844
FOUS30 KWBC 180759
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
359 AM EDT TUE AUG 18 2026
DAY 1
VALID 12Z TUE AUG 18 2026 - 12Z WED AUG 19 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE MIDWEST AND MISSOURI VALLEY...
..MIDWEST TO MISSOURI VALLEY
CURRENT WV SATELLITE IMAGERY DEPICTS THE ARRIVAL OF OUR FIRST
SHORTWAVE MIGRATING SOUTHEAST AROUND THE BROAD TROUGH TO THE NORTH
AND OVER THE NORTHERN FRINGES OF THE RIDGE DOMINATING THE SOUTHERN
CONUS. PATHWAY OF LEAST RESISTANCE WILL MAINTAIN A CONSISTENT
APPROACH OF NORTHWEST TO SOUTHEAST TRAJECTORY OF THE NEXT SERIES OF
SHORTWAVES WANDERING THROUGH THE MEAN FLOW BETWEEN THE TWO KEY
UPPER FEATURES OVER THE NEXT 72 HRS. THE FIRST DISTURBANCE WILL BE
THE PRECURSOR TO A MORE POTENT SHORTWAVE EJECTING OUT OF THE
NORTHERN ROCKIES THE SECOND HALF OF THE PERIOD. ANTICIPATING THE
CURRENT SHORTWAVE ANALYZED OVER THE WYOMING FRONT RANGE THROUGH THE
SANDHILLS TO PROPAGATE EAST-SOUTHEAST WITH THE MAIN ENERGY PIVOTING
THROUGH THE CORN BELT AND UPPER MISSISSIPPI VALLEY BEFORE KICKING
EAST TOWARDS THE SOUTHERN PORTION OF THE GREAT LAKES BY LATER THIS
EVENING AND CONTINUING ITS PROGRESSION EASTWARD. THIS DISTURBANCE
WILL BE THE HEADLINE FEATURE FOR AREAS OF THE MIDWEST BETWEEN
MN/WI/IL WITH THE LATEST CAMS MAINTAINING SOME VARIABILITY IN HOW
THEY WANT TO HANDLE THE CONVECTIVE SCHEME DURING THE AFTERNOON AND
EVENING PERIOD TODAY. CURRENT PROSPECTS ARE GENERALLY 50/50 ON
WHETHER OR NOT WE SEE ANY SIGNIFICANT THUNDERSTORM GENESIS ACROSS
THE AFOREMENTIONED AREA AS RELEVANT POSITIVE VORTICITY ADVECTION
AND THE INTRODUCTION OF A COLD FRONT SHOULD MANIFEST AT LEAST SOME
SCATTERED CONVECTIVE ACTIVITY ACROSS THE UPPER MIDWEST TOWARDS THE
WESTERN GREAT LAKE AREAS SPANNING I-94/41 BETWEEN CHICAGO AND
MILWAUKEE.
DETERMINISTIC OUTPUTS AROUND THE GREAT LAKES MAINTAIN AT LEAST
SOME MODERATE TOTALS WITH A FEW MORE AGGRESSIVE CAMS NOTING MORE
SUBSTANTIAL RAINFALL PROSPECTS AS THE SETUP YIELDS A BETTER
ORGANIZED CONVECTIVE CLUSTER, THUS TIPPING THE SCALES TO A MORE
ENHANCED RAINFALL PROSPECT BY THE LATE-AFTERNOON AND EARLY EVENING
TIME FRAME PRIOR TO THE ARRIVAL OF THE COLD FRONT FROM THE
NORTHWEST. LATEST 00Z HREF NEIGHBORHOOD PROBS FOR >2" IS HOVERING
BETWEEN 20-35% ACROSS NORTHEASTERN IL INTO SOUTHERN WI WITH THE
PRIMARY FOCUS LYING BETWEEN I-94 AND I-80 IN THE ABOVE REGION.
CONSIDERING THE ANTECEDENT SOIL MOISTURE ANOMALIES REMAINING
ELEVATED, ESPECIALLY THE TOP LAYER SOILS WHICH HAVE TAKEN A BEATING
THE PAST WEEK FROM INCESSANT CONVECTIVE COMPLEXES AND THE LIKE, AS
WELL AS ELEVATED STREAM FLOWS LINGERING FROM SAID IMPACTS, THE
PROSPECT FOR LOCALIZED FLASH FLOODING IS A BIT HIGHER THAN NORMAL.
AS SUCH, WITH A SIGNAL STILL PRESENT IN SOME OF THE CAMS AND THE
LOCAL CHICAGO WFO MESSAGING THE THREAT FOR LOCALLY ENHANCED FLOOD
CONCERNS WITH THE DISTURBANCE, THERE WAS NO REASON TO DEVIATE FROM
THE PREVIOUS SLGT RISK IN PLACE AS THE ENVIRONMENTAL CONDITIONS AND
SYNOPTIC PATTERN DO FAVORABLE THE POTENTIAL FOR LATER TODAY BEFORE
THE COLD FRONT FINALLY USHERS IN SOME MUCH NEEDED DRIER AIR IN ITS
WAKE.
FURTHER TO THE WEST AND SOUTHWEST, THE THREAT IS A BIT LESS
VARIABLE IN ITS PRESENTATION WITHIN THE LATEST CAMS SUITE AS THE
SECOND, MORE PROLIFIC SHORTWAVE TO EJECT OUT OF THE NORTHERN
ROCKIES IS ALL BUT CERTAIN TO PROVIDE TO A MORE ENHANCED CONVECTIVE
EPISODE ACROSS AREAS OF EASTERN NE DOWN THROUGH THE QUAD-STATE AREA
OF NE/MO/KS/IA AS THE SHORTWAVE AMPLIFIES AND DIGS SOUTHEAST OUT OF
THE SANDHILLS. FAIRLY TEXTBOOK SETUP OF REGIONAL DIFFLUENCE AHEAD
OF THE TROUGH AS IT MIGRATES THROUGH THE HIGH PLAINS INTO THE
MISSOURI RIVER VALLEY, ENTERING AN ENVIRONMENT THAT WILL YIELD MUCH
MORE FAVORABLE LOW TO MID-LEVEL SHEAR AND ELEVATED PWAT ANOMALIES
AS FLOW BECOMES BACKED FOR A TIME WITH THE TROUGHS APPROACH.
CONVECTIVE INITIATION ACROSS NE WILL ENSUE LATE THIS AFTERNOON,
CARRYING THROUGH THE EVENING AS THE MEAN FLOW WILL TAKE ANY
ACTIVITY AND PRESS IT SOUTHEAST WITH SIGHTS ON NORTHEASTERN KS AND
NORTHERN MO AS WE MOVE INTO THE EVENING. FROM THERE, A MODEST
NOCTURNAL LLJ WILL NOSE UP THROUGH KS ALLOWING FOR A LOCALIZED
CONVERGENCE SIGNATURE AND A NARROW CORRIDOR OF LOW-LEVEL SHEAR
ENHANCEMENT TO MAINTAIN BETTER MESOCYCLONE STRUCTURES THAT WILL
WANDER SOUTHEAST THROUGH NORTHEAST KS INTO MO. HEAVY RAINFALL WILL
MAINTAIN A SOUTHEASTWARD HEADING WITH A PRETTY SOLID CONSENSUS OF
1-2", LOCALLY HIGHER AMOUNTS OF RAINFALL EXTENDING FROM THE KS/NE
BORDER DOWN THROUGH CENTRAL MO. THIS IS HIGHLIGHTED BY MODEST >2"
PROBS OFF THE LATEST HREF WITH THE AXIS ALIGNED PERFECTLY WITH THE
EXPECTED FRONTAL POSITIONING BY THE END OF THE FORECAST. THESE ARE
THE MORE LIKELY LOCATIONS TO SEE FLASH FLOODING GIVEN THE MORE
FAVORABLE FORCING, MOISTURE PRESENCE, AND POTENTIAL FOR REPEATING
LEADING TO A MAINTENANCE OF THE SLGT RISK FROM THE PREVIOUS
FORECAST(S).
KLEEBAUER
..EASTERN FLORIDA PENINSULA
BROAD TROUGH EXPANDING ACROSS THE EAST WILL DIG SLIGHTLY INTO THE
SOUTHEAST TUESDAY, PUSHING A COLD FRONT AND PRE-FRONTAL TROUGH
TOWARDS THE GULF COAST. THIS PRE-FRONTAL TROUGH IS PROGGED TO PUSH
DOWN THE FLORIDA PENINSULA IN RESPONSE TO A PUSH OF A MODEST
SHORTWAVE IMPULSE EMBEDDED WITHIN THE FLOW. AS THIS
TROUGH/SHORTWAVE DIVE SOUTHWARD, THE OVERLAPPING ASCENT WILL MERGE
WITH THE PINNED SEA BREEZE INTO ROBUST THERMODYNAMICS CHARACTERIZED
BY PWS OF 2-2.25 INCHES AND MUCAPE ABOVE 3000 J/KG. THIS WILL
SUPPORT SCATTERED TO WIDESPREAD THUNDERSTORM DEVELOPMENT, WITH
RAINFALL RATES ECLIPSING 2"/HR. WHILE THIS SETUP IS FAVORABLE FOR
LOCALLY ENHANCED RAINFALL AND TOTALS BETWEEN 3-5" IN THE HARDEST
HIT LOCATIONS, ANTECEDENT SOIL MOISTURE REMAINS LOW AND PROBS FOR
FFG EXCEEDANCE MAINTAIN A MEAGER SIGNAL AS FFG'S REMAIN UPWARDS OF
3.5-4"/HR ACROSS ALL OF NORTHEASTERN FL INTO THE FL PANHANDLE.
CONSIDERING THE NATURE OF THE PRECIP BEING SCATTERED IN NATURE AND
THE SIGNALS WITHIN THE LATEST CAMS A LITTLE LESS ROBUST THAN THE
PREVIOUS FORECAST, DECIDED TO REMOVE THE PREVIOUS MRGL RISK, BUT
MAINTAIN A POSTURE FOR A NON-ZERO FLASH FLOOD THREAT WITH THE
GREATEST POTENTIAL LIKELY BETWEEN JACKSONVILLE TO DAYTONA BEACH.
KLEEBAUER/WEISS
DAY 2
VALID 12Z WED AUG 19 2026 - 12Z THU AUG 20 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE MID-MISSISSIPPI AND OHIO VALLEYS...
..MID-MISSISSIPPI AND OHIO VALLEY
AMPLIFYING SHORTWAVE TROUGH FROM THE PREVIOUS PERIOD WILL CONTINUE
ITS PROGRESSION SOUTHEASTWARD WITH SIGHTS ON THE MID-MISSISSIPPI
AND WESTERN OHIO VALLEY'S AS WE STEP THROUGH WEDNESDAY. ENOUGH
TRAILING ENERGY WILL FEED INTO THE BACKSIDE OF THE TROUGH ALLOWING
FOR A BIT MORE OF A ROBUST RESPONSE COMPARED TO WHAT TRANSPIRES
UPSTREAM THE PRIOR EVENING. FIRST ROUND OF CONVECTION WILL THE
REMNANTS OF THE OVERNIGHT MCS WITH EXPECTED DECAY OF THE COMPLEX OF
THUNDERSTORMS AS WE STEP THROUGH WEDNESDAY MORNING. COLD FRONT WILL
ALSO CONTINUE ITS PROGRESSION SOUTH AND SOUTHEASTWARD THROUGH THE
OHIO AND MISSOURI VALLEY DURING THE PERIOD WITH A BIT MORE
LATITUDINAL LOSS FURTHER WEST COMPARED TO DOWNSTREAM. BY WEDNESDAY
AFTERNOON, WE'LL SEE THE INTRODUCTION OF THE SHORTWAVE INTO THE
CENTER OF THE CONUS LEAD TO BROADER AMPLIFICATION OF THE LONGWAVE
TROUGH POSITIONED EAST OF THE MISSISSIPPI ALLOWING FOR GREATER
LARGE SCALE ASCENT FOCUSED OVER THE WESTERN OHIO VALLEY BACK INTO
THE CONFLUENT AREA OF THE OHIO AND MISSISSIPPI RIVER BETWEEN THE
MO/TN/IL AREA. THIS HAS BEEN CONSISTENTLY DEPICTED OVER THE PAST
SERIES OF FORECAST RUNS WITH THE END OF THE CURRENT 00Z CAMS SUITE
ALSO NOTING THIS PARTICULAR ZONE AS THE MORE FAVORABLE AREA OF
ORGANIZED CONVECTION WITH MULTIPLE ROUNDS ANTICIPATED.
AFTER 00Z, NOCTURNAL LLJ WILL KICK IN ACROSS THE MISSISSIPPI VALLEY
WITH THE NOSE OF THE JET ACTING AS A LOW-LEVEL CONVERGENT FEATURE
AND AIDING IN AN INCREASING REGIONAL BULK SHEAR TO PROVIDE A
NECESSARY ELEMENT TO ORGANIZE AND SUSTAIN CONVECTIVE DEVELOPMENT.
FORECAST SOUNDINGS VIA THE NAMNEST AND ECMWF ARE CONSISTENT WITH
ROBUST ASCENT WITHIN THE MID-LEVELS THANKS TO THE AMPLIFYING
TROUGH, AS WELL AS THE ADDED LOW-LEVEL CONVERGENCE WITH THE
ARRIVAL OF THE COLD FRONT AND NOSE OF THE LLJ INTO THE REGION. THIS
SIGNATURE TYPICALLY CORRELATES TO A FOCAL POINT FOR HEAVY
CONVECTION WITH BACK-BUILDING POTENTIAL UNTIL FROPA IS COMPLETE
LEADING TO SOME HEAVIER RAINFALL LINGERING FOR SEVERAL HOURS BEFORE
THE THREAT SUBSIDES. CONSIDERING PWATS BETWEEN 2-2.25" CENTERED
ACROSS THE TRI-STATE REGION OUTLINED ABOVE, AND THE ADDED ASCENT
FACTORS IN BOTH THE BOUNDARY LAYER AND MID-LEVELS (SFC-500MB),
THERE WILL LIKELY BE AN AREA THAT SEES A PERIOD OF 1-2"/HR RAINFALL
FOR AT LEAST 3-6 HRS. LEADING TO FLASH FLOOD PROSPECTS CARRYING
OVERNIGHT INTO EARLY THURSDAY MORNING. CONSISTENCY IN THE SIGNAL
HAS ALLOWED FOR A MAINTENANCE OF THE PREVIOUS SLGT RISK, HOWEVER
SOME ADJUSTMENT WAS MADE TO CONVEY MORE CERTAINTY ACROSS THE AREA
BETWEEN SOUTHEASTERN MO INTO SOUTHERN IL AND WESTERN KY/TN. SOME
AREAS ARE LIABLE TO SEE 2-4" OF RAINFALL WITH A MAX OF UP TO 6"
PLAUSIBLE CONSIDERING THE ENVIRONMENT AT LARGE.
OTHER AREAS OF CONVECTION WILL LINE UP ALONG THE FRONT AS IT
PROGRESSES SLOWLY SOUTHEAST THROUGH THE REST OF THE OHIO VALLEY,
ENTERING AREAS THAT ARE STILL IN RECOVERY FROM THE ONSLAUGHT OF
HEAVY RAINFALL THE PAST 7 DAYS. THESE STORMS ARE NOT ANTICIPATED TO
BE NEARLY AS PROLIFIC AS THE PAST SEVERAL DAYS, AND EVEN NOT AS
PROLIFIC AS WHAT WILL TRANSPIRE UPSTREAM. THAT SAID, ANTECEDENT
SOIL MOISTURE ANOMALIES APPROACHING THE 95TH PERCENTILE OVER A
LARGE AREA, PLUS THE THREAT OF SLOW MOVING CONVECTION ALONG THE
FRONT IS MORE THAN SUFFICIENT FOR A MRGL RISK CARRYING THROUGH
PARTS OF KY/IN/OH WITH THE EASTERN EXTENT INTO PORTIONS OF WV. THIS
WHOLE REGION REMAIN SENSITIVE, SO THE FORECAST WILL BE MONITORED
CLOSELY FOR ANY TARGETED UPGRADES IF TRENDS SEEM FIT.
KLEEBAUER
..SOUTHWEST INTO THE CENTRAL HIGH PLAINS
THE PREVIOUS FORECAST REMAINS ON TRACK WITH THE GLOBAL
DETERMINISTIC AND NEWEST 00Z CAMS SUITE IN AGREEMENT ON SCATTERED
THUNDERSTORM ACTIVITY LIKELY TO TRANSPIRE WEDNESDAY AFTERNOON,
CARRYING INTO THE EVENING HOURS WITH AREAS OF THE FRONT RANGE THE
MOST NOTABLE FOR SEEING MORE ORGANIZED CONVECTION THANKS TO ADDED
SHEAR AND REGIONAL ASCENT ATTRIBUTED TO A SHORTWAVE PROXY OFF THE
CENTRAL ROCKIES. SYNOPTICALLY, THE EVOLUTION OF THE SETUP ACROSS
THE SOUTHWEST AND FRONT RANGE BEGINS WITH AN UPPER RIDGE CENTERED
OVER THE FOUR CORNERS, RE- CENTERING AND AMPLIFYING WHILE AN
INVERTED TROUGH PUSHES WEST ON WEDNESDAY. THIS WILL PROMOTE A MORE
FAVORABLE SETUP FOR MONSOONAL CONVECTION AS A SURGE OF
THERMODYNAMICS (PWS ABOVE 1.25" OVERLAPPING MUCAPE OF 1000-2000
J/KG) LIFTING NORTHWARD BEHIND THE INVERTED TROUGH. AT THE SAME
TIME, WEAK SHORTWAVES EMBEDDED WITHIN THE FLOW AND ROTATING AROUND
THE RIDGE WILL PRODUCE AREAS OF LOCALLY ENHANCED ASCENT, WHICH INTO
THE IMPROVING THERMODYNAMICS SUGGESTS MORE WIDESPREAD CONVECTIVE
ACTIVITY IS LIKELY ON WEDNESDAY. WHILE A MORE SUBSTANTIAL RISK FOR
GREATER COVERAGE AND INTENSITY EXISTS JUST BEYOND D2, A LARGE MRGL
RISK FOR EXCESSIVE RAINFALL APPEARS SUPPORTED FROM THE DESERTS OF
ARIZONA NORTHEAST INTO THE CENTRAL HIGH PLAINS OF CO/KS. WITH
RAINFALL RATES OF 0.5-1"/HR LIKELY AT TIMES, AND MEAN STORM MOTIONS
OF JUST 5-10 KTS, (HIGHER IN CO BUT WITH STRONGER BULK SHEAR FOR
ORGANIZATION) THIS WILL SUPPORT AT LEAST ISOLATED INSTANCES OF
FLASH FLOODING, ESPECIALLY OVER VULNERABLE TERRAIN, URBAN AREAS, OR
RECENTLY SATURATED SOILS. A MRGL RISK REMAINS IN PLACE FOR MUCH OF
THE DESERT SOUTHWEST INTO PORTIONS OF THE CENTRAL ROCKIES THROUGH
THE COLORADO FRONT RANGE.
WEISS/KLEEBAUER
DAY 3
VALID 12Z THU AUG 20 2026 - 12Z FRI AUG 21 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE OHIO VALLEY, MID ATLANTIC, AND SOUTHWESTERN U.S...
..OHIO VALLEY TO MID ATLANTIC
TROUGHING FOR AREAS EAST OF THE MISSISSIPPI WILL CONTINUE WITH
MODEST AMPLIFICATION OCCURRING AS SHORTWAVES DIVE DOWN THE BACKSIDE
OF THE MEAN TROUGH OUT OF CANADA AND ALLOW FOR FURTHER HEIGHT FALLS
ACROSS THE OHIO VALLEY TO MID ATLANTIC. COLD FRONT FROM THE PAST
FEW PERIODS WILL CONTINUE MAKING PROGRESS TO THE EAST COAST WITH
THE FRONTAL POSITIONING A CRITICAL PART IN THE CONVECTIVE POSTURE
OVER MUCH OF THE ABOVE AREAS. THE CONSENSUS FOR FRONTAL PLACEMENT
AND EVENTUAL CONVECTIVE DEVELOPMENT PUTS THE BEST OPPORTUNITY FOR
HEAVY RAINFALL ACROSS THE TENNESSEE VALLEY AND THE NORTHERN REACHES
OF AL/MS UP THROUGH THE CENTRAL MID ATLANTIC WITH THE CORE OF
HEAVIEST RAINS FOCUSED ALONG THE DELMARVA AND VA TIDEWATER. LATEST
GLOBAL DETERMINISTIC AND ENSEMBLE MEANS NOTE A MORE ROBUST LOW-
LEVEL CONVERGENCE PATTERN INITIATING ACROSS THE COASTAL AREAS OF
THE MID ATLANTIC AS THE TIMING OF THE FRONT COUPLED WITH DIURNAL
INSTABILITY MAXIMA AND LOW-LEVEL CONVERGENCE ALONG THE WESTERN
PERIPHERY OF A RIDGE CENTERED IN THE ATLANTIC WILL ALLOW FOR A
HEAVIER AXIS OF QPF TO MATERIALIZE ON THURSDAY AFTERNOON AND
EVENING.
PROXIMITY OF THE FRONT WILL ACT AS A FOCAL POINT FOR THE SETUP
WITH THE PROJECTED LOW-LEVEL FLOW TO RUN PARALLEL TO THE FRONT OVER
AREAS OF EASTERN VA UP THROUGH THE DELMARVA PENINSULA WITH THE
NORTHERN FRINGES LINING THROUGH THE SOUTHERN HALF OF NJ. ENSEMBLE
MEAN QPF ALREADY SHOWS A SOLID 1-1.5" AREAL QPF AVERAGE WITH SOME
OF THE DETERMINISTIC FORECASTING BETWEEN 2-3" OVER THE TIME FRAME,
A TESTAMENT TO A RELATIVELY STEADY SIGNAL WITH A RELATIVELY
PRONOUNCED RANGE OF 1-3" POTENTIAL. NBM 90TH PERCENTILE IS ALSO
SOLIDLY WITHIN THAT 2-3" RANGE, ALBEIT A MUCH LARGER FOOTPRINT OF
HIGHER TOTALS WITH THE HEAVY PRECIPITATION OUTPUT EVEN DOWN INTO
NORTHERN NC. NBM PROBS FOR >2" ARE BETWEEN 20-35% ACROSS ALL OF THE
DELMARVA, EXTENDING SOUTH INTO THE NORTHERN REACHES OF THE VA
TIDEWATER. THIS SIGNAL HAS BEEN CONSISTENT THE PAST 4 CYCLES OF THE
NBM LENDING CREDENCE TO THE THREAT AS THE MEAN HASN'T REALLY
WAVERED MUCH THE PAST FEW DAYS. IN THIS CASE, THE MRGL RISK
INHERITED WAS MAINTAINED AND WILL HOLD OFF ON ANY UPGRADE UNTIL WE
GET CLOSER TO CAMS RANGE HEAVIER QPF SIGNALS MAY PRESENT THEMSELVES
IF THE SYNOPTIC EVOLUTION REMAINS FIXED TO THE AREA.
..SOUTHWEST U.S. INTO THE SOUTHERN ROCKIES
RELATIVELY TEXTBOOK MONSOONAL PATTERN ACROSS THE WEST WILL LEAD TO
SCATTERED THUNDERSTORM DEVELOPMENT ACROSS MUCH OF THE DESERT
SOUTHWEST EXTENDING NORTH INTO PARTS OF THE GREAT BASIN AND THROUGH
THE SOUTHERN ROCKIES. AS OF NOW, THE SIGNAL IS MAINLY SEASONAL WITH
REGARDS TO THE PWAT ANOMALIES AND GENERAL EXPECTATION AS THE MOST
NOTABLE AREAS WILL LIKELY BE IN THOSE TERRAIN FOCUSED ZONES ACROSS
AZ (MOGOLLON RIM), NM (SANGRE DE CRISTOS AND SACRAMENTO MTNS.), AND
UT (ZION NATIONAL PARK). LOW PROBS FOR >1" ON THE LATEST
ECENS/GEFS SUITES AND 01Z NBM ALLOW FOR A STANDARD MRGL RISK
ISSUANCE FOR THE AREA AS THE SETUP IS GENUINELY FAVORED FOR PULSE
CONVECTION AND SLOW CELL MOTIONS TIED TO THE TERRAIN AS A BROAD
597DM RIDGE CENTERS OVER THE FOUR CORNERS AND MAKES LITTLE
PROGRESSION IN THE D3 WINDOW. THE PREVIOUS MRGL WAS EXTENDED INTO
SOUTHERN UT TO ACCOUNT FOR THE INCREASING SIGNAL IN THE AREA OF
ZION NATIONAL PARK WHERE SLOT CANYONS PROVIDE AN INHERENT DANGER TO
ANY SLOW MOVING THUNDERSTORM ACTIVITY.
KLEEBAUER
DAY 4 AND DAY 5
VALID 12Z FRI AUG 21 2026 - 12Z SUN AUG 23 2026
...THERE ARE MARGINAL RISKS OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHWEST AND MID-ATLANTIC...
..EAST
HEADING INTO FRIDAY A MID TO UPPER LEVEL TROUGH WILL DEEPEN OVER
THE EASTERN U.S. RESULTING IN A SURFACE FRONTAL BOUNDARY STALLING
SOMEWHERE OVER THE MID-ATLANTIC. THIS SETUP REMAINS FAVORABLE FOR
AREAS OF HEAVY RAINFALL, AS HIGH PWS AND STRONG INSTABILITY
PERSISTS OVER PORTIONS OF THE AREA. HOWEVER, MODEL SPREAD
INTRODUCES UNCERTAINTY REGARDING THE STRENGTH AND TIMING OF
SHORTWAVES TRAVERSING THE TROUGH, AS WELL AS THE POSITIONING OF THE
SURFACE FRONT.
THE 00Z GFS, AIGFS AND CMC ARE NOTABLY MORE AGGRESSIVE IN PUSHING
THE BOUNDARY SOUTHWARD, ADVECTING DRIER AIR INTO THE NORTHERN MID-
ATLANTIC AND DISPLACING THE HEAVY RAINFALL RISK FURTHER SOUTH
ACROSS THE CAROLINAS AND FAR SOUTHERN VA. CONVERSELY, THE ECMWF
AND UKMET FEATURE A STRONGER SHORTWAVE OVER THE OH VALLEY, KEEPING
THE FRONT FURTHER NORTH AND MAINTAINING A HEAVY RAINFALL RISK
NORTHWARD INTO THE DELMARVA. GIVEN THESE LINGERING SPATIAL
DISCREPANCIES, UNCERTAINTY REMAINS REGARDING WHERE THE OPTIMAL
OVERLAP OF FORCING, INSTABILITY AND DEEP MOISTURE WILL MATERIALIZE.
WHILE THE SETUP NEEDS TO BE MONITORED CLOSELY FOR POTENTIAL
ISOLATED TO SCATTERED FLASH FLOODING, A MARGINAL RISK IS MAINTAINED
GIVEN THE LOW SPATIAL CONFIDENCE. ONLY A MINOR SOUTHWARD
ADJUSTMENT WAS MADE TO THE RISK AREA WITH THIS UPDATE...WITH A
LARGER SHIFT WITHHELD GIVEN WE'RE STILL 4 DAY OUT AND THE ECMWF
AND UKMET REMAIN NORTH.
BY SATURDAY (DAY 5) THE TROUGH DEEPENS FURTHER ACROSS THE EAST. THE
NORTHERN STREAM ENERGY APPEARS DETACHED FROM THE DEEP MOISTURE
PLUME AT THIS TIME. THUS, WHILE RAIN IS EXPECTED TO STRETCH FROM
PORTIONS OF THE OH VALLEY INTO THE NORTHEAST, IT REMAINS UNCLEAR
WHETHER RAINFALL RATES WILL BE HIGH ENOUGH TO TRIGGER FLASH
FLOODING. THE COASTAL CAROLINAS CURRENTLY REPRESENT THE MOST
FAVORABLE ZONE FOR OVERLAPPING INSTABILITY AND HIGH PWS, HOWEVER
FRONTAL TIMING AND POSITIONING ARE UNCERTAIN AT THIS 5 DAY LEAD
TIME, AND REGIONAL FFG THRESHOLDS ARE GENERALLY HIGHER ALONG THESE
COASTAL AREAS. AS A RESULT, NO ERO RISK AREA IS DELINEATED AT THIS
TIME, ALTHOUGH A MARGINAL RISK MAY NEED TO BE INTRODUCED IN
SUBSEQUENT UPDATES AS GUIDANCE TRENDS CLARIFY.
..SOUTHWEST
A MARGINAL RISK REMAINS IN PLACE ACROSS PORTIONS OF THE SOUTHWEST
FOR BOTH FRIDAY AND SATURDAY, WITH THE RISK EXPANDING SLIGHTLY
NORTHWESTWARD ON SATURDAY RELATIVE TO FRIDAY. A STRONG UPPER LEVEL
RIDGE WILL REMAIN ANCHORED OVER THE REGION, TRAPPING EMBEDDED
SHORTWAVE ENERGY WITHIN THE LIGHT FLOW. PLENTIFUL MONSOONAL
MOISTURE AND INSTABILITY WILL REMAIN IN PLAY, MAKING LOCALIZED
FLASH FLOODING LIKELY BOTH DAYS. BECAUSE CONVECTIVE FORCING WILL BE
PRIMARILY TERRAIN INDUCED, OVERALL STORM COVERAGE SHOULD STAY
BELOW SLIGHT RISK THRESHOLDS. HOWEVER TRENDS WILL CONTINUE TO BE
MONITORED, AS ANY INCREASE IN CONVECTIVE COVERAGE/ORGANIZATION
WITHIN THE FAVORABLE CAPE/PW FOOTPRINT COULD SUPPORT A MORE
CONCENTRATED FLASH FLOOD RISK.
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
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