106
FOUS30 KWBC 061605
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1205 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...
..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...
..NORTHERN/CENTRAL PLAINS TO THE UPPER GREAT LAKES
SCATTERED TO WIDESPREAD CONVECTION WILL BREAK OUT ACROSS THE
NORTHERN/CENTRAL PLAINS TO THE MIDWEST ALONG AND AHEAD OF AN EASTWARD
TRACKING FRONTAL BOUNDARY. THE EXACT LOCATION OF THE HIGHEST QPF
REMAINS UNCERTAIN HOWEVER THE LATEST GUIDANCE AGREES ON AREAL
AVERAGE OF 1-2 INCHES WITH ISOLATED MAXIMUMS OF 3+ INCHES WILL
OCCUR FROM EASTERN MINNESOTA TO UPPER MICHIGAN/NORTHERN WISCONSIN.
RECENT RAINFALL WILL KEEP SOME LOCATIONS SENSITIVE TO ADDITION
HEAVY RAINFALL. A SLIGHT RISK WAS MAINTAINED FOR THESE AREAS. A
BROAD MARGINAL SPANS FROM EASTERN NEBRASKA/NORTHERN KANSAS TO THE
GREAT LAKES.
CAMPBELL
DAY 4 AND DAY 5
VALID 12Z THU JUL 09 2026 - 12Z SAT JUL 11 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE CENTRAL PLAINS TO MIDWEST...
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 BROAD MARGINAL RISKS OF EXCESSIVE RAINFALL HAVE BEEN
OUTLINED FOR THURSDAY AND FRIDAY. ONE OR MORE SLIGHT RISKS MAY
EVENTUALLY BE NECESSARY WITH MORE CONFIDENCE IN THE FRONTAL
POSITION AS STORM MOTIONS MAY TEND TO RUN GENERALLY PARALLEL TO THE
BOUNDARY HELPING TO LEAD TO PROLONGED/REPEATED ROUNDS OF RAINFALL.
MESOSCALE CONVECTIVE SYSTEMS WILL ALSO BE A CONCERN AS THE UPPER-
FLOW SHIFTS NORTHWESTERLY, WITH AT LEAST ONE SIGNAL FOR ORGANIZED
CONVECTION NOTABLE IN THE GUIDANCE MOVING OFF THE CENTRAL HIGH
PLAINS ON THURSDAY.
PUTNAM
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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