575
FOUS30 KWBC 151605
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1205 PM EDT MON SEP 15 2025
DAY 1
VALID 16Z MON SEP 15 2025 - 12Z TUE SEP 16 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
EASTERN NORTH CAROLINA AND SOUTHEASTERN VIRGINIA...
..EASTERN NORTH CAROLINA AND SOUTHEAST VIRGINIA
WV IMAGERY OFF THE NC COAST INDICATES CONVECTION ASSOCIATED WITH A
DEEPENING LOW PRESSURE. THIS FEATURE IS DEEPENING IN RESPONSE TO
POTENT CLOSED LOW (500MB HEIGHTS BELOW THE 10TH PERCENTILE
ACCORDING TO NAEFS) DIGGING ACROSS THE CAROLINAS AND INTERACTING
WITH A STATIONARY FRONT OFFSHORE. SUBTLE UPPER DIFFLUENCE IN THE
DISTANT RRQ OF A JET STREAK NEAR NEW ENGLAND IS ADDITIONALLY
PROVIDING ASCENT, LEADING TO PRESSURE FALLS WITHIN THE SURFACE LOW.
THIS SHOULD CONTINUE TO DEEPEN THE WAVE OFFSHORE, LEADING TO
INTENSIFYING ONSHORE MOIST FLOW (850MB WINDS REACHING -3 SIGMA IN
TO THE WEST) DRIVING INTENSE MOISTURE CONFLUENCE INTO NC/VA THROUGH
TONIGHT AS THE LOW LIFTS VERY SLOWLY NORTH/NORTHWEST, LIKELY
MOVING ONSHORE THE OUTER BANKS BEFORE 12Z TUESDAY.
WHILE THERE CONTINUES TO BE SOME UNCERTAINTY INTO THE EXACT TIMING
AND TRACK OF THIS LOW PRESSURE SYSTEM, GUIDANCE HAS TRENDED
STRONGER WITH MORE PRONOUNCED MOISTURE ADVECTION TO THE W/NW. THIS
WILL RESULT IN HEAVY RAINFALL SPREADING ONSHORE FROM SOUTHEAST
NORTH CAROLINA THROUGH THE TIDEWATER REGION OF VA AND POTENTIALLY
REACHING AS FAR NORTH AS SOUTHERN DELAWARE BEFORE TUESDAY MORNING.
THE HEAVIEST RAINFALL IS LIKELY TO FALL ALONG AN AXIS OF STRONG
900-700MB FGEN ALIGNED JUST NW OF THE SURFACE LOW, WITH ADDITIONAL
HEAVY RAIN LIKELY ANYWHERE NORTH OF THE LOW CENTER DUE TO
PERSISTENT ONSHORE FLOW AND CONVERGENCE. IN THESE AREAS, THIS
ONSHORE FLOW WILL ADDITIONALLY SURGE INSTABILITY TO 250-500 J/KG,
ESPECIALLY THIS EVENING/TONIGHT, WHICH, WHILE MODEST, WILL BE
SUFFICIENT IN THE VERY MOIST ENVIRONMENT TO IMPROVE RAINFALL
EFFICIENCY AND SUPPORT RAINFALL RATES OF 1-2"/HR. WHERE THESE
TRAIN/REPEAT, TOTAL RAINFALL OF 3-5" WITH LOCALLY HIGHER AMOUNTS
ARE LIKELY.
ALTHOUGH THIS AREA HAS BEEN DRY RECENTLY (7-DAY RAINFALL FROM AHPS
GENERALLY LESS THAN 5% WITH FEW EXCEPTIONS) LEADING TO ELEVATED
FFG, THIS TYPE OF RAINFALL CAN STILL OVERWHELM THE SOILS IN
SCATTERED LOCATIONS. THIS IS REFLECTED BY 12Z HREF 3-HR FFG
EXCEEDANCE PROBABILITIES RISING TO AROUND 20%, SO DESPITE THE
ANTECEDENT DRYNESS, AND AFTER COORDINATION WITH WFOS MHX/RAH/AKQ, A
TARGETED SLGT RISK WAS INTRODUCED WITH THIS D1 UPDATE.
..OZARKS
A WEAK MID-LEVEL IMPULSE PUSHING INTO A SHORT-WAVELENGTH BUT HIGH
AMPLITUDE RIDGE THIS EVENING WILL LIKELY RESULT IN SLOW MOVING
SHOWERS AND THUNDERSTORMS. WHILE COVERAGE IS EXPECTED TO BE WIDELY
SCATTERED, RAINFALL RATES WITHIN CONVECTION WILL LIKELY REACH
1-2"/HR IN RESPONSE TO IMPRESSIVE THERMODYNAMICS CHARACTERIZED BY
MUCAPE OF 2000-3000 J/KG OVERLAPPING PWS OF 1.5 TO 1.75 INCHES.
THESE STORMS WILL ADDITIONALLY MOVE QUITE SLOWLY AS 0-6KM MEAN
WINDS WILL BE JUST AROUND 5 KTS, WITH ADDITIONALLY CHAOTIC AND SLOW
PROPAGATION VECTORS. WHILE LOCALLY THIS COULD RESULT IN 2-3" OF
RAIN (HREF AND REFS PROBABILITIES FOR EXCEEDING 3" PEAK AROUND
20-30%), THIS WILL FALL ATOP DRY SOILS LEADING TO ONLY AN ISOLATED
CHANCE OF FFG EXCEEDANCE. OPTED TO HOLD OFF ON A MRGL RISK FOR THIS
AREA AS THE PROBABILITY APPEARS TO BE LESS THAN 5% FOR EXCESSIVE
RAINFALL TODAY.
WEISS
DAY 2
VALID 12Z TUE SEP 16 2025 - 12Z WED SEP 17 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHWEST, THE CENTRAL HIGH PLAINS, AND VIRGINIA/NORTH
CAROLINA...
..SOUTHWEST
SCATTERED CONVECTIVE PATTERN WILL INITIATE ON TUESDAY AFTERNOON AND
EARLY EVENING BEFORE FADING WITH THE LOSS OF DIURNAL HEATING.
CURRENT PROGS ARE FOR CONVECTION TO BE TIED CLOSER TO THE TERRAIN
ACROSS SOUTHEAST AZ INTO SOUTHERN NM WITH ISOLATED SIGNATURES OF
>1"/HR PLAUSIBLE IN THE STRONGER CELL CORES. THESE AREAS GENERALLY
PRONE TO RUNOFF DUE TO TERRAIN COMPLEXITIES, AS WELL AS REMNANT
BURN SCARS PRESENT IN SOME LOCATIONS. MAINTAINED CONTINUITY FROM
INHERITED MRGL RISK WITH SOME MINOR ADJUSTMENTS TO REMOVE EL PASO
PROPER.
..CENTRAL HIGH PLAINS
STRONG SHORTWAVE TROUGH EJECTION OUT OF THE INTERIOR NORTHWEST WILL
LEAD TO CONVECTIVE DEVELOPMENT AND REGIONAL ENHANCEMENT ACROSS THE
CENTRAL HIGH PLAINS. GREATEST ASCENT IS ALIGNED WITH THE DIFFLUENT
REGION OF THE MID-LEVEL SHORTWAVE WITH LEFT-EXIT REGION DYNAMICS
LIKELY TO MAINTAIN A PREVALENT HEAVY RAIN SIGNATURE ACROSS THE
WESTERN THIRD OF NE DOWN INTO NEIGHBORING NORTHEAST CO AND
NORTHWEST KS. HEAVIEST RAIN COULD REMAIN JUST OUTSIDE OF THE RISK
AREA ACCORDING TO SOME GUIDANCE LEADING TO LOW PROBABILITY OF FLASH
FLOODING DUE TO THE OCCURRENCE WITHIN THE WESTERN SAND HILLS.
THERE'S STILL A GOOD AGREEMENT ON LOCALIZED MAXIMA WITHIN THE HI-
RES ENSEMBLE MEANS, PIN-POINTING THE AREA WEST OF NORTH PLATTE, NE
AS ONE OF THE FAVORABLE SPOTS FOR CONVECTIVE IMPACTS. FFG'S IN THIS
CORRIDOR ARE LOWER THAN THE NEIGHBORING SAND HILL DOMAIN, SO THE
MRGL RISK REMAINS RELATIVELY SMALL.
..VIRGINIA AND NORTH CAROLINA
OUR SURFACE LOW WILL MATURE AND OCCLUDE BY TUESDAY AFTERNOON AS THE
CLOSED HEIGHT FIELDS INDICATE THE 850/700/500 MB LOWS BECOMING
VERTICALLY STACKED LEADING TO A SLOW DECAY OF THE SURFACE LOW BY
THE SECOND HALF OF THE PERIOD. PERSISTENT HEAVY RAIN POTENTIAL WILL
LINGER ACROSS EASTERN NC UP INTO THE VA TIDEWATER LEADING TO
MULTI-DAY TOTALS REACHING 2-4" WITH LOCALLY UPWARDS OF 6-7" OVER
THE SPAN OF 48 HRS. DESPITE THE DRIER SOILS LEADING INTO THE EVENT,
THE CUMULATIVE EFFECT WILL LEAD TO AREAL FLOODING CONCERNS FOR
PORTIONS OF THE ABOVE LOCATIONS. SOME WESTERLY PUSH OF THE HEAVIER
QPF IS PROGGED IN THE FRONT HALF OF D2 LEADING TO SOME AREAS IN
NORTH-CENTRAL NC UP THROUGH SOUTH-CENTRAL VA POSSIBLY SNEAKING INTO
THE FLASH FLOOD THREAT. THE ONLY GOOD NEWS IS THE WEAKENING SURFACE
LOW WILL LEAD TO DEGRADING RATES EVENTUALLY, AND SLOW WANE ON THE
THREAT. THE MRGL RISK INHERITED WAS MAINTAINED WITH SOME MINOR
WESTERLY EXPANSIONS TO ACCOUNT FOR RECENT TRENDS IN THE ENSEMBLE
MEANS.
KLEEBAUER
DAY 3
VALID 12Z WED SEP 17 2025 - 12Z THU SEP 18 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PARTS OF THE
NORTHERN AND CENTRAL PLAINS, SOUTHERN HIGH PLAINS, AND SOUTHEAST
FLORIDA...
..NORTHERN AND CENTRAL PLAINS
A STRONG MID-LEVEL SHORTWAVE TROUGH WILL EJECT INTO THE WY FRONT
RANGE AND EVENTUALLY CLOSE OFF ACROSS NE GENERATING A MATURING LEE
CYCLONE ACROSS THE CENTRAL HIGH PLAINS. THE SETUP WILL LIKELY CAUSE
QUITE A ROBUST DEFORMATION SIGNATURE ON THE NORTHWEST FLANK OF THE
CYCLONE WITH ENSEMBLE MEAN QPF PLACEMENT SITUATED OVER WESTERN NE
UP THROUGH SOUTHWESTERN SD, ARCING BACK INTO THE NOSE OF THE WARM-
CONVEYOR BELT ON THE NORTHEAST SIDE OF THE SYSTEM. THIS IS A
CLASSIC MID-LATITUDE LEE CYCLOGENESIS SETUP WITH A STRONG JET
COUPLING LEADING TO BROAD LARGE SCALE FORCING AND WIDESPREAD PRECIP
ACROSS THE PLAINS. EASTERN SIDE OF THE CYCLONE WILL EXHIBIT THE
BEST CONVECTIVE POTENTIAL WHILE THE DEFORMATION AXIS PROVIDES A
SOLID PRECIP FIELD WITH MODERATE TO LOCALLY HEAVY RATES FOR SEVERAL
HRS. IN THAT NORTHWEST SIDE OF THE LOW. TOTALS >2" ARE FORECAST
WITHIN THE MEANS ACROSS WESTERN NE INTO SD WITH SCATTERED ELEVATED
QPF ACROSS THE MISSOURI RIVER BASIN LOCATED IN EASTERN SD AND NE.
THIS SETUP IS CONDUCIVE FOR AT LEAST SOME ISOLATED TO SCATTERED
FLASH FLOOD PROSPECTS CONSIDERING THE SYNOPTIC EVOLUTION. THIS WAS
ENOUGH TO WARRANT A MRGL RISK IN THOSE AREAS DEEMED THE BEST CHANCE
FOR HEAVY RAIN PROSPECTS.
..SOUTHERN HIGH PLAINS
MATURING LEE SIDE LOW TO THE NORTH WILL HELP DRAG A TRAILING COLD
FRONT THROUGH THE CENTRAL AND SOUTHERN HIGH PLAINS ON WEDNESDAY.
THE FRONT WILL SLIP SOUTH AND SOUTHWEST ONCE DOWN NEAR THE
LATITUDE OF THE OK PANHANDLE, LEADING TO A MORE TEXTBOOK BACKDOOR
FRONTAL PROGRESSION AS IT ENTERS INTO THE NORTHERN TX PANHANDLE AND
NORTHEAST NM. FLOW BEGINS TO RUN MORE PARALLEL TO THE BOUNDARY IN
THESE ZONES WHEN ASSESSING FORECAST SOUNDINGS FROM RELEVANT GLOBAL
DETERMINISTIC. THE KEY IN THE SETUP IS A RELATIVELY SOLID
ISENTROPIC ASCENT PATTERN IN A SMALL ZONE BORDERING CO/OK/NM/TX
WITH CROSS-SECTION VIEWS OVER THE AREA DISPLAYING A CLASSIC SLOPED
LOW-LEVEL SURFACE FGEN WITH STRONG OMEGA CORRELATING TO RAPID
ASCENT AS THE FRONT PROGRESSES THROUGH THE AREA. LOCALLY ENHANCED
CORRIDOR OF PRECIP WILL TRANSPIRE ALONG AND IN WAKE OF THE FRONT
WITH LOCAL MAXIMA OF 1.5" TO AS MUCH AS 3" PLAUSIBLE DURING THE
EVENT. THIS COULD BE ENOUGH FOR AN ISOLATED FLASH FLOOD THREAT,
ESPECIALLY IN THOSE SMALLER URBAN AREAS SITUATED ACROSS THE 4 STATE
INTERSECTION. A MRGL RISK HAS BEEN ADDED TO ACCOUNT FOR THE THREAT.
..SOUTHEAST FLORIDA
STALLED FRONT WITH AN ENHANCED MOISTURE RETURN ACROSS SOUTH FL WILL
LEAD TO A HEIGHTENED THREAT FOR FLASH FLOODING OVER THE URBAN
CENTERS OF SOUTHEAST FL. DETERMINISTIC OUTPUT IS SCATTERED IN THE
EXACT LOCATION OF THE HEAVIEST PRECIP, RANGING FROM THE KEYS UP TO
WEST PALM BEACH AND EVERYWHERE IN-BETWEEN. THE SETUP IS
HISTORICALLY FAVORABLE FOR FLASH FLOOD CONCERNS OVER THE URBAN
ZONES OF SOUTHEAST FL WITH PWATS HOVERING BETWEEN 2-2.3", A SOLID
1/1.5 DEVIATIONS ABOVE NORMAL. IN COORDINATION WITH THE MIAMI WFO,
A MRGL WAS MAINTAINED FOR THAT URBANIZED COASTAL CORRIDOR BETWEEN
WEST PALM DOWN TO MIAMI PROPER SINCE THIS IS THE MOST LIKELY
LOCATION FOR FLASH FLOODING IN THIS TYPE OF SETUP. WILL MONITOR
CONVECTIVE TRENDS AS WE GET CLOSER TO SEE IF THIS NECESSITATES ANY
EXPANSION, OR EVEN A TARGETED UPGRADE.
KLEEBAUER
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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