371
FOUS30 KWBC 210824
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
424 AM EDT FRI AUG 21 2026
DAY 1
VALID 12Z FRI AUG 21 2026 - 12Z SAT AUG 22 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
VIRGINIA AND THE CAROLINAS...
..VIRGINIA TO CAROLINAS
FOR THE SOUTHERN MID-ATLANTIC, THE 21/00Z CAMS REMAINED
CONSISTENT WITH THE 20/12Z CAMS IN SHOWING SOLID COVERAGE 2-4"
AMOUNTS ACROSS CENTRAL NC INTO ADJACENT NORTH- CENTRAL SC, WITH
LOCALIZED MAXIMUM AMOUNTS IN EXCESS OF 6 INCHES. HREF/REFS
NEIGHBORHOOD PROBABILITIES FOR >5" ARE NOW 30-60%. THIS INCLUDES
THE SANDHILLS OF THE CAROLINAS WHERE FFGS ARE HIGHER, BUT ALSO
EXTENDS INTO THE PIEDMONT WHERE TERRAIN IS MORE AT RISK FOR FLASH
FLOODING. THE PICTURE WAS SIMILAR IN THE HREF/REFS WITH RESPECT TO
PLACEMENT OF THE PROBABILITIES OF 2 INCH ACCUMULATION PER HOUR
LATER THIS AFTERNOON IN TERMS OF PLACEMENT BUT NOTICEABLY VARIABLE
IN TERMS OF NEIGHBORHOOD PROBABILITIES. ENVIRONMENTAL CONDITIONS
WILL REMAIN VERY BUOYANT WITH PWATS BETWEEN 2-2.3" FOR THE ENTIRE
AREA ALONG AND SOUTH OF A QUASI-STATIONARY FRONT. GLOBAL-SCALE MODELS
REMAINED CONSISTENT WITH THEIR SIGNATURE OF 1-2" OF RAINFALL ON AN
AREAL AVERAGE BASIS WITH SOME OF THE DETERMINISTIC OUTPUTS
APPROACHING UPWARDS OF 3-5" AND SUPPORTIVE OF THE PREVIOUSLY ISSUED
SLIGHT RISK AREA WITH ONLY MINOR MODIFICATIONS NEEDED...ESPECIALLY
IN MORE URBANIZED ZONES ALONG I-95 AND POINTS EAST. MAINTAINED
THE HIGH-END SLGT WORDING AS THE THREAT FOR LOCALLY SIGNIFICANT
RAINFALL >4" PERSISTS.
..SOUTHWEST
MONSOONAL ACTIVITY WILL CONTINUE FOR YET ANOTHER DAY AS THE
SOUTHWEST CONUS LIES UNDERNEATH A BROAD RIDGE CENTERED OVER THE
FOUR CORNERS WITH MULTIPLE MID-LEVEL VORTICITY MAXIMA PIVOTING
UNDER THE RIDGE AXIS. SEASONAL TO SLIGHTLY ELEVATED PWATS WILL
EXTEND THROUGHOUT THE SOUTHWEST, EVEN REACHING A BIT FARTHER NORTH
INTO THE GREAT BASIN LEADING TO SOME LOCALLY HEAVY RAINFALL EVEN
MAKING ITS PRESENCE INTO PORTIONS OF NV AND CENTRAL UT WHILE ALSO
IMPACTING THOSE SAME AREAS THAT SAW ACTIVITY THE PRIOR PERIOD.
LOCAL TOTALS OF 1-2" ARE FORECAST. BUT AREAL QPF AVERAGE IS PRETTY
MUCH BETWEEN 0.25-0.5" WHICH IS TYPICAL FOR THESE TYPES OF SETUPS.
A BROAD MRGL REMAINED IN PLACE FOR MUCH OF THE DESERT SOUTHWEST UP
INTO THE GREAT BASIN...EXTENDING EAST INTO PARTS OF THE SOUTHERN
ROCKIES.
BANN
DAY 2
VALID 12Z SAT AUG 22 2026 - 12Z SUN AUG 23 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG MUCH OF THE
EAST COAST, AND OVER THE WESTERN U.S...
..EAST COAST
LARGE SCALE PATTERN WILL CONTINUE ITS EVOLUTION INTO A MUCH MORE
AMPLIFIED SETUP WITH A DEEPENING MID-LATITUDE TROUGH EXTENDING FROM
CANADA ALL THE WAY INTO THE EASTERN CONUS. THIS PLACES THE ENTRANCE
REGION OF AN UPPER LEVEL JET IN FAVORABLE POSITION OVER AN AIRMASS
WITH PRECIPITABLE WATER VALUES OF 2 TO 2.25 INCHES AS A FEW ROBUST
DISTURBANCES ROTATE AROUND THE LEADING EDGE OF THE TROUGH WHICH
WILL SUPPORT HEAVY RAINFALL ALONG THE EASTERN SEABOARD. CURRENT
MODEL CONSENSUS IS A MODERATE TO HEAVY QPF FOOTPRINT EXTENDING FROM
COASTAL SC ALL THE WAY UP INTO ME. PRIMARY CONCERN FOR EXCESSIVE
RAINFALL IS ALONG AND EAST OF I-95 IN THE MID- ATLANTIC DUE TO THE
HEAVY/EXCESSIVE RAIN THAT OCCURRED ON THURSDAY AS MUCH AS THE WITH
EXPECTED RAINFALL AMOUNTS IN THE DAY 2 PERIOD.
..WEST
PERSISTENT RIDGING ACROSS THE WESTERN U.S. WILL FINALLY BEGIN TO
SHIFT BACK OVER THE PLAINS AS A ROBUST TROUGH OVER THE PACIFIC
OCEAN MAKES HEADWAY INTO THE PACIFIC NORTHWEST AND BEGINS PUSHING
THE PATTERN DOWNSTREAM AND FLATTENING THE RIDGE UP TOP. THE
PROGRESSION OF THE TROUGH WILL LEAD TO AN INFLUX OF BOTH REGIONAL
MOISTURE AND ASCENT AS THE TROUGH MAKES PROGRESS INTO OR/WA AS WE
MOVE INTO THE MIDDLE PART OF THE WEEKEND. PWAT ANOMALIES ARE
ANTICIPATED TO SURGE UPWARDS OF 2-3 STANDARD DEVIATIONS ABOVE
NORMAL FOR THIS TIME OF YEAR AS FAR NORTH AS IDAHO AND WESTERN
MONTANA WITH THE REST OF THE WEST FIRMLY ENTRENCHED WITHIN A +1
STANDARD DEVIATION PWAT ANOMALY, GOOD ENOUGH TO MAINTAIN A
PERSISTENT MONSOONAL TYPE PATTERN OVER THE DESERT SOUTHWEST AND
GREAT BASIN INTO THE CENTRAL ROCKIES. A BROAD MRGL RISK OVER MUCH
OF THE WESTERN U.S, EAST OF THE PACIFIC COAST STATES WILL SUFFICE.
BANN
DAY 3
VALID 12Z SUN AUG 23 2026 - 12Z MON AUG 24 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE
NORTHEASTERN US/CENTRAL US AND THE DESERT SOUTHWEST...
NORTHEAST...
CYCLOGENESIS NORTH OF THE GREAT LAKES WILL HELP PUSH A COLD FRONT
EASTWARD ACROSS NEW ENGLAND ON SUNDAY. UNTIL IT CLEARS THE
AREA...SOUTHERLY FLOW AHEAD OF THE FRONT WILL CONTINUE TO DRAW AN
AIRMASS WITH PRECIPITABLE WATER VALUES OF 1.8 TO 2.2 INCHES ACROSS
THE COASTAL REGION. THIS SHOULD SUPPORT A LOW-END RISK OF EXCESSIVE
RAINFALL MAINLY WHERE LOW LEVEL FLOW INTERACTS WITH THE TERRAIN.
NOTE THAT THE AREAL COVERAGE OF THE MARGINAL RISK AREA HAS
DECREASED IN RESPONSE TO THE QUICKER FORWARD SPEED COMPARED WITH
PREVIOUS RUNS.
MIDWEST...
ENERGY APPROACHING FROM THE WEST BEGINS TO FLATTEN THE NORTHERN
PORTION OF THE RIDGE...ALLOWING FOR SHOWERS AND THUNDERSTORMS TO
DEVELOP ACROSS THE NORTHERN PLAINS WHICH CAN BUILD SOUTHEAST INTO
THE OZARKS. GIVEN THE POTENTIAL FOR REPEAT CONVECTION...MAINTAINED
THE MARGINAL RISK AREA EVEN THOUGH INDIVIDUAL CELLS SHOULD BE
PROGRESSIVE.
WESTERN US...
THE OVERALL PATTERN IS EXPECTED TO REMAIN RELATIVELY UNCHANGED
WITH THE UPPER RIDGE REMAINED ANCHORED OVER THE SOUTHWEST AND
SOUTHERN PLAINS. MOISTURE AND ENERGY MOVING ALONG THE WESTERN AND
NORTHERN PERIPHERY OF THE RIDGE WILL CONTRIBUTE TO DAILY SHOWER AND
THUNDERSTORM ACTIVITY AND THE POTENTIAL FOR ISOLATED FLASH
FLOODING EXTENDING FROM THE SOUTHWEST TO THE NORTHERN INTERMOUNTAIN
WEST AND ROCKIES.
BANN
DAY 4 AND DAY 5
VALID 12Z MON AUG 24 2026 - 12Z WED AUG 26 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHWEST, INTERMOUNTAIN WEST, AND ROCKIES DAYS 4/5 AND THE
CENTRAL PLAINS DAY 5...
AN UPPER RIDGE WILL REMAIN ANCHORED OVER THE SOUTHWEST-SOUTHERN
PLAINS INTO MIDWEEK, WITH MOISTURE AND ENERGY ON THE BACKSIDE OF
THE HIGH CONTRIBUTING TO DIURNAL SHOWERS AND STORMS THAT WILL RAISE
THE POTENTIAL FOR ISOLATED FLASH FLOODING BOTH DAYS FROM PARTS OF
THE SOUTHWEST TO THE NORTHERN ROCKIES.
AREAS OF HEAVY RAINFALL LEADING TO POTENTIAL FLASH FLOODING ARE
EXPECTED TO DEVELOP ACROSS PORTIONS OF THE CENTRAL PLAINS TUESDAY
INTO EARLY WEDNESDAY AS SHORTWAVES EMANATING FROM THE WEST SPILL
OFF OF THE TOP OF THE RIDGE. UNCERTAINTY IN THE TIMING AND
PLACEMENT OF THESE FEATURES LIMITED CONFIDENCE IN THE LOCATION OF
THESE HEAVIER AMOUNTS. HOWEVER, A CORRIDOR OF DEEPENING MOISTURE
AND INCREASING INSTABILITY ALONG A COLD FRONT DROPPING SOUTH INTO
THE REGION, COMBINED WITH THE POTENTIAL FOR TRAINING, PROMPTED THE
INTRODUCTION OF THE MARGINAL RISK AREA EXTENDING EAST OF THE
ROCKIES ACROSS PORTIONS OF THE CENTRAL PLAINS ON DAY 5.
PEREIRA
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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