256
FOUS30 KWBC 061955
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
355 PM EDT MON JUL 6 2026
DAY 1
VALID 16Z MON JUL 06 2026 - 12Z TUE JUL 07 2026
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF COASTAL NEW JERSEY TO SOUTHEAST MASSACHUSETTS...
16Z UPDATE: TRICKY DAY 1 ERO UPDATE THIS MORNING. DON'T REALLY
THINK ANY OF THE 12Z HIGH RES OR EVEN RECENT HRRR RUNS HAVE A GOOD
HANDLE ON THE CONVECTIVE SITUATION OVER THE MID-ATLANTIC INTO
SOUTHERN NEW ENGLAND. UNUSUAL TO HAVE A MDT RISK IN AN AREA WITH
SUCH LOW CURRENT AND FORECAST INSTABILITY. HOWEVER, WE SHOULD SEE
A RATHER WELL DEFINED SURFACE LOW DEVELOP TODAY SOMEWHERE NEAR OR
SOUTH OF LONG ISLAND. IF THIS LOW BECOMES DEFINED ENOUGH WE COULD
SEE STRONG ENOUGH LOW LEVEL CONVERGENCE AND LIFT TO GENERATE
EFFICIENT WARM RAIN INTO SOUTHERN NEW ENGLAND EVEN WITHOUT MUCH OF
ANY INSTABILITY (WHICH SEEMS TO BE WHAT THE 12Z HRRR IS SHOWING).
CONFIDENCE IN THIS IS LOW...AND COULD VERY WELL SEE THE BETTER
CONVECTION AND HIGHER RATES STAY FROM LONG ISLAND AND POINTS
OFFSHORE. BUT SINCE THE HRRR LIKE SCENARIO OF LOW TOPPED
CONVECTION/WARM RAIN TONIGHT IS A POSSIBILITY, WE WILL MAINTAIN THE
MDT RISK AREA.
OVERALL, HIGHER CONFIDENCE OF FLASH FLOOD IMPACTS FROM COASTAL NJ
INTO PORTIONS OF LONG ISLAND WHERE ENOUGH INSTABILITY SHOULD BE
PRESENT TO DRIVE HIGHER RAINFALL RATES. LOCALLY SIGNIFICANT IMPACTS
ARE A POSSIBILITY. LOWER CONFIDENCE OVER CT/RI/MA, AND CERTAINLY
SOME CHANCE THE HIGHER RAINFALL RATES AND FLASH FLOOD RISK STAY
SOUTH OF THESE AREAS. HOWEVER, THERE IS STILL A CHANCE THAT STRONG
LOW LEVEL LIFT FOCUSED WITHIN THE WARM CLOUD LAYER COULD DRIVE
HIGHER RATES AND A FLASH FLOOD RISK TONIGHT EVEN WITHOUT DEEP
INSTABILITY. THUS WE WILL MAINTAIN CONTINUITY WITH THE MDT RISK
HERE AND CONTINUE TO REASSESS THROUGH THE DAY.
ELSEWHERE, WE EXPANDED THE SLIGHT RISK INTO PORTIONS OF NORTHERN OH
AND SOUTHWEST NY WHERE SLOW MOVING CONVECTION NEAR AN MCV AND
ALONG A FRONT WILL DRIVE AN ISOLATED TO SCATTERED FLASH FLOOD RISK
THROUGH THIS AFTERNOON. ALSO ADDED A MARGINAL RISK ACROSS PORTIONS
OF THE EASTERN DAKOTAS INTO MN WHERE ORGANIZED CONVECTION IS
EXPECTED BY THIS EVENING. WHILE THIS ACTIVITY SHOULD BE
PROGRESSIVE, HIGH RAINFALL RATES AND A FEW CELL MERGERS COULD DRIVE
A LOCALIZED FLASH FLOOD RISK. EXPANDED THE MARGINAL RISK TO
INCLUDE MORE OF TX, WITH A WELL DEFINED MCV DROPPING SOUTH EXPECTED
TO TRIGGER AT LEAST SOME SLOW MOVING CONVECTION LATER TODAY.
CHENARD
..PREVIOUS DISCUSSION
..MID-ATLANTIC AND NORTHEAST
WAVES OF LOW PRESSURE RIPPLE ALONG A LATITUDINALLY WAVERING
STATIONARY FRONT CAUSING MULTIPLE ROUNDS OF TRAINING THUNDERSTORMS.
DURING THIS PERIOD THE FRONT WILL LIKELY BE SPRAWLED FROM CENTRAL
OHIO TO CENTRAL NEW JERSEY. TWO DISTINCT SHORTWAVES MOVING ALONG
THIS FRONT WILL HELP TRACK DUAL WAVES OF LOW PRESSURE EASTWARD,
EACH OF WHICH WILL LOCALLY ENHANCE ASCENT (ONE ACROSS WESTERN
PENNSYLVANIA, THE SECOND FROM NEW JERSEY INTO SOUTHERN NEW
ENGLAND). BROAD AREAS OF ASCENT, INSTABILITY WITH PW VALUES
EXCEEDING 2" WILL BE ALIGNED NEAR THIS FRONT TO YIELD A SIGNIFICANT RISK
FOR HEAVY RAINFALL CAPABLE OF PRODUCING FLASH FLOODING. THE LATEST
GUIDANCE MAINLY FOCUSES THE HEAVIEST QPF OVER SOUTHERN NEW ENGLAND
AND PORTIONS OF NORTHERN/COASTAL NEW JERSEY.
ALTHOUGH THE PLACEMENT WIDELY VARIES AMONG THE HIRES GUIDANCE THERE
CONTINUES TO BE CONSENSUS FOR AREAL AVERAGES OF 3 TO 6 INCHES WITH
LOCAL MAXIMUMS OF 8+ AS REFLECTED BY THE REFS AND HREF PMM. THE
NEIGHBORHOOD PROBABILITIES REACH ABOVE 40% FOR COASTAL NEW
ENGLAND AND LONG ISLAND FOR 3"/24 HR AND 15% FOR 5"/24 HR. RAINFALL
RATES AT TIMES REACHING 2-3"/HR COMBINED WITH ALIGNED MEAN
WIND/CORFIDI VECTORS WHICH ARE PARALLEL TO THE BOUNDARY WILL DRIVE
TRAINING/BACKBUILDING TO SUPPORT THESE HEAVY RAINFALL AMOUNTS. A
MODERATE RISK COVER FAR NORTHEAST NEW JERSEY, SOUTHEAST NEW YORK
AND LONG ISLAND, SOUTHERN CONNECTICUT, SOUTHERN RHODE ISLAND AND
PORTIONS OF SOUTHEAST MASSACHUSETTS.
A BIT FARTHER WEST, A SECONDARY AREA OF LOW PRESSURE INTERACTING
WITH THE SAME THERMODYNAMIC ENVIRONMENT WILL PRODUCE STREAKS OF
HEAVY RAIN PRODUCING CONVECTION FROM WESTERN PENNSYLVANIA THROUGH
THE VICINITY OF WASHINGTON, D.C. WHILE UNCERTAINTY IS A LITTLE
HIGHER IN THIS AREA AS TO THE COVERAGE, SPEED, AND INTENSITY OF THE
THUNDERSTORMS, BOTH THE HREF AND REFS DEPICT A 20-40% CHANCE OF
2"/HR RAIN RATES WITH AT LEAST SHORT-TERM TRAINING POTENTIAL. FFG
ACROSS WESTERN PA IS QUITE LOW (1-1.5"/3HRS) AND HREF/REFS
EXCEEDANCE POTENTIAL IS ELEVATED AS A RESULT. FARTHER SOUTH INTO
THE D.C. AREA, FFG IS HIGHER, BUT THESE INTENSE RATES ATOP MORE
URBAN REGIONS COULD STILL POSE A FLASH FLOOD CONCERN SO A SLIGHT RISK
WAS MAINTAINED.
..ARKLATEX EAST THROUGH THE CAROLINAS
A SLOW MOVING COLD FRONT WILL DROP SLOWLY SOUTHWARD, REACHING A
LINE FROM SOUTHERN ARKANSAS THROUGH EASTERN TENNESSEE BY TUESDAY
MORNING BEFORE STALLING. THIS FRONT WILL SIT WITHIN A PLUME OF
OVERLAPPING ELEVATED PWS (1.75 TO 2.00 INCHES) AND MUCAPE
(1000-2000 J/KG) TO SUPPORT HOURLY RAINFALL OF 1-2" WITH HIGHER
SHORT-TERM RATES. 0-6KM BULK SHEAR IS PROGGED TO BE MINIMAL (LESS
THAN 20 KTS) SO STORMS THAT FORM WILL LIKELY BE OF THE PULSE
VARIETY. REPEATING ROUNDS AND POSSIBLE TRAINING OF HEAVY RAINFALL
WILL KEEP AN ELEVATED THREAT FOR FLASH FLOODING. A MARGINAL RISK
WAS MAINTAINED.
..FLORIDA
DIURNAL HEATING AND ONSHORE FLOW WILL HELP TRIGGER CONVECTION
ALONG THE EASTERN COASTLINE OF FLORIDA WITH 1 TO 3 INCHES AND
ISOLATED LOCAL MAXIMUMS UP TO 5-6 INCHES. A MARGINAL RISK AREA WAS
RAISED FOR THIS PERIOD.
WEISS/CAMPBELL
DAY 2
VALID 12Z TUE JUL 07 2026 - 12Z WED JUL 08 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE NORTHERN PLAINS AND MID-ATLANTIC...
20Z UPDATE: A SLIGHT RISK WAS ADDED ACROSS PORTIONS OF THE MID-
ATLANTIC WHERE CELL MERGERS NEAR A BACKDOOR FRONT SHOULD LEAD TO
ISOLATED TO SCATTERED FLASH FLOODING. PRETTY GOOD AGREEMENT BETWEEN
THE 12Z HREF AND REFS ON THIS AXIS FROM PORTIONS OF SOUTHWEST PA
INTO CENTRAL VA AND NORTHEAST NC, WITH RAINFALL EXPECTED TO
LOCALLY EXCEED 3".
THE MARGINAL RISK WAS EXPANDED ACROSS THE TN VALLEY AND INTO
PORTIONS OF THE LOWER MS VALLEY. CONVECTION ALONG THIS CORRIDOR
SHOULD BE DISORGANIZED AND PULSE IN NATURE...HOWEVER LINGERING
HIGH MOISTURE AND INSTABILITY WILL SUPPORT HEAVY RAINFALL RATES
AND A LOCALIZED FLASH FLOOD RISK WHERE CELL MERGERS OCCUR.
THE SLIGHT RISK ACROSS PORTIONS OF THE DAKOTAS INTO MN STILL LOOKS IN
GOOD SHAPE, AND SO ONLY MINOR ADJUSTMENTS WERE MADE.
CHENARD
..PREVIOUS DISCUSSION
..NORTHERN PLAINS
DURING THIS PERIOD A SHORTWAVE ROUNDING THE RIDGE ANCHORED OVER THE
FOUR CORNERS WILL MAKE ITS WAY THROUGH CENTRAL MONTANA TO WESTERN
MINNESOTA. THIS SHORTWAVE WILL DRIVE DOWNSTREAM PVA AND HEIGHT
FALLS WHILE CONCURRENT BUT MODEST RRQ DIFFLUENCE IN THE TAIL OF A
DISTANT JET STREAK HELPS ENHANCE SYNOPTIC LIFT. AT THE SURFACE, A
WAVERING BOUNDARY WITH A WAVE OF LOW PRESSURE MOVING ALONG IT WILL
TRY TO SHIFT NORTH IN RESPONSE TO SUBTLY INCREASING SOUTHERLY LOW-
LEVEL FLOW, WITH THE RESULTING ISENTROPIC ASCENT AIDING LIFT ACROSS
THE REGION. THIS ROBUST ASCENT WILL ACT UPON PWS THAT WILL SURGE
TO 1.25 TO 1.75 INCHES, OR AROUND +2 SIGMA, COLLOCATED WITH A PLUME
OF MUCAPE EXCEEDING 2000 J/KG.
AREAL COVERAGE OF CONVECTION WILL INCREASE THROUGH THE DAY,
TRACKING FROM WEST TO EAST. THE ENVIRONMENT WILL BE FAVORABLE FOR
BACKBUILDING OR TRAINING. HOURLY RAINFALL AS MUCH AS 0.75"-1.0"+
IS LIKELY, WHICH COULD CREATE LOCALLY 2-3" OF RAINFALL AS REFLECTED
BY MODEST (5-15% CHANCE) OF 3"/24 HRS. SOILS ACROSS THIS PART OF
THE COUNTRY HAVE BEEN RECENTLY WET THUS INCREASING SENSITIVITY. A
SLIGHT RISK REMAINS IN EFFECT FROM THE EASTERN DAKOTAS TO WESTERN
WISCONSIN. A BROAD MARGINAL RISK EXTENDS FROM EASTERN MONTANA TO
NORTH-CENTRAL WISCONSIN.
..MID-ATLANTIC STATES
MUCH OF THIS REGION WILL CONTINUE TO HAVE SCATTERED TO WIDESPREAD
THUNDERSTORMS AS WEAK IMPULSES TRAVERSE THROUGH THE TROUGH
OVERHEAD. IN GENERAL, THESE STORMS SHOULD BE OF THE PULSE VARIETY
AND MOVE E/NE ON 15 KTS OF 0-6KM MEAN WIND. HOWEVER, THE IMPRESSIVE
THERMODYNAMICS IN PLACE (PWS OVER 1.75 INCHES OVERLAPPING MUCAPE
OF 1000-2000 J/KG) WILL SUPPORT RAINFALL RATES OF 1-2"/HR, THROUGH
WHICH ANY SHORT-TERM TRAINING OR REPEATING ROUNDS COULD LEAD TO
INSTANCES OF FLASH FLOODING.
..EASTERN MASSACHUSETTS & RHODE ISLAND
A WAVE OF LOW PRESSURE WILL BE TRACKING SOUTH OF RHODE ISLAND
DURING THIS PERIOD KEEPING SOME SHOWERS AND THUNDERSTORMS IN PLACE
ACROSS SOUTHERN NEW ENGLAND. ALTHOUGH NEW ACCUMULATIONS ARE
EXPECTED TO BE MODEST HOURLY RATES OF 1+ INCHES/HR WILL BE
POSSIBLE. A MARGINAL RISK AREA WAS MAINTAINED FOR THIS PERIOD.
WEISS/CAMPBELL
DAY 3
VALID 12Z WED JUL 08 2026 - 12Z THU JUL 09 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE UPPER MISSISSIPPI VALLEY/UPPER GREAT LAKES...
THE SLIGHT RISK OVER THE UPPER MIDWEST STILL LOOK PRETTY GOOD,
ALTHOUGH WE DID NUDGE IT A BIT SOUTH WITH THIS UPDATE. CONVECTION
SHOULD BE ONGOING AT 12Z WEDNESDAY MOVING FROM WEST TO EAST ACROSS
MN AND WI. WHILE THIS ACTIVITY COULD BE MOVING ALONG AND WEAKENING
DURING THE MORNING, WE SHOULD SEE RENEWED DEVELOPMENT ALONG THE
FRONT BY AFTERNOON FROM SOUTHEAST MN INTO WI. APPROACHING SHORTWAVE
ENERGY AND AN UPPER LEVEL JET WILL HELP DRIVE THIS UPTICK IN
ACTIVITY, WITH PWS ABOVE THE CLIMATOLOGICAL 90TH PERCENTILE AND
CAPE APPROACHING 2000 J/KG SUPPORTING HEAVY RAINFALL RATES. WHILE A
PROGRESSIVE SQUALL LINE SHOULD EVENTUALLY EVOLVE, THERE WILL BE AN
OPPORTUNITY FOR SOME TRAINING AND BACKBUILDING DURING THE
DEVELOPMENT AND INITIAL UPSCALE GROWTH PHASE OF CONVECTION.
RAINFALL TOTALS OF 1-2" SHOULD BE MOST COMMON, BUT LOCALIZED SWATHS
OVER 3" ARE PROBABLE AND SUPPORTED BY THE 12Z RRFS.
A MARGINAL RISK WAS ADDED ACROSS PORTIONS OF THE OH/TN VALLEY INTO
THE MID-ATLANTIC. A SHORTWAVE MOVING ACROSS KY/TN AND A LINGERING
BACKDOOR FRONT OVER WV/VA SHOULD BOTH ACT AS A FOCUS FOR
CONVECTIVE DEVELOPMENT WEDNESDAY. NOT EXPECTING ANYTHING TOO
ORGANIZED OR WIDESPREAD, BUT ENOUGH MOISTURE AND INSTABILITY WILL
BE AROUND TO SUPPORT LOCALLY HEAVY RAINFALL RATES.
CHENARD
DAY 4 AND DAY 5
VALID 12Z THU JUL 09 2026 - 12Z SAT JUL 11 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE OHIO VALLEY AND CENTRAL APPALACHIANS ON DAY 5...
20Z UPDATE: ADDITIONAL INFORMATION PROVIDED ON AN UPGRADE FOR THE
D5 PERIOD WITH A MAINTENANCE OF A BROAD MRGL FOR D4, BELOW.
STRONGER FLOW WILL INITIALLY REMAIN ALONG THE NORTHERN TIER OF THE
CONUS EARLY TO MID-WEEK WITH MEAN UPPER-RIDGING ACROSS THE WESTERN
TO CENTRAL U.S. EMBEDDED SHORTWAVES ROUNDING THE UPPER-RIDGE WILL
EVENTUALLY LEAD TO DEEPENING TROUGHING ACROSS THE THE MIDWEST AND
ADJACENT AREAS ON THURSDAY. THE SOUTHWARD SHIFT OF STRONGER FLOW
ALOFT INTO THE CENTRAL PLAINS EAST THROUGH THE MIDDLE
MISSISSIPPI/OHIO/TENNESSEE VALLEYS AND LOWER GREAT LAKES WILL BRING
MORE SCATTERED THUNDERSTORM CHANCES ACROSS THE REGION.
SEASONABLY HIGH INSTABILITY AND MOISTURE POOLING ALONG A SOUTHWARD
PROGRESSING, WAVY COLD FRONT WILL SUPPORT LOCALLY HEAVY RAINFALL
BRINGING THE THREAT FOR AT LEAST ISOLATED INSTANCES OF FLASH
FLOODING, AND A BROAD MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS
FOR D4 (THURSDAY) WITH ENOUGH CONFIDENCE TO UPGRADE A LARGE PORTION
OF THE OHIO VALLEY AND CENTRAL APPALACHIANS TO A SLGT RISK FOR D5
(FRIDAY) AS INCREASING LOW-LEVEL CONVERGENCE AMPLE MID-LEVEL ASCENT
WILL LIKELY TRIGGER WIDESPREAD CONVECTION WITH TRAINING POTENTIAL
OVER THE REGION, COMPOUNDING WITH ANY IMPACTS FROM CONVECTION THE
PREVIOUS FORECAST PERIOD. CONSENSUS GREW OVER THE PAST SERIES OF
NWP UPDATES WITH THE ENSEMBLE MEAN QPF STRUCTURE SIGNALING A LARGE
AREA OF 1-2" AREAL AVERAGE TOTALS WITH EMBEDDED HIGHER AMOUNTS
POSITIONED OVER THE SOUTHERN-THIRD OF IL/IN/OH THROUGH MUCH OF KY
INTO WV. THIS IS COINCIDENT WITH THE PROGRESSION OF BOTH THE FRONT
AND A STRENGTHENING SHORTWAVE TROUGH MIGRATING OUT OF THE CENTRAL
PLAINS INTO THE REGION AS WE MOVE INTO FRIDAY. ML OUTPUT IS ALSO
FAVORING THE OHIO RIVER BASIN INTO THE CENTRAL APPALACHIANS
EXTENDED FROM SOUTHWESTERN PA DOWN THROUGH WV AS TERRAIN INFLUENCES
ALONG WITH THE SYNOPTIC EVOLUTION WILL COUPLE INTO A TARGETED
THREAT FOR HEAVY RAINFALL AND LOCAL MAXIMA SUFFICIENT FOR SCATTERED
FLASH FLOOD PROSPECTS. PQPF FORECAST FOR AT LEAST 1" SIGNALS A
BROAD 20-40% PROBABILITY WITH A BULLSEYE OF 50-80% LOCATED OVER THE
CENTRAL APPALACHIAN FRONT IN NORTHERN WV. THIS IS A RELATIVELY
BULLISH SIGNATURE AT THIS LEAD, ENOUGH TO WARRANT AN UPGRADE TO A
SLGT RISK OVER THE AFOREMENTIONED AREAS FROM IL TO WV.
PUTNAM/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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