929
FOUS30 KWBC 292001
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
401 PM EDT WED JUL 29 2026
DAY 1
VALID 16Z WED JUL 29 2026 - 12Z THU JUL 30 2026
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR THE
BERKSHIRES AND SURROUNDING AREAS...
..16Z UPDATE
THE MODERATE RISK WAS TRIMMED FROM THE EAST ACROSS CENTRAL
MASSACHUSETTS AND EASTERN CONNECTICUT WITH THIS UPDATE. WHILE RAIN
IS ONGOING IN MOST OF THESE AREAS, THE AREA DIDN'T SEE ANYWHERE
NEAR AS MUCH RAIN AS AREAS FURTHER WEST FROM THE BERKSHIRES TO THE
HUDSON VALLEY, SO THE AREA REMAINS IN A SLIGHT.
THE MARGINAL AND SLIGHT RISK AREAS WERE TRIMMED ON THE SOUTHERN END
ALONG LONG ISLAND SOUND (INCLUDING NYC), AS THE STEADIEST RAINS IN
THAT AREA HAVE ENDED. SCATTERED SHOWERS CAN'T BE RULED OUT, BUT
EVEN IN URBAN AREAS SHOULD NOT PRODUCE ENOUGH RAIN TO CAUSE EVEN
ISOLATED FLASH FLOODING.
MINOR TWEAKS WERE MADE TO OTHER PORTIONS OF THE NORTHEAST.
OUT WEST, THE MARGINAL RISK WAS EXTENDED NORTHWEST TO INCLUDE THE
MISSOURI RIVER VALLEY IN EASTERN NEBRASKA AND KANSAS, AS WELL AS
WESTERN IOWA AND MISSOURI, INCLUDING THE KC METRO. THIS IS
PRIMARILY FOR HEAVY BUT SLOW MOVING STORMS THAT HAVE DEVELOPED IN
THIS AREA FROM AN OVERNIGHT MCS.
FINALLY, THE SLIGHT RISK IN COLORADO WAS EXPANDED SOUTH TO INCLUDE
THE EXTREME NORTHEASTERN FRINGE OF NEW MEXICO, WHERE AFTERNOON
SHOWERS AND THUNDERSTORMS THAT WILL BE AT LEAST INITIALLY TIED TO
THE TERRAIN MAY CAUSE WIDELY SCATTERED INSTANCES OF FLASH FLOODING.
WEGMAN
..PREVIOUS DISCUSSION
..NORTHEAST
INTENSE RAINFALL WILL BE ON-GOING OVER PORTIONS OF THE NORTHEAST AS
THE DAY 1 PERIOD BEGINS AT 29/12Z, WITH SOME TRAINING OF CELLS AND
SOME PLACES EXPERIENCING MULTIPLE ROUNDS OF HEAVY RAINFALL--PARTICULARLY
ACROSS WESTERN MASSACHUSETTS, FAR SOUTHERN VERMONT, AND BROADLY
ACROSS SOUTHERN NEW ENGLAND. RAINFALL RATES BETWEEN 1-2"/HR AT
TIMES WILL BE POSSIBLE THROUGH LATE MORNING/EARLY AFTERNOON AND
TOTALS OF 2-4" (WITH LOCALIZED HIGHER AMOUNTS POSSIBLE) ARE
EXPECTED.
HREF/RRFS NEIGHBORHOOD PROBABILITIES FROM THE 29/00Z RUNS REMAINED
HIGH (GREATER THAN 80 PERCENT) FOR 3" TOTALS ACROSS
WESTERN/CENTRAL MA INTO FAR SOUTHERN VT. PROBABILITIES ARE MODERATE
(30-50 PERCENT) FOR 5" TOTALS.
GIVEN THE SETUP AND RISK OF SIGNIFICANT FLASH FLOODING CONTINUING
FROM THE DAY 1 PERIOD, A MODERATE RISK WAS MAINTAINED WITH FEW
CHANGES GIVEN THE CUMULATIVE RAINFALL AMOUNTS. AFTER 30/00Z...THE
INTENSITY OF RAINFALL SHOULD SUBSIDE WHILE ALSO SHIFTING EASTWARD.
..FOUR CORNERS STATES INTO THE CENTRAL/NORTHERN PLAINS
MONSOONAL FLOW PERSISTS WITH ISOLATED TO WIDELY SCATTERED
CONVECTION EXTENDING FROM THE FOUR CORNERS REGION NORTHWARD AND
EASTWARD...PERHAPS EXTENDING AS FAR EAST AS THE PLAINS OF COLORADO.
SOME OF THIS RAIN COULD FALL ATOP SOILS SATURATED FROM HEAVY RAIN
PRIOR TO THE START OF THE DAY 1 PERIOD AT 29/12Z. PERSISTENCE IN
THE PATTERN AND MOISTURE DISTRIBUTION LEAVES THE RISK AREA IN GOOD
SHAPE WITH THE SLIGHT RISK FOCUSED ON EASTERN COLORADO.
..CENTRAL GULF COAST REGION INTO PARTS OF THE SOUTHEAST
A COLD FRONT STALLING ALONG THE GULF COAST WILL BE A FOCUS FOR SLOW
MOVING AND TRAINING THUNDERSTORMS TODAY INTO TONIGHT. GUIDANCE
CONTINUES TO INDICATE A LOW-PROBABILITY THREAT FOR AT LEAST 3" OF
RAIN DUE TO TRAINING OF 1-2"/HR RAIN RATES WITHIN FAVORABLE
THERMODYNAMICS. THIS REGION CAN GENERALLY TOLERATE SIGNIFICANT RAIN
RATES AND THIS AMOUNT OF RAINFALL, BUT ANY MORE PRONOUNCED
TRAINING COULD RESULT IN ISOLATED FLASH FLOOD RELATED IMPACTS.
TAYLOR/BANN
DAY 2
VALID 12Z THU JUL 30 2026 - 12Z FRI JUL 31 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE MID TO LOWER MISSOURI AND MID TO UPPER MISSISSIPPI VALLEYS...
..2030Z UPDATE
NO MAJOR CHANGES WERE NEEDED WITH THIS AFTERNOON'S UPDATE. THE
SLIGHT RISK OVER THE PLAINS AND MIDWEST WAS EXPANDED WESTWARD WITH
THE LATEST UPDATE DUE TO GUIDANCE MOVING THE AREA OF HEAVIEST
RAINFALL WESTWARD AS COMPARED TO PRIOR FORECASTS. OTHERWISE, FEW
CHANGES WERE NEEDED. THE HEAVIEST RAINS THROUGH THE PERIOD CONTINUE
TO BE FORECAST FROM NORTHEASTERN NEBRASKA THROUGH SOUTHWESTERN
MINNESOTA.
STORM COVERAGE AND INTENSITY ACROSS THE 4 CORNERS REGION APPEARS
SIGNIFICANTLY MUTED AS COMPARED WITH PREVIOUS DAYS. THE MARGINAL
RISK IN THE AREA WAS TRIMMED BACK TO PORTIONS OF ARIZONA AND NEW
MEXICO AS A RESULT.
A MOISTURE FEED FROM THE GULF WILL ALLOW FOR A FEW STORMS TO FORM
OVER WESTERN ARKANSAS AND INTO THE LOWER MISSISSIPPI VALLEY. THE
MARGINAL RISKS WERE COMBINED ALONG THE FRONT.
LINGERING MOISTURE ALONG THE NEW ENGLAND COAST COULD CONTINUE TO
POSE AN ISOLATED FLASH FLOODING THREAT, SO THE MARGINAL WAS
MAINTAINED AND EXPANDED A BIT OVER SOUTHEASTERN MASSACHUSETTS,
RHODE ISLAND, AND EASTERN CONNECTICUT.
WEGMAN
..PREVIOUS DISCUSSION
..LOWER MISSOURI VALLEY INTO THE MID-UPPER MISSISSIPPI VALLEY
SHORTWAVE ENERGY WILL BE PROGRESSING EAST SOUTHEAST AS IT TRACKS
ACROSS PARTS OF THE CENTRAL AND NORTHERN PLAINS ON THURSDAY INTO
THURSDAY NIGHT/EARLY FRIDAY MORNING. THE SHORTWAVE ENERGY WILL BE
ENCOUNTERING AN INCREASINGLY MOIST AND UNSTABLE AIRMASS WITH
PRECIPITABLE WATER VALUES IN EXCESS OF 2 INCHES BEING DRAWN INTO
THE REGION AHEAD OF THE SHORTWAVE. GIVEN THE MCS/UPSCALE GROWTH
POTENTIAL WITH THIS SYSTEM, CONCENTRATED AREAS OF HEAVY RAIN ARE
EXPECTED GIVEN THE POTENTIAL FOR TRAINING AND REPEAT-CONVECTION. THE
SLIGHT RISK REMAINED IN GOOD SHAPE AND ONLY MINOR ADJUSTMENTS WERE
NEEDED TO COVERS THE 29/00Z ENSEMBLE GUIDANCE AND TO ACCOUNT FOR
THE UNCERTAINTY/SPREAD AMONG THE MODELS.
..FOUR CORNERS STATES INTO THE CENTRAL/NORTHERN PLAINS
MONSOONAL FLOW AND ANOMALOUS DEEP-LAYER MOISTURE WILL MAINTAIN AN
ISOLATED EXCESSIVE RAINFALL RISK EXTENDING FROM EASTERN ARIZONA
NORTHEASTWARD ACROSS MUCH OF WESTERN AND NORTHERN NEW MEXICO INTO
PARTS OF COLORADO. THE EXPANDING MID/UPPER LEVEL RIDGE WILL LIKELY
LIMIT THE COVERAGE COMPARED TO RECENT DAYS.
..CENTRAL GULF COAST REGION INTO PARTS OF THE SOUTHEAST
HEAVY RAINFALL IS EXPECTED ALONG A FRONT ASSOCIATED WITH A LOW
PRESSURE SYSTEM WHICH WILL BE PULLING AWAY FROM NEW ENGLAND.
HEAVY RAINFALL WITH SOME POTENTIAL OF FLOODING WILL BE FOCUSED
ALONG AND NEAR THE FRONT...ESPECIALLY OVER PARTS OF FLORIDA AND
GEORGIA NEAR THE STATE LINE.
..NEW ENGLAND
THE DEPARTING LOW PRESSURE IS EXPECTED TO BE ACROSS EASTERN MA AT
THE START OF THE PERIOD AND TRANSITION OFF THE COAST DURING THE
PERIOD. LOCALLY HEAVY RAINFALL WILL REMAIN POSSIBLE ACROSS THE
REGION GIVEN ITS PROXIMITY AND AMPLE MOISTURE TO WORK WITH. WHILE
THE INSTABILITY WILL LIKELY BE LESS COMPARED TO TUESDAY/WEDNESDAY,
THE STRONGER DYNAMICS AT PLAY AND POTENTIAL FOR TRAINING RAINFALL
COULD LEAD TO A LOCALIZED THREAT, PARTICULARLY IF OVER AREAS MORE
SATURATED FROM PREVIOUS RAINFALL. A MARGINAL RISK WAS MAINTAINED.
TAYLOR/BANN
DAY 3
VALID 12Z FRI JUL 31 2026 - 12Z SAT AUG 01 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FRIDAY ACROSS
PARTS OF THE UPPER MIDWEST TO MID MISSISSIPPI VALLEY...
..2030Z UPDATE
A SMALL INCREASE IN COVERAGE OF HEAVY RAIN ACROSS THE MID-
MISSISSIPPI VALLEY LED TO A SMALL EXPANSION OF THE SLIGHT TO COVER
PORTIONS OF EASTERN MISSOURI AND WESTERN KENTUCKY WITH THIS UPDATE.
THE HEAVIEST RAINS CONTINUE TO BE FOCUSED INTO FAR EASTERN IOWA,
NORTHWESTERN ILLINOIS AND SOUTHWESTERN WISCONSIN, WHERE NO CHANGES
WERE MADE AS THE FORECAST REMAINS ON TRACK.
ELSEWHERE, SOME SMALL ADJUSTMENTS OF THE MRGL TO REMOVE PORTIONS OF
NORTHWESTERN NEW MEXICO AND INCLUDE MORE OF THE TEXAS PANHANDLE
WERE MADE, BUT TOTAL COVERAGE AND INTENSITY OF STORMS IN THESE
AREAS REMAINS LITTLE CHANGED.
WEGMAN
..PREVIOUS DISCUSSION
CENTRAL US SYSTEM...
SHORTWAVE ENERGY INITIALLY MOVING EASTWARD OUT OF THE NORTHERN
ROCKIES AND ADJACENT HIGH PLAINS WILL BE ACCOMPANIED BY SHOWERS AND
THUNDERSTORMS ON FRIDAY MORNING. THE FLOW PATTERN ON THE NORTHERN
PART OF THE UPPER HIGH ANCHORED TO ITS WEST SHARPENS DURING THE
DAY...WHICH INDUCES A TURN TO THE SOUTH FOR THE NORTHERN PLAINS
SYSTEM. TENDED TO FOLLOW THE NUMERICAL GUIDANCE FOR PLACEMENT OF
THE MARGINAL AND SLIGHT RISK AREAS WHERE THE SYNOPTIC SCALE FORCING
IS GREATEST. THIS NECESSITATED A BIT MORE EASTWARD NUDGING FROM
THE PREVIOUS OUTLOOK. THE SOUTHERN PORTION OF THE MARGINAL RISK
AREA REMAINED CLOSER TO THE PLACEMENT OF GREATER INSTABILITY WHICH
WOULD SUPPORT HIGHER INTENSITY RAINFALL RATES. ANY DOWNPOURS ACROSS
THAT REGION MAY AT LEAST HAVE A CHANCE AT CHALLENGING THE FLASH
FLOOD GUIDANCE. BOTH THE GFS AND ECMWF PLACED THEIR AXIS OF HIGHEST
PRECIPITABLE WATER (1.8 TO 2.2 INCHES) NEAR THE MISSISSIPPI RIVER
EARLY IN THE PERIOD WHICH GETS DEFLECTED TOWARDS THE TENNESSEE
VALLEY BY EARLY SATURDAY MORNING.
..CENTRAL GULF COAST REGION INTO PARTS OF THE SOUTHEAST
LOCALLY HEAVY TO EXCESSIVE RAINFALL IS POSSIBLE IN PROXIMITY TO AN
EAST-WEST ORIENTED QUASI-STATIONARY FRONT THAT HAD BEEN ASSOCIATED
WITH A NORTHEAST US CYCLONE IN PREVIOUS DAYS. DEEP-LAYER MOISTURE
AND INSTABILITY SHOULD BE MORE THAN SUFFICIENT AND THE GUIDANCE
SHOWS SUFFICIENT EFFECTIVE BULK SHEAR (0-6KM MAGNITUDES GENERALLY
OVER 20 KTS) FOR MORE ORGANIZED/PERSISTENT CONVECTIVE ORGANIZATION.
AS A RESULT, MAINTAINED THE INHERITED MARGINAL RISK .
..FOUR CORNERS STATES INTO THE SOUTHERN-CENTRAL HIGH PLAINS
MONSOONAL FLOW AND ANOMALOUS DEEP-LAYER MOISTURE WILL KEEP THE
POTENTIAL FOR ISOLATED INSTANCES OF EXCESSIVE RAINFALL ACROSS
PORTIONS OF EASTERN AZ AND MUCH OF NEW MEXICO INTO COLORADO. THE
AREAL COVERAGE MAY BE LESS THAN IN PRECEDING DAYS GIVEN THE
EXPANSION OF THE SPRAWLING UPPER RIDGE.
BANN
DAY 4 AND DAY 5
VALID 12Z SAT AUG 01 2026 - 12Z MON AUG 03 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL SATURDAY OVER
PORTIONS OF THE OHIO AND TENNESSEE VALLEYS...
2030Z UPDATE...
EXTENDED THE DAY 4 SLIGHT RISK FARTHER SOUTH FROM THE OHIO INTO THE
TENNESSEE VALLEY. STORMS ARE EXPECTED TO DEVELOP AHEAD OF THE COLD
FRONT ASSOCIATED WITH THE SHORTWAVE TROUGH MOVING THROUGH THE
MIDWEST ON SATURDAY. THE MODEL SPREAD WITH REGARDS TO WHERE THE
BETTER FORCING WILL FOCUS AND ITS POTENTIAL IMPACT ON THE
DEVELOPMENT OF HEAVIER AMOUNTS IS NOTABLE. HOWEVER, THE 12Z
GUIDANCE PRESENTED ENOUGH OF A SIGNAL TO WARRANT EXTENDING THE
SLIGHT RISK FARTHER SOUTH. STORMS THAT DEVELOP IN THIS AREA WILL
HAVE ACCESS TO DEEPER MOISTURE (PWS ~2-2.25 INCHES) AND LIKELY
GREATER INSTABILITY, SUPPORTING HEAVY RATES.
ELSEWHERE, MADE ONLY MINOR ADJUSTMENTS TO OUTLOOK AREAS ON BOTH
DAYS.
PEREIRA
..OHIO AND TENNESSEE VALLEYS INTO PARTS OF THE SOUTHEAST
ON DAY 4 (SAT-SAT NIGHT), RATHER SIGNIFICANT CHANGES WERE MADE TO
YESTERDAY'S DAY 5 ERO, BASED ON THE LATEST GUIDANCE TRENDS.
SPECIFICALLY, THE GLOBALS AND MOST ENSEMBLES SHOW THE UPPER TROUGH
AMPLIFYING SOMEWHAT WITH THE INFLUX OF SHORTWAVE
ENERGY/CONVECTIVELY- AIDED VORT LOBES DROPPING SOUTHEAST. HOWEVER,
MOST OF THE GUIDANCE SHOW LESS AMPLIFICATION COMPARED TO LAST
NIGHT'S RUNS, WITH MORE OF A POSITIVE TO NEUTRAL TILT TO THE TROUGH
VS. NEGATIVE. THIS IN TURN IS ALLOWING FOR A MORE PROGRESSIVE
WEST-TO-EAST SHIFT IN THE PRE- FRONTAL RAINFALL EAST OF THE
MISSISSIPPI, SUPPORTED (PERHAPS LED BY) BOTH THE GFS AND ECMWF AI
MODELS. THEREFORE THE MARGINAL RISK AND ENCOMPASSING SLIGHT RISK
AREAS WERE SHIFTED EAST AS WELL, WITH THE SLIGHT RISK CONFINED TO
MAINLY THE NORTHERN AREAS (OH VALLEY INTO CUMBERLAND PLATEAU) PER
THE ECMWF AND GFS AI TRENDS, ALONG WITH THE HIGHEST 24HR QPF
EXCEEDANCE PROBABILITIES PER THE 00Z ECENS, AND WHERE THERE IS A
SIGNAL (ALBEIT WEAK) PER THE MOST RECENT ECMWF EFI. THE SLIGHT RISK
IS ALSO IN AN AREA WITH COMPARATIVELY LOWER 1/3/6 HR FFG VS. AREAS
FARTHER SOUTH.
..INTERIOR NORTHEAST
AFOREMENTIONED LONGWAVE 500 MB TROUGH DOES BEGIN TO TAKE ON A MORE
NEUTRAL TO NEGATIVE TILT ON DAY 5 (SUN-SUN NIGHT) PER BOTH THE GFS
AND ECMWF. AS THIS OCCURS, THE EASTWARD PROGRESSION OF THE
FAVORABLE PRE-TROUGH/FRONT DYNAMICAL FORCING AND ASSOCIATED
MOISTURE AXIS (PWS OF 1.75-2.00") WILL BEGIN TO SLOW CONSIDERABLY,
THEREBY ALLOWING FOR MULTIPLE ROUNDS OF MODERATE-HEAVY RAINFALL.
FOR NOW, HAVE HOISTED A MARGINAL RISK ACROSS THIS REGION ON DAY 5,
AS THE MAXIMUM 24HR DETERMINISTIC QPFS FROM THE LATEST GLOBAL RUNS
ARE STILL (FOR THE TIME BEING) UNDER 3".
..FOUR CORNERS STATES INTO THE SOUTHERN-CENTRAL HIGH PLAINS
MONSOONAL FLOW AND ANOMALOUS DEEP-LAYER MOISTURE WILL MAINTAIN A
MARGINAL (ISOLATED) EXCESSIVE RAINFALL RISK OVER EASTERN AZ AND
MUCH OF NM INTO SOUTH-CENTRAL CO ON DAY 4. BY DAY 5 (SUN-SUN
NIGHT), BOTH THE DETERMINISTIC AND PROBABILISTIC QPFS PER THE
GLOBAL AND AI GUIDANCE WOULD SUPPORT A SMALLER MGNL RISK AREA.
..CENTRAL GULF COAST REGION INTO PARTS OF THE SOUTHEAST
HEAVY RAINFALL THREAT WILL CONTINUE OVER THIS REGION ALONG THE
SOUTHERN PERIPHERY OF THE FULL-LATITUDE TROUGH, SOUTH OF THE
QUASI-SATIONARY FRONT. DEEP-LAYER MOISTURE AND INSTABILITY SHOULD
BE MORE THAN SUFFICIENT, ESPECIALLY WHEN COINCIDING WITH THE WEAK
UPPER FORCING (UPSTREAM UPPER TROUGH W/ EMBEDDED CONVECTIVELY-AIDED
SHORTWAVES), FOR MORE ORGANIZED/PERSISTENT CONVECTIVE
ORGANIZATION. AS A RESULT, HAVE MAINTAINED THE INHERITED MARGINAL
RISK ON DAY 4 (SAT-SAT NIGHT), WITH A SIMILAR MARGINAL RISK AREA
ON DAY 5 (SUN-SUN NIGHT).
HURLEY
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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