL SPREAD WITH THE DETAILS OF THIS
CONVECTIVE RISK. THE DRIVER OF MOST OF THIS SPREAD APPEARS TO BE A
SHORTWAVE/MCV THAT INTENSIFIES ASSOCIATED WITH THE NE/IA
CONVECTION TUESDAY NIGHT INTO WEDNESDAY. THIS FEATURE THEN TRACKS
EASTWARD AND ENHANCES LIFT OVER THE MID-ATLANTIC AND NORTHEAST.
SOME MODELS HAVE A STRONGER MORE WELL DEFINED FEATURE, WHICH THEN
HELPS KEEP THE FRONT A BIT FARTHER NORTH RESULTING IN A FARTHER
NORTH QPF AXIS. AT THE MOMENT IT DOES SEEM LIKE THE 00Z NAM AND 12Z
ECMWF ARE A BIT TOO AMPLIFIED WITH THIS FEATURE...THUS FIND IT
UNLIKELY THAT THE HEAVIEST QPF SWATH WILL BE AS FAR NORTH AS THEY
DEPICT. THE 00Z ECMWF CAME SOUTH A BIT, BUT PROBABLY STILL TOO FAR
NORTH. BOTH THE 00Z ECMWF AIFS AND 18Z NOAA EAGLE MACHINE LEARNING
ENSEMBLES SHOW HIGHEST PROBABILITIES CLOSER TO THE I95 CORRIDOR,
GENERALLY FROM DC TO PHL TO NYC AND INTO SOUTHERN NEW ENGLAND. THIS
ALSO SEEMS TO FIT THE EXPECTED PLACEMENT OF HIGHER INSTABILITY/PW
OVERLAP. ALSO WILL NOTE THAT THE 00Z RRFS HAS A VERY SIMILAR AXIS
AS WELL. THUS THE SLIGHT RISK WILL REMAIN POSITIONED ACROSS THIS
CORRIDOR, ALTHOUGH CONFIDENCE ON THIS EXACT PLACEMENT REMAINS
AVERAGE AT BEST GIVEN SOME OF THE RUN TO RUN DIFFERENCES WE ARE
SEEING.
WHEREVER THE EVENT DOES FOCUS THERE IS CERTAINLY A POTENTIAL FOR
HIGHER END IMPACTS. PWS NEAR THE SLOW MOVING FRONT WILL BE OVER 2"
OVER A BROAD AREA, WITH EMBEDDED VALUES LIKELY GETTING TOWARDS
2.3". WE SHOULD ALSO HAVE PLENTY OF INSTABILITY TO WORK WITH, WHICH
COMBINED WITH THE HIGH PWS, SHOULD DRIVE HEAVY RAINFALL RATES.
COMBINE THAT WITH SOME TRAINING POTENTIAL NEAR THE SLOW MOVING
FRONT, AND CAN NOT RULE OUT THE POSSIBILITY OF EVENTUALLY NEEDING A
MODERATE RISK...ESPECIALLY IF THE MORE SENSITIVE URBAN CORRIDOR
REMAINS A FOCUS GOING FORWARD.
..GULF COAST INTO OH VALLEY
ANOTHER DAY OF SLOW MOVING PULSE THUNDERSTORMS IS EXPECTED OVER A
LARGE SWATH OF THE REGION. SIMILAR TO WEDNESDAY, HIGH PWS AND CAPE
AND CONVECTIVE COVERAGE WILL DRIVE A LOCALIZED FLASH FLOOD RISK. A
LACK OF ORGANIZATION MAY KEEP FFG EXCEEDANCE COVERAGE DOWN, BUT
HIGH RAINFALL RATES WILL LIKELY LOCALLY APPROACH OR EXCEED FFG.
..ROCKIES INTO THE PLAINS
SCATTERED CONVECTION IS LIKELY FROM EASTERN AZ INTO NM NORTHWARD
ALL THE WAY INTO MT. CURRENTLY NOT SEEING A STRONG INDICATION OF
ORGANIZATION THAT WOULD LEAD TO SLIGHT RISK LEVEL FLASH FLOOD
COVERAGE. HOWEVER LOCALIZED FLASH FLOODING WILL AGAIN BE POSSIBLE
OVER THIS BROAD REGION. THERE ARE SOME HEIGHT FALLS BEGINNING TO
APPROACH FROM THE WEST, SO THAT COULD PERHAPS END UP DRIVING A
MORE ORGANIZED RISK SOMEWHERE WITHIN THIS BROAD MARGINAL RISK. BUT
AT THE MOMENT NOT ENOUGH CONFIDENCE TO GO WITH ANY SLIGHT RISK
AREAS FOR THIS REGION.
CHENARD
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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