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FOUS30 KWBC 271947
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
347 PM EDT SUN JUL 27 2025
DAY 1
VALID 16Z SUN JUL 27 2025 - 12Z MON JUL 28 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE UPPER MIDWEST, NORTHERN APPALACHIANS AND PARTS OF THE NORTHEAST...
..THE EASTERN DAKOTAS AND UPPER MIDWEST
16Z UPDATE... VERY MINOR RESHAPING OF THE WESTERN BOUNDARY OF THE
SLIGHT RISK TO REFLECT THE LATEST GUIDANCE TREND AND WPC QPF.
CAMPBELL
CONTINUE TO MAKE MINOR ADJUSTMENTS TO THE PLACEMENT OF A SLIGHT
RISK AREA MAINLY CONFINED TO MINNESOTA AS A SHORTWAVE TROUGH
CONTINUES TO PROPAGATE EASTWARD ALONG THE NORTHERN TIER OF STATES.
THERE HAS BEEN AN UPWARD TREND IN THE GUIDANCE...BOTH IN THE
COARSER/GLOBAL GUIDANCE AND WITH THE CAMS AND RELATED ENSEMBLE
FORECAST SYSTEMS. WITH GUIDANCE NOW SHOWING 2000 TO 3000 J PER KG
BEING POSSIBLE AND PRECIPITABLE WATER VALUES APPROACHING 1.5
INCHES,,,ANOTHER EXPANSION SOUTHWARD OF THE SLIGHT AND MARGINAL
RISK AREAS WAS MADE COMPARED WITH THE PREVIOUS OUTLOOK.
THE MARGINAL RISK AREA ON THE NORTHERN/WESTERN PERIPHERY OF THE
SLIGHT RISK AREA WAS EXPANDED INTO NORTH DAKOTA AS A WELL DEVELOPED
LINE OF CONVECTION WAS MOVING ACROSS THE STATE AND NOT LIKELY TO
DIMINISH PRIOR TO THE START OF THE DAY 1 PERIOD AT 12Z.
..THE OHIO VALLEY AND MID ATLANTIC TO SOUTHERN NEW ENGLAND
16Z UPDATE... THE LATEST GUIDANCE SHOW A LINE OF THUNDERSTORMS
ADVANCING SOUTH/SOUTHEAST THROUGH THE MIDWEST THAT BEGIN TO BOW,
PICK UP PACE, AND TRACK THROUGH WESTERN KENTUCKY. THE RAINFALL
RATES WITH THIS BOWING SEGMENT APPROACHED 1-1.5 INCHES PER HOUR.
AS SUCH, THE MARGINAL RISK AREA WAS EXPANDED SOUTHERN INTO WESTERN
KENTUCKY. GUIDANCE ALSO DEPICTED THAT PORTIONS OF UPSTATE NEW
YORK, SOUTHERN VERMONT AND NEW HAMPSHIRE WOULD SEE AN INCREASE IN
QPF THEREFORE SUGGESTING A NORTH/EAST ADJUSTMENT OF THE MARGINAL
RISK IN THAT REGION.
CAMPBELL
THE SLIGHT RISKS WHICH WERE RAISED OVER THE OHIO VALLEY WAS
EXPANDED TO THE WEST AS A COMPLEX FROM OVERNIGHT MOVES EASTWARD.
THE EXPECTATION IS THAT THE CONVECTION SHOULD WEAKEN FOR A PERIOD
BEFORE REIGNITING LATER. MADE A FEW CHANGES TO THE OUTLOOK AREA
FROM THE DELMARVA NORTHWARD BASED ON LATEST GUIDANCE. LOCALLY
ENHANCED RAINFALL WILL PERSIST IN THE VERY MOIST ENVIRONMENT NEAR
THE WEST- EAST FRONTAL BOUNDARY.
..SOUTHWEST US
DEEPER MOISTURE THAT MADE ITS WAY ACROSS PARTS OF THE GULF AND
INLAND ACROSS MEXICO SHOULD START TO BE DRAWN NORTHWEST INTO PARTS
OF THE SOUTHWEST UNITED STATES...RESULTING IN SCATTERED LATE DAY
AND EVENING CONVECTION ACROSS PARTS OF NEW MEXICO AND A SMALL
PORTION OF ARIZONA.
BANN
DAY 2
VALID 12Z MON JUL 28 2025 - 12Z TUE JUL 29 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE NORTHERN PLAINS...
..PLAINS OF EASTERN MONTANA TO PARTS OF THE UPPER MIDWEST
21Z UPDATE... THE LATEST GUIDANCE NOTED A NORTH AND EASTWARD SHIFT
IN THE QPF AXIS. THE PREVIOUS FORECAST FOCUSED THE HIGHER AMOUNTS
ACROSS EASTERN SOUTH DAKOTA AND NORTHERN IOWA, WHEREAS NOW IT IS
MORE OVER SOUTH/CENTRAL MINNESOTA AND WESTERN WISCONSIN. WITH THIS
TREND THE MARGINAL RISK WAS REDUCED OUT OF WYOMING AND SOUTHWEST
SOUTH DAKOTA, NORTHEAST NEBRASKA AND SOUTHERN IOWA AND THEN
EXPANDED OVER NORTHEAST MONTANA, NORTH DAKOTA, CENTRAL MINNESOTA
AND CENTRAL WISCONSIN. AREAL AVERAGES OF 1 TO 3+ ARE STILL EXPECTED
BUT HOURLY RAINFALL RATES MAY REACH OR EXCEED 1.5 INCHES/HOUR WITH
ANY OF THE EXPECTED STORMS.
CAMPBELL
A SURFACE COLD FRONT AND MID-LEVEL SHORTWAVE TROUGH WILL BE
APPROACHING AN AREA RICH IN MOISTURE AND INSTABILITY OVER PARTS OF
SOUTH DAKOTA AND MINNESOTA/IOWA ON MONDAY AFTERNOON. WITH LOW
LEVEL FLOW LIKELY TO INCREASE THE AMOUNT OF MOISTURE TRANSPORT INTO
THE REGION DURING THE EVENING WITH A CORRESPONDING INCREASE IN
MOISTURE FLUX CONVERGENCE ALONG THE FRONT...THE POTENTIAL EXISTS
FOR EXCESSIVE RAINFALL ESPECIALLY IN THE EVENT OF CELL TRAINING OR
REPEAT CONVECTION. UNCERTAINTY REMAINED WITH RESPECT TO PLACEMENT
IN THE NUMERICAL GUIDANCE...BUT THE RRFS SEEMED TOO FAR NORTH. THE
WPC DETERMINISTIC QPF WAS CLOSER TO A GEFS/ECMWF ENSEMBLE MEAN
POSITION...WHICH STILL LEFT SOME ROOM FOR EXCESSIVE RAINFALL TO
BUILD SOUTH. CONSEQUENTLY...ALLOWED FOR A SOMEWHAT BROADER APRON OF
SLIGHT RISK THAN SHOWN BY GUIDANCE.
SURROUNDING THE SLIGHT RISK AREA...ONLY MODEST CHANGES WERE MADE
TO THE MARGINAL RISK AREA EXTENDING NORTHWEST INTO THE PLAINS OF
EASTERN MONTANA WHERE A SECONDARY QPF MAXIMUM IS EXPECTED. THE
EXPECTATION IS THAT THERE WILL BE TWO DISCRETE QPF AREA WITH A RISK
OF EXCESSIVE RAINFALL ASSOCIATED WITH EACH...BUT MAINTAINED THE
ONE AREA GIVEN THE RANGE OF POSSIBLE SOLUTIONS.
..OHIO/TENNESSEE VALLEYS TO THE CAROLINAS
MUCH OF THE REGION WILL CONTINUE TO HAVE A VERY DEEP COLUMN OF
MOISTURE IN PLACE DURING THIS PERIOD. FLOW IS EXPECTED TO BE SLOW
WHICH WILL BOLSTER THE POTENTIAL FOR STORMS TO BACKBUILD AND GIVEN
THAT SOME LOCATIONS ACROSS THE REGION HAVE STEEP TOPOGRAPHY,
ISOLATED FLASH FLOODING MAY ARISE. SOME OF THE CAMS SHOW RAINFALL
RATES OF 1-1.5+ INCHES/HOUR POSSIBLE. A BROAD MARGINAL RISK WAS
RAISED, SPANNING FROM SOUTHEAST MISSOURI TO THE CAROLINAS.
..SOUTHWEST US
A CONTINUATION OF FLOW WITH DEEPER MOISTURE INTO THE SOUTHWEST US
WILL LINGER ON MONDAY AND MONDAY NIGHT...WITH A CONTINUED CHANCE
FOR SCATTERED LATE DAY AND EVENING CONVECTION ACROSS PARTS OF NEW
MEXICO AND A SMALL PORTION OF ARIZONA THAT EXTENDS NORTHWARD ALONG
THE SOUTHERN AND CENTRAL COLORADO FRONT RANGE.
BANN
DAY 3
VALID 12Z TUE JUL 29 2025 - 12Z WED JUL 30 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE WESTERN HIGH PLAINS...
NORTHERN ROCKIES EASTWARD TO GREAT LAKES AND SOUTHWARD TO THE
SOUTHWEST US...
21Z UPDATE... A PREVIOUSLY NOTED FOR THE D2 PERIOD, THE LATEST QPF
TRENDS CONTINUE TO BE SHIFTED EASTWARD FOR THIS PERIOD AS WELL. THE
AXIS OF CONCENTRATED AMOUNTS WENT FROM NORTHEAST WYOMING TO
NEBRASKA, TO NOW AS FAR EAST AS NORTHERN IOWA. THE SLIGHT RISK WAS
ELONGATED TO NOW INCLUDE MOST OF NORTHERN IOWA. THE MARGINAL RISK
WAS NUDGED A BIT FURTHER NORTH ACROSS WISCONSIN.
CAMPBELL
BUILDING MID-LEVEL RIDGE OVER BRITISH COLUMBIA AND ALBERT WILL
RESULT IN LOWERING HEIGHTS OVER PARTS OF THE NORTHWESTERN US AND
INCREASING MID- AND UPPER FLOW. THIS RESULTS IN AN INCREASINGLY
WELL DEFINED SURFACE BOUNDARY THAT SERVES TO FOCUS SHOWERS AND
THUNDERSTORM ON TUESDAY. INGREDIENTS FOR THUNDERSTORMS TO PRODUCE
HEAVY TO POTENTIALLY EXCESSIVE RAINFALL APPEAR TO BE ALIGNING FROM
SOUTHEAST MONTANA INTO NORTHERN NEBRASKA ALONG A CORRIDOR OF 1000
TO 2000 J PER KG INSTABILITY AND 1 TO 1.25 INCH PRECIPITABLE
WATER VALUES...AND EVEN SOME 1.5 INCH PW VALUES IN NORTHERN
NEBRASKA. SHOWERS AND THUNDERSTORMS ARE ALSO LIKELY TO SPREAD
EASTWARD TOWARD THE GREAT LAKES WHERE THE INSTABILITY AND SYNOPTIC
SCALE FORCING LOOKS TO BE WEAKER. IN ADDITION...ANOTHER ROUND OF
LATE DAY CONVECTION IS POSSIBLE FROM THE SOUTHWEST US INTO THE
ROCKIES AND SOME OF THIS MOISTURE MAY APPROACH...IF NOT COME INTO
PLAY,,,ACROSS THE WESTERN HIGH PLAINS LATE IN THE PERIOD.
..SOUTHEAST US
21Z UPDATE... THE FOOTPRINT ACROSS THE SOUTHEAST INCREASED, LEADING
TO THE WESTWARD EXPANSION OF THE MARGINAL ACROSS SOUTHEAST
LOUISIANA AND NORTHWARD INTO SOUTH CAROLINA AND WESTERN PORTIONS OF
NORTH CAROLINA.
CAMPBELL
PRECIPITABLE WATER VALUES IN EXCESS OF 2 INCHES WILL BE IN PLACE
WITH 1000-1500 J PER KG OF CAPE IN PLACE AND WEAKENING OF THE BROAD
UPPER LEVEL RIDGE SHOULD LEAD TO A SOMEWHAT BETTER CHANCE FOR
SHOWERS OR THUNDERSTORMS ON TUESDAY. THE GFS AND ECMWF BOTH SHOW
HINTS AT WEAK VORTICITY CENTERS IN THE VICINITY TO HELP
FOCUS/SUPPORT SOME ACTIVITY. THE EXPECTATION IS THAT ISOLATED BUT
VERY INTENSE RAINFALL RATES COULD LEAD TO ISOLATED INSTANCES OF
EXCESSIVE RAINFALL.
BANN
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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