688
FOUS30 KWBC 041549
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1149 AM EDT SAT JUL 4 2026
DAY 1
VALID 16Z SAT JUL 04 2026 - 12Z SUN JUL 05 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS EASTERN
KANSAS AND OKLAHOMA AND PORTIONS OF NORTHERN ILLINOIS AND INDIANA...
16Z UPDATE:
MUCH OF THE CENTRAL TO EASTERN U.S. IS IN A WARM, MOIST, AND
UNSTABLE AIR MASS, ALL AHEAD OF A SLOWLY SOUTHWARD FRONTAL BOUNDARY
THAT IS CURRENTLY DRAPED ACROSS PORTIONS OF THE UPPER MIDWEST TO
GREAT LAKES. SEVERAL ORGANIZED CLUSTERS OF THUNDERSTORMS ONGOING
THIS MORNING WILL BE THE FOCUS FOR POCKETS OF HEAVY RAINFALL AND
INSTANCES OF FLASH FLOODING.
ONGOING CONVECTION ACROSS EASTERN KANSAS THIS MORNING SHOULD
EVENTUALLY SUBSIDE BY EARLY AFTERNOON, BUT RENEWED CONVECTION LATER
THIS EVENING JUST SOUTH OF THAT ALONG THE RESIDUAL BOUNDARY WILL BE
THE FOCUS FOR HEAVY RAINFALL LATER IN THE PERIOD. NO SIGNIFICANT
ADJUSTMENTS WERE MADE TO THE SLIGHT RISK AREA THERE, WITH
PROBABILITIES REMAINING HIGH FOR LOCALIZED 3-5" TOTALS THROUGH
EARLY SUNDAY MORNING.
ANOTHER VORT MAX MOVING INTO ILLINOIS THIS MORNING WILL COINCIDE
WITH PEAK HEATING OVER NORTHERN ILLINOIS AND WEST-CENTRAL INDIANA
TO GENERATE ANOTHER ROUND OF THUNDERSTORMS CAPABLE OF PRODUCING
HEAVY RAINFALL. POCKETS OF 2-4" TOTALS WILL BE POSSIBLE BASED OFF
THE LATEST HREF AND 12Z HI-RES MODELS ARE IN REASONABLE AGREEMENT
FOR THE PLACEMENT OF THIS NEXT ROUND OF HEAVY RAINFALL. THROUGH
COORDINATION WITH WFO LOT AND SURROUNDING OFFICES, A SLIGHT RISK
WAS INTRODUCED WITH THIS UPDATE MAINLY FOR THE AFTERNOON TO EARLY
EVENING HOURS WHERE SCATTERED INSTANCES OF FLASH FLOODING ARE
EXPECTED.
ELSEWHERE ACROSS THE EASTERN U.S., ISOLATED TO SCATTERED
THUNDERSTORMS ARE EXPECTED AND WILL BE A FLASH FLOOD CONCERN FOR
MAINLY URBAN, LOW-LYING, AND OTHER SENSITIVE AREAS. SOME CONCERN
FOR THE I-95 CORRIDOR FROM DC TO NYC TODAY, PARTICULARLY ACROSS
NORTHERN NJ WHERE GUIDANCE IS A BIT MORE BULLISH. FOR NOW, HAVE
KEPT THE RISK CATEGORY AT MARGINAL AS STORMS MAY BE MORE
PROGRESSIVE.
TAYLOR
---PREVIOUS DISCUSSION---
OVERNIGHT CONVECTION OVER THE HIGH PLAINS SHOULD PERSIST AND
POSSIBLY GROW UPSCALE AS IT MOVES EASTWARD ACROSS NEBRASKA AND
KANSAS. INCREASING CONFIDENCE IN THE GENERATION OF AN MCS
ACROSS THE CENTRAL PLAINS, MOVING SOUTHEAST INTO THE LOWER
MISSISSIPPI VALLEY SATURDAY EVENING IN CONJUNCTION WITH A COLD
FRONT APPROACH FROM THE NORTH AND SURFACE LOW POSITIONED OVER THE
ADJACENT SOUTHERN PLAINS. INCREASING LOW-LEVEL CONVERGENCE AHEAD
OF THE APPROACHING FRONT WILL HELP SUSTAIN/ENHANCE CONVECTION.
LOW-LEVEL FLOW WILL BECOME BACKED FOR A TIME ACROSS THE AREA OF
SOUTHEAST KS INTO NORTHEASTERN OK AHEAD OF THE FRONT ACCORDING TO
FORECAST SOUNDINGS FROM VARIOUS DETERMINISTIC CAMS. THIS LEADS TO
EFFECTIVE BOUNDARY LAYER SHEAR APPROACHING 35-40KTS WILL BE
EFFICIENT IN SUSTAINING STRONGER UPDRAFTS AND MESOCYCLONE
FORMATIONS CAPABLE OF STRONG TO SEVERE CELLS, EVEN IN THE CASE OF
CELL MERGERS. PWATS BETWEEN 1.8-2.1" ARE EXPECTED IN THE AREA OF
INTEREST ALLOWING FOR A DEEP MOIST PROFILES SUITABLE FOR HEAVY RAIN
CORES. HREF PROBS FOR >1"/HR RATES ARE ACTUALLY PROLONGED WITHIN
THE TEMPORAL ASPECT OF THE FORECAST OVER THE REGION WITH A SOLID
30-50% PROB FROM 00Z-12Z SATURDAY ACROSS THE AFOREMENTIONED AREA
MEANING SOME BACK-BUILDING BEHIND ANY ORGANIZED CONVECTIVE PATTERN
IS PLAUSIBLE. MODEST 30-50% PROBS FOR >3" EXIST OVER THE AREA FROM
I-70 WEST OF KANSAS CITY DOWN THROUGH TULSA WITH THE HIGHEST PROBS
LOCATED OVER NORTHEAST OKLAHOMA. ISOLATED LOW-END PROBS FOR >5"
ALSO EXIST, BUT ARE GENERALLY NOTING THE TOP-END OF THE POTENTIAL
FOR THE THREAT AS THE PROGRESSION OF THE MCS SHOULD LIMIT THE
PROSPECT FOR MORE APPRECIABLE IMPACTS/COVERAGE. A SLIGHT RISK WAS
MAINTAINED ALTHOUGH MODESTLY SHIFTED SOUTHWARD COVERING SOUTHEAST
KANSAS AND NORTHEAST OKLAHOMA.
..MIDWEST INTO THE MID ATLANTIC
PULSE CONVECTION EXPECTED OVER A VAST AREA SPANNING FROM THE
CENTRAL/NORTH-CENTRAL STATES TO THE MID-ATLANTIC/NORTHEAST REGIONS
AS SHORTWAVE ENERGIES MOVE THROUGH THE FLOW. ANY THUNDERSTORM WILL
BE CAPABLE OF PRODUCING LOCAL RATES OF 1-2"/HR WHICH COULD RESULT
IN ISOLATED CASES OF FLASH FLOODING OVER A BROAD AREA WITH THE
FOCUS LIKELY WITHIN ANY URBAN CORRIDORS OR COMPLEX TERRAIN
(APPALACHIA). A BROAD MARGINAL RISK WAS MAINTAINED OVER THE ABOVE
REGIONS TO ACCOUNT FOR THE THREAT.
KLEEBAUER/CAMPBELL
DAY 2
VALID 12Z SUN JUL 05 2026 - 12Z MON JUL 06 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE MID-ATLANTIC...
AN EAST-WEST ORIENTATED FRONT BOUNDARY WILL BE SPRAWLED ACROSS THE
NORTHEAST/NORTHERN MID-ATLANTIC REGION DURING THIS PERIOD. MODERATE
INSTABILITY COMBINED WITH PW VALUES OF 2+ INCHES ARE EXPECTED TO
OVERLAP NEAR THE FRONTAL BOUNDARY TO PRODUCE PERIODS OF HEAVY
RAINFALL. THIS AREA HISTORICALLY IS MORE PRONE TO FLASH FLOODING
DUE TO TERRAIN INFLUENCES AND MORE SENSITIVE HYDROLOGIC SCHEMES
THUS MAINTAINING THE SLIGHT RISK FOR EXCESSIVE RAINFALL FOR THIS
PART OF THE REGION. BACKBUILDING AND TRAINING OF THUNDERSTORMS MAY
BE POSSIBLE. SCATTERED FLASH FLOOD CONCERNS EXIST OVER THE CENTRAL
MID- ATLANTIC WITH AN INCREASING RISK OF HEAVY CONVECTION OVER
PORTIONS OF PENNSYLVANIA DOWN THROUGH THE WASHINGTON DC-
BALTIMORE- PHILADELPHIA CORRIDOR. A BROAD MARGINAL RISK AREA SPANS
FROM EASTERN OKLAHOMA/KANSAS EASTWARD TO THE MID- ATLANTIC/SOUTHERN
PORTIONS OF THE NORTHEAST.
KLEEBAUER/CAMPBELL
DAY 3
VALID 12Z MON JUL 06 2026 - 12Z TUE JUL 07 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE MID-ATLANTIC/NORTHEAST ON MONDAY...
THE THREAT FOR EXCESSIVE RAINFALL AND SCATTERED AREAS OF FLASH
FLOODING WILL REMAIN FOR PORTION OF THE MID-ATLANTIC FOR THIS
PERIOD. RAINFALL OCCURRING DURING THE DAY 1 AND DAY 2 PERIODS MAY
LEAD TO INCREASED SOIL SATURATION AND LOWERED FLASH FLOOD GUIDANCE
FOR THIS REGION, THUS MAKING IT MORE SENSITIVE FOR ADDITIONAL HEAVY
RAINFALL. NEAR AND JUST SOUTH OF THIS FRONT INSTABILITY OF 2000
J/KG OR GREATER AND PWS OVER 2" ARE FORECAST, AN ENVIRONMENT
SUPPORTING EFFICIENT RAINFALL AND HIGH HOURLY RATES.
STRONGER LOW LEVEL CONVERGENCE WILL BE CAPABLE OF PRODUCING A
BROADER AREA OF MODERATE TO LOCALLY HEAVY RAINFALL ACROSS NEW YORK
INTO SOUTHERN NEW ENGLAND.; HOWEVER, WITH LESS AVAILABLE
INSTABILITY RAINFALL RATES WILL LIKELY NOT PEAK AS HIGH AS THOSE
FURTHER SOUTH. THUS, THIS AREA IS COVERED BY A BROAD MARGINAL RISK
FROM PORTIONS OF UPSTATE NEW YORK TO THE CAPE, SOUTH TO THE
CAROLINAS AND THEN SOUTHWEST INTO ARKANSAS AND NORTHERN LOUISIANA.
CHENARD/CAMPBELL
DAY 4 AND DAY 5
VALID 12Z TUE JUL 07 2026 - 12Z THU JUL 09 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE NORTHERN PLAINS TO UPPER GREAT LAKES TUESDAY AND WEDNESDAY...
SLIGHT RISKS OF EXCESSIVE RAINFALL HAVE BEEN INTRODUCED ACROSS
PORTIONS OF THE NORTHERN PLAINS INTO THE UPPER GREAT LAKES
TUESDAY-WEDNESDAY. A SEASONABLY MOIST, UNSTABLE AIRMASS WILL BE IN
PLACE ALONG THE NORTHERN SIDE OF AN UPPER-RIDGE BUILDING OVER THE
WESTERN TO CENTRAL U.S. EARLY NEXT WEEK. AN UPPER-LEVEL WAVE
ROUNDING THE RIDGE WILL HELP TRIGGER SCATTERED TO WIDESPREAD
THUNDERSTORM DEVELOPMENT AT THE LEADING EDGE OF THE DEEPER MOISTURE
OVER THE NORTHERN HIGH PLAINS. PROPAGATION AHEAD OF A DEVELOPING
SURFACE WAVE ALONG A QUASI-STATIONARY FRONTAL BOUNDARY AND
DEVELOPING LOW-LEVEL JET WILL HELP MAINTAIN STORMS INTO THE
OVERNIGHT HOURS THROUGH THE NORTHERN PLAINS WITH THE POTENTIAL FOR
AT LEAST ORGANIZED CLUSTERS OF STORMS IF NOT A MESOSCALE
CONVECTIVE SYSTEM. A SIMILAR SCENARIO WILL PLAY OUT WEDNESDAY AS
ONGOING/RENEWED STORM DEVELOPMENT WILL CONTINUE EASTWARD INTO THE
UPPER GREAT LAKES. TYPICAL UNCERTAINTY ON THE EXACT LOCATION AND
COVERAGE OF CONVECTIVE DEVELOPMENT REMAINS A CONCERN PARTICULARLY
AS THE STORM EVOLUTION TUESDAY WILL LIKELY IMPACT STORM
DEVELOPMENT/EVOLUTION WEDNESDAY. HOWEVER, GOOD CONSENSUS AMONGST
THE DETERMINISTIC MODEL GUIDANCE ON AREAL AVERAGE TOTALS IN THE
1-2" RANGE AND LOCALLY HIGHER AMOUNTS OF 3-4" SUPPORTS THE THREAT
FOR SCATTERED FLASH FLOODING WITH POTENTIAL AREAL ADJUSTMENT OF
THE RISK IN SUBSEQUENT OUTLOOKS.
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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