981
FOUS30 KWBC 290045
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
845 PM EDT MON JUL 28 2025
DAY 1
VALID 01Z TUE JUL 29 2025 - 12Z TUE JUL 29 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE NORTHERN PLAINS AND UPPER MISSISSIPPI VALLEY..
..NORTHERN PLAINS TO UPPER MS VALLEY
CONVECTION IS IN THE PROCESS OF GROWING UPSCALE INTO AN MCS AS IT
MOVES ACROSS CENTRAL SD INTO SOUTHERN MN AND NORTHERN IA THIS
EVENING. A FORWARD PROPAGATING MCS (LIKELY TO BECOME A DERECHO)
WILL CONSOLIDATE AND MOVE EASTWARD, WHERE A SLIGHT RISK WAS
MAINTAINED. VERY IMPRESSIVE INSTABILITY (SBCAPE OF 4000-7500 J/KG)
AND TROPOSPHERIC MOISTURE (PWS AROUND 2", NEAR THE DAILY MAX PER
OAX SOUNDING CLIMATOLOGY) DOWNSTREAM OF THE MCS WILL SUPPORT VERY
EFFICIENT, HEAVY RAINFALL RATES WITH HOURLY ACCUMULATIONS UP TO
2-3" LOCALLY. AS THE MCS MATURES (HIGHLY LIKELY, GIVEN 30-50 KTS OF
DEEP LAYER SHEAR AND DERECHO COMPOSITE PARAMETER OF 6-8) THE
HEAVIEST RAINFALL TOTALS WILL LIKELY END UP NEAR THE DEVELOPING
COMMA HEAD/BOOKEND VORTEX WHERE HEAVY RAINFALL DURATION WILL BE
LOCALLY LONGER. THE 18Z HREF SUGGESTS THE POTENTIAL FOR ADDITIONAL
TOTALS (12-HR TOTALS THROUGH 12Z) IN EXCESS OF 5" (PER 40-KM
NEIGHBORHOOD PROBS OF ~10%) WITH A NARROW AXIS OF OVER 3" POSSIBLE
AS WELL (30-50%). THE PORTION OF WEST-CENTRAL MN INTO SOUTH-CENTRAL
MN WHERE THIS OUTCOME IS MOST LIKELY IS FAIRLY RURAL AND JUDGED TO
BE A HIGHER-END SLIGHT RISK FROM A PROBABILITY PERSPECTIVE (AS
6-HR FFGS SUGGEST SOME OF THE MORE VULNERABLE TERRAIN ACROSS THIS
AREA WITH VALUES GENERALLY NEAR 2.0").
..SOUTHWEST
AT LEAST AN ISOLATED FLASH FLOOD THREAT WILL CONTINUE INTO THE
EARLY EVENING HOURS WITH IMPRESSIVE CONVECTIVE COVERAGE ONGOING
OVER SOUTHERN NM AND INTO SOME SURROUNDING PORTIONS OF CENTRAL NM,
WEST TX, AND FAR SOUTHWEST AZ. CONVECTIVE COVERAGE SHOULD GRADUALLY
WANE INTO THE NIGHT WITH THE LOSS OF DAYTIME HEATING AND
INCREASING CIN, BUT IN THE MEANTIME HIGHLY ANOMALOUS MOISTURE (PER
PWS OF 1.25"+ BEING THE 90TH PERCENTILE OR HIGHER LOCALLY) WILL
SUPPORT EFFICIENT DOWNPOURS AND A RESULTING FLASH FLOOD THREAT
(PARTICULARLY FOR BURN SCARS).
..OH VALLEY INTO THE CAROLINAS
ISOLATED TO SCATTERED THUNDERSTORMS TO CONTINUE THIS EVENING ACROSS
A BROAD AREA STRETCHING FROM KY/IN/OH TO THE COASTAL CAROLINAS.
WHILE OVERALL CONVECTIVE ORGANIZATION IS LIMITED WITH DECLINING
COVERAGE AND INTENSITY INTO THE LATE OVERNIGHT HOURS, PWS OF
AROUND 2" (OR HIGHER) WILL CONTINUE TO SUPPORT HEAVY RAINFALL
RATES (LOCALLY AS HIGH AS 1-3"/HR) WITHIN A BROAD MARGINAL RISK
AREA. THE MOST CONCENTRATED FLASH FLOOD THREAT IN THE NEAR TERM
EXISTS ACROSS EASTERN OH AND SURROUNDING (SEE MPD #820 FOR MORE
INFORMATION).
CHURCHILL
DAY 2
VALID 12Z TUE JUL 29 2025 - 12Z WED JUL 30 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL AND NORTHERN PLAINS AND FOR PORTIONS OF THE SOUTHWEST...
..CENTRAL AND NORTHERN PLAINS
21Z UPDATE... THE TREND OF SHIFTING THE QPF FOOTPRINT FURTHER EAST
ACROSS THE CENTRAL U.S. PERSISTED WITH THE MOST RECENT RUN OF
GUIDANCE. PORTIONS OF SOUTHERN IOWA, NORTHWEST MISSOURI AND
NORTHERN KANSAS SAW AN UPTICK IN COVERAGE AND AMOUNTS FOR THIS
PERIOD. AS SUCH THE SLIGHT RISK AREA WAS EXPANDED ON ITS EASTERN
BOUNDARY TO COVER THIS PART OF THE REGION. HOURLY RAIN RATES OF
1-2 INCHES/HOUR STILL EXPECTED TO PASS THROUGH THE PLAINS TOWARD
THE MIDWEST.
CAMPBELL
A STATIONARY FRONT WILL LIKELY EXTEND ACROSS SOUTHERN IA/NE AND
INTO THE HIGH PLAINS ON TUESDAY AFTERNOON/EVENING. EASTERLY FLOW TO
THE NORTH OF THIS FRONT WILL LIKELY HELP TRIGGER CONVECTIVE
DEVELOPMENT OVER THE HIGH PLAINS AS SHORTWAVE ENERGY MOVES OUT OF
THE ROCKIES AND UPPER LEVEL DIVERGENCE INCREASES IN THE RIGHT
ENTRANCE REGION OF AN UPPER JET. THIS ACTIVITY WILL LIKELY PUSH
EAST INTO THE OVERNIGHT HOURS ACROSS NE AND EVENTUALLY IA
ALONG/NORTH OF THE STATIONARY FRONT. UPSCALE DEVELOPMENT INTO AN
MCS APPEARS PROBABLE DRIVING A HEAVY RAINFALL THREAT. ANY EVENTUAL
MCS WILL PROBABLY PROPAGATE OFF TO THE EAST FAIRLY QUICKLY, HOWEVER
ADDITIONAL DEVELOPMENT DOWNSTREAM OVER NE/IA IS POSSIBLE GIVEN THE
CONVERGENCE NEAR THE FRONT AND WHAT SHOULD BE CAPE AROUND 4000
J/KG. PWS SHOULD BE PLENTY HIGH ENOUGH FOR HEAVY RAINFALL, RANGING
FROM 1.5" IN THE HIGH PLAINS TO LOCALLY OVER 2" FROM EASTERN NE
INTO IA.
THERE REMAINS SOME LATITUDINAL UNCERTAINTY WITH THE AXIS OF
CONVECTION DURING THIS PERIOD...ALTHOUGH THE GENERAL TREND HAS
BEEN FOR A SLIGHTLY FARTHER SOUTH AXIS. THERE IS ALSO SOME QUESTION
AS TO HOW FAR EAST THE RISK EXISTS, WITH THE DETERMINISTIC AND
ENSEMBLE EC AND THE 00Z RRFS/REFS FAVORING NE, BUT THE GFS AND
AIFS EXTENDING THE THREAT INTO IA. GIVEN A FAVORABLE TRACK RECORD
FOR THE AIFS AND THE PRESENCE OF THE BOUNDARY/INSTABILITY/PWS OVER
IA, WE DID WANT TO MAKE SURE THAT THE SLIGHT RISK AT LEAST COVERED
INTO CENTRAL IA.
..SOUTHWEST
21Z UPDATE... THE SIGNAL FOR HEAVY RAINFALL INCREASED FOR PORTIONS
OF NEW MEXICO AND FAR SOUTHWEST ARIZONA FOR THIS PERIOD. MUCH OF
THIS PART OF THE REGION IS SENSITIVE TO HIGHER RAINFALL
INTENSITIES/AMOUNTS. IN COORDINATION WITH THE LOCAL FORECAST
OFFICES CONCERN WAS RAISED FOR NOT ONLY RECENT BURN SCARS BUT ALSO
THE SANGRE DE CRISTO MOUNTAINS AND POSSIBLY THE GILA REGION OF
SOUTHWEST NM. A SLIGHT RISK WAS RAISED FOR THIS PERIOD TO COVER
THIS INCREASED THREAT FOR LOCAL FLASH FLOODING POTENTIAL.
CAMPBELL
ANOTHER DAY OF SCATTERED AFTERNOON CONVECTION EXPECTED TUESDAY.
PROBABILITIES FROM BOTH THE 00Z HREF AND REFS SHOW A BIT MORE
PERSISTENCE OF HIGH 1"/HR EXCEEDANCE OVER THE SACRAMENTO MOUNTAINS
AND VICINITY. THUS THE FLASH FLOOD RISK OVER THESE AREAS, AND THE
SUSCEPTIBLE BURN SCARS, MAY VERY WELL BE HIGHER TUESDAY THAN
MONDAY. HOWEVER THERE ARE SOME QUESTIONS REGARDING THE COVERAGE OF
HEAVIER RAINFALL AMOUNTS AWAY FROM THESE TERRAIN AREAS, AS THE
OVERALL COVERAGE COULD BE A BIT LESS THAN MONDAY. GIVEN THE SMALL
EXTENT OF THE HIGHER RISK AT THE MOMENT AND THE UNCERTAINTY ON THE
BROADER COVERAGE, WE WILL LEAVE THE ERO AT A MARGINAL LEVEL PENDING
WHAT HAPPENS MONDAY. ALTHOUGH LOCALLY SIGNIFICANT IMPACTS ARE
POSSIBLE WITHIN/NEAR THE SACRAMENTO MOUNTAIN BURN SCARS.
..SOUTHEAST
EXPECTING GREATER CONVECTIVE COVERAGE ON TUESDAY FROM THE SOUTHEAST
INTO THE SOUTHERN APPALACHIANS. NOT MUCH IN THE WAY OF FORCING TO
ORGANIZE CONVECTION, AND GENERALLY EXPECTING PULSE ACTIVITY THAT
DOES NOT LAST ALL THAT LONG AT ANY ONE LOCATION. THIS WILL ACT AS
A LIMITING FACTOR FOR FLASH FLOODING...HOWEVER THERE SHOULD BE
ENOUGH CONVECTIVE COVERAGE THAT SOME CELL MERGERS ALONG OUTFLOWS
WILL BE A POSSIBILITY. PWS IN THE REGION ARE FORECAST BETWEEN 2"
AND 2.3", WITH CAPE OVER 2000 J/KG...SO THE THERMODYNAMIC
ENVIRONMENT WILL SUPPORT HEAVY RAINFALL RATES. THUS EVEN WITH A
RELATIVELY SHORT DURATION OF RAIN AT ANY ONE LOCATION, RAINFALL
TOTALS LOCALLY OVER 3" APPEAR PROBABLE DRIVING A LOCALIZED FLASH
FLOOD RISK.
CHENARD
DAY 3
VALID 12Z WED JUL 30 2025 - 12Z THU JUL 31 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE MIDDLE MISSISSIPPI VALLEY AND FOR PORTIONS OF THE FRONT RANGE
AND ADJACENT HIGH PLAINS...
..MID MS VALLEY
21Z UPDATE... THE AREA HIGHLIGHTED FOR THE SLIGHT RISK AREA REMAINS
IN GOOD ORDER, ONLY MINOR RESHAPING OF THE BOUNDARY MADE TO REFLECT
THE LATEST WPC QPF AND MODEL TRENDS.
CAMPBELL
AT 12Z WEDNESDAY IT SEEMS LIKELY THAT WE WILL HAVE SOME DEGREE OF
ORGANIZED CONVECTION ONGOING IN THE VICINITY OF IA, ALTHOUGH AT
THIS LEAD TIME GETTING THESE SPECIFICS RIGHT IS TRICKY.
NONETHELESS, IT APPEARS PROBABLE THAT A BETTER DEFINED
SHORTWAVE/MCV WILL BE ASSOCIATED WITH THIS CONVECTION AND SLOWLY
MOVE EAST ACROSS IA/MO/IL AND VICINITY WEDNESDAY INTO WEDNESDAY
NIGHT. MEANWHILE WE WILL HAVE A SLOWLY SOUTHWARD SHIFTING COLD
FRONT HELPING FOCUS CONVERGENCE, AND THE RIGHT ENTRANCE REGION OF
THE UPPER JET ADDING SOME DIVERGENCE ALOFT. WITH PLENTIFUL CAPE
NEAR THE FRONT AND PWS LOCALLY OVER 2", THE INGREDIENTS FOR AREAS
OF EXCESSIVE RAINFALL ARE IN PLACE. SOME UNCERTAINTY REMAINS ON THE
DETAILS...BUT 00Z MODELS ARE COMING INTO A BETTER CONSENSUS ON THE
FAVORED AXIS FOR HEAVY RAINFALL..GENERALLY STRETCHING ACROSS
PORTIONS OF IA, NORTHERN MO AND INTO CENTRAL/NORTHERN IL AND
POSSIBLY PORTIONS OF IN.
..SOUTHWEST AND HIGH PLAINS
21Z UPDATE... THERE IS A GROWING SIGNAL FOR CONVECTION TO FIRE UP
ALONG THE FRONT RANGE AND THE ADJACENT HIGH PLAINS. THE NATURE OF
COVERAGE STILL SEEMS TO BE SCATTERED HOWEVER GUIDANCE HAS
CONSENSUS OF 1 TO 2 INCHES FOR AREAL MAXIMUMS WITH ISOLATED
LOCATIONS POTENTIALLY REACHING 3 INCHES OR HIGHER. IN COORDINATION
WITH THE LOCAL FORECAST OFFICES, OPTED TO RAISE A SLIGHT RISK FOR
EASTERN COLORADO, SOUTHEAST WYOMING, WESTERN KANSAS, SMALL PORTIONS
OF THE OKLAHOMA AND TEXAS PANHANDLES, AND NORTHEAST NEW MEXICO.
CAMPBELL
ISOLATED TO SCATTERED CONVECTION WILL LIKELY DEVELOP NEAR AREAS OF
TERRAIN FROM NM INTO THE ROCKIES. GENERALLY NOT LOOKING LIKE THE
GREATEST FORCING, SO THE DEGREE OF CONVECTIVE ORGANIZATION REMAINS
UNCLEAR. AT THE MOMENT MOST MODELS INDICATE MOSTLY
ISOLATED/SCATTERED DEVELOPMENT, AND GENERALLY NOT ENOUGH COVERAGE
FOR ANYTHING MORE THAN A MARGINAL RISK. HOWEVER THERE IS SOME
POTENTIAL FOR A FEW ORGANIZED CLUSTERS TO MOVE OFF THE TERRAIN
INTO THE HIGH PLAINS, AND SO CAN NOT RULE A TARGETED SLIGHT RISK OR
TWO AS WE GET CLOSER IN TIME AND HAVE MORE HIGH RES GUIDANCE TO
INTERROGATE.
..ELSEWHERE
A BROAD MARGINAL RISK EXTENDS FROM THE CENTRAL GULF COAST ALL THE
WAY INTO PORTIONS OF NEW ENGLAND. HIGH PWS AND CAPE AND CONVECTIVE
COVERAGE WILL DRIVE THE RISK FROM THE GULF COAST INTO THE TN
VALLEY. A LACK OF ORGANIZATION MAY KEEP FFG EXCEEDANCE COVERAGE
DOWN, BUT HIGH RAINFALL RATES WILL LIKELY LOCALLY APPROACH OR
EXCEED FFG. A COLD FRONT WILL DRIVE THE RISK FORM PORTIONS OF THE
OH VALLEY INTO NEW ENGLAND. GENERALLY QUICK CELL MOTIONS AND THE
LACK OF A SIGNIFICANT QPF FOOTPRINT IN THE 00Z MODELS KEEP THIS
RISK AT A MARGINAL LEVEL.
CHENARD
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page