463
FOUS30 KWBC 092022
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
422 PM EDT THU JUL 9 2026
DAY 1
VALID 16Z THU JUL 09 2026 - 12Z FRI JUL 10 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF
THE CENTRAL HIGH PLAINS TO THE MID-ATLANTIC...
..16Z UPDATE
ONLY A FEW CHANGES WERE NEEDED WITH THIS UPDATE. THE LATEST
GUIDANCE SUGGESTS A HIGHER THREAT OF EXCEEDING FLASH FLOOD GUIDANCE
ACROSS CENTRAL NEW JERSEY UP TO THE JERSEY SUBURBS OF NYC, DUE TO
STRONG STORMS MOVING THROUGH THIS AFTERNOON INTO THIS EVENING. FOR
THAT REASON, AND DUE TO URBAN CONCERNS ALONG I-95, THE SLIGHT RISK
WAS EXTENDED NORTHEASTWARD TO STATEN ISLAND.
A HIGHER-END SLIGHT WAS EXTENDED WEST ALONG I-66 INTO THE NORTHERN
SHENANDOAH VALLEY WITH THIS UPDATE, AS WELL AS INTO CENTRAL JERSEY,
NEAR TRENTON. EXPECT INCREASING CHANCES OF FLOODING WITH
BACKBUILDING STORMS IN THESE AREAS THIS AFTERNOON. AVERAGE SOIL
MOISTURE IN THIS AREA FROM RECENT HEAVY RAINS WILL ALSO SUPPORT A
BIT HIGHER THREAT FOR FLASH FLOODING.
NO CHANGES WERE MADE TO THE SLIGHT RISKS ACROSS THE MID-MISSISSIPPI
AND LOWER OHIO VALLEYS. MCSS EXPECTED IN THESE AREAS MOVING OVER
AREAS OF SATURATED SOILS FROM HEAVY RAINS WILL ALSO LEAD TO WIDELY
SCATTERED INSTANCES OF FLASH FLOODING LATE THIS AFTERNOON THROUGH
THIS EVENING.
WEGMAN
..PREVIOUS DISCUSSION
..MID-ATLANTIC
MOISTURE AND INSTABILITY WILL INCREASE TODAY AHEAD OF A MID-LEVEL
SHORTWAVE TRACKING THROUGH THE AREA DURING PEAK HEATING. PW VALUES
ARE FORECAST TO EXCEED 2" ALONGSIDE SBCAPE OVER 2000 J/KG, A
FAVORABLE PROFILE FOR HEAVY RAINFALL RATES. WHILE CONVECTION IS
EXPECTED TO EVENTUALLY CONSOLIDATE INTO A FORWARD PROPAGATING
CONVECTIVE LINE OR CLUSTER, SCATTERED THUNDERSTORMS SHOULD DEVELOP
INITIALLY FROM NORTHERN VA INTO SOUTHEAST PA. CELL MERGERS ARE
POSSIBLE WITH THIS INITIAL ACTIVITY AND AS THE UPSTREAM CONVECTIVE
LINE/CLUSTERS ARRIVE.
WITH BOTH THE REFS AND HREF SHOWING LOCALLY HEAVY RAIN AND 15%+
FFG EXCEEDANCE PROBABILITIES, THE SLIGHT RISK WAS EXPANDED
WESTWARD INTO MORE OF SOUTHERN PA AND PORTIONS OF WV. THE HIGHEST
EAS PROBABILITIES FROM THE HREF/REFS POINT TO AN AXIS ACROSS
NORTHEAST MD, SOUTHEAST PA, SOUTHERN NJ AND DE AS THE MOST FAVORED
CORRIDOR FOR CONCENTRATED HEAVY RAINFALL. NEIGHBORHOOD
PROBABILITIES FROM BOTH ENSEMBLE SUITES INDICATE A 50-80% CHANCE OF
LOCALLY EXCEEDING 3" OF RAIN, A 15-30% CHANCE OF EXCEEDING 5", AND
A 30-50% CHANCE OF 2"'HR RAINFALL. GIVEN THE IMPRESSIVE CAPE/PW
OVERLAP, WHEREVER CLUSTERS MANAGE TO MERGE AND BRIEFLY TRAIN, SOME
FLASH FLOODING IS LIKELY AND CONSIDER THIS A HIGHER END SLIGHT
RISK. LOCALLY SIGNIFICANT URBAN FLASH FLOOD IMPACTS ARE POSSIBLE
IF HEAVIER CELLS END UP OVER A SENSITIVE URBAN LOCATION.
..MID MS VALLEY INTO THE OH VALLEY
MORNING CONVECTION MOVING ACROSS MO IS EXPECTED TO WEAKEN, HOWEVER
ROBUST REDEVELOPMENT IS EXPECTED BY THIS AFTERNOON AHEAD OF A
SHORTWAVE EXTENDING FROM MO INTO IL. WHILE CELLS SHOULD GENERALLY
REMAIN PROGRESSIVE AS THEY TRACK EASTWARD, BRIEF CELL MERGERS COULD
LOCALLY ELEVATE THE FLASH FLOOD THREAT. THE 00Z HREF AND REFS ARE
IN GOOD AGREEMENT THAT SOUTHEAST MO, SOUTHERN IL AND WESTERN KY
WILL SEE THE MOST CONCENTRATED HEAVY RAINFALL AXIS. AS A
STRENGTHENING LOW LEVEL JET BOOSTS MOISTURE TRANSPORT THIS
EVENING, THE SOUTHERN TAIL OF THE CONVECTIVE LINE MAY HANG UP,
ALLOWING FOR A PERIOD OF BACKBUILDING AND TRAINING. HREF/REFS
NEIGHBORHOOD PROBABILITIES SHOW A 40-70% CHANCE OF RAINFALL LOCALLY
EXCEEDING 3" ALONG THIS AXIS. SCATTERED FLASH FLOODING APPEARS
LIKELY GIVEN THIS SETUP, ALTHOUGH JUST ENOUGH SOUTHWARD PROPAGATION
OF CONVECTION MAY CAP RAINFALL TOTALS AND KEEP THE FLASH FLOOD
RISK FROM BEING EVEN HIGHER.
..CENTRAL HIGH PLAINS
MID-LEVEL SHORTWAVE ENERGY COMBINED WITH UPPER JET SUPPORT WILL
PRODUCE CONVECTION ACROSS THE HIGH PLAINS FROM CO TO SD THIS
AFTERNOON. DEEP LAYER SHEAR AND INSTABILITY SHOULD BE SUFFICIENT TO
SUPPORT SLOW MOVING SUPERCELLS CAPABLE OF POCKETS OF INTENSE
RAINFALL AND LOCALIZED FLASH FLOODING. WITH STORM MOTION VECTORS
QUITE WEAK, MOST HIGH RES MODELS SEEM TOO QUICK IN MOVING THIS
ACTIVITY OFF TO THE EAST (A COMMON BIAS). CONVECTION WILL
EVENTUALLY SHIFT EAST BY TONIGHT, AND A MAJORITY OF THE 00Z HIGH
RES MODELS SUPPORT SOME UPSCALE GROWTH AS IT MOVES INTO WESTERN AND
CENTRAL KS. PORTIONS OF EASTERN CO, SOUTHWEST NE AND
WESTERN/CENTRAL KS HAVE BEEN UPGRADED TO A SLIGHT RISK WITH
ISOLATED TO SCATTERED FLASH FLOODING POSSIBLE.
..ARIZONA
CONVECTION DEVELOPING OVER THE HIGHER TERRAIN MAY PROPAGATE
SOUTHWESTWARD INTO THE LOWER DESERTS DURING THE LATE AFTERNOON AND
EVENING HOURS. UNCERTAINTIES PERSIST REGARDING STORM PROPAGATION
SPEED (WHETHER CELLS WILL MOVE TOO QUICKLY TO PRODUCE ANY
FLOODING) AND THE EXACT SPATIAL EXTENT/MAGNITUDE OF INSTABILITY.
WHILE THE OVERALL THREAT LOOKS MORE ROBUST LATER THIS WEEK INTO
THE WEEKEND, WE WILL MAINTAIN THE INHERITED MARGINAL RISK.
CHENARD
DAY 2
VALID 12Z FRI JUL 10 2026 - 12Z SAT JUL 11 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF
THE MID MISSISSIPPI VALLEY INTO THE CENTRAL APPALACHIANS...
..2030Z UPDATE
NO MAJOR CHANGES WERE NEEDED TO THE ONGOING RISK AREAS ACROSS THE
OHIO AND TENNESSEE VALLEYS. AS IS TYPICAL FOR THIS TIME OF YEAR,
MCS ACTIVITY WILL BE RESPONSIBLE FOR MOST OF THE FLOODING CONCERNS
IN THIS AREA. AS IS ALSO TYPICAL, THE GUIDANCE CONTINUES TO SHIFT
SOUTH WITH WHERE THE EXPECTED TRACK OF THE MCS IS. THUS, THE SLIGHT
RISK AREA AND AN EMBEDDED HIGHER-END SLIGHT WERE ADJUSTED
SOUTHWARD, WHICH RESULTED IN DOWNGRADES OVER PORTIONS OF THE OHIO
VALLEY, AND UPGRADES IN SOUTHERN TENNESSEE. ELSEWHERE, NO MAJOR
CHANGES WERE MADE.
WEGMAN
..MID MS VALLEY TO THE CENTRAL APPALACHIANS
A FAVORABLE ENVIRONMENT FOR CONVECTIVE TRAINING AND BACKBUILDING
SHOULD TAKE SHAPE ACROSS PORTIONS OF THE OH AND TN VALLEY ON
FRIDAY. MULTIPLE SHORTWAVES EMBEDDED WITHIN THE WEST TO NORTHWEST
FLOW ALOFT WILL INTERACT WITH A PERSISTENT WESTERLY LOW LEVEL
MOISTURE TRANSPORT VECTOR. THIS WIND PROFILE WILL RESULT IN VERY
WEAK CORFIDI VECTORS, AND THUS UPWIND PROPAGATION AND BACKBUILDING
INTO THE LOW LEVEL FLOW IS PROBABLE. THIS SETUP WILL OVERLAP AN
UNSTABLE AND MOIST AIRMASS, WITH PWS FORECAST AROUND OR OVER 2".
SOME UNCERTAINTY REMAINS REGARDING CONVECTIVE EVOLUTION,
ESPECIALLY HOW MORNING CONVECTION AFFECTS AFTERNOON
DESTABILIZATION AND EXACTLY WHERE THE INSTABILITY AXIS RECOVERS
AND SETS UP. THERE ARE ALSO SOME DIFFERENCES IN THE
STRENGTH/TIMING OF THE CONVECTIVELY ENHANCED SHORTWAVE THAT WILL
BE TRACKING INTO THE AREA FROM THE WEST. THE CURRENT MODEL
CONSENSUS CONSISTING OF THE ECENS/GEFS/AIFS/AIGFS FAVORS MUCH OF KY
INTO NORTHERN TN FOR THE AXIS OF HEAVIEST RAIN. A HIGHER END
SLIGHT RISK WILL COVER THESE AREAS, WITH THE CAVEAT THAT THE EXACT
AXIS WILL LIKELY REQUIRE SOME SPATIAL ADJUSTMENTS IN FUTURE
UPDATES. WILL NEED TO CONTINUE TO CLOSELY MONITOR THE EVOLUTION OF
THIS THREAT, AS A SETUP SUCH AS THIS COULD RESULT IN AN EVENTUAL
MDT RISK PENDING MODEL TRENDS.
..HIGH PLAINS
ADDITIONAL SHORTWAVE ENERGY EJECTING OUT OF THE ROCKIES WILL
TRIGGER ANOTHER ROUND OF CONVECTION FROM THE TX PANHANDLE INTO CO
AND KS. THE LOW LEVEL JET AND OVERALL FORCING MAY BE A BIT WEAKER
THAN THURSDAY, WHICH MAY LIMIT THE DEGREE OF ORGANIZATION AND
UPSCALE GROWTH. NONETHELESS, SOME SLOW CELL MOTIONS AND HIGH
RAINFALL RATES WILL MAINTAIN A THREAT FOR LOCALIZED FLASH FLOOD
IMPACTS.
..ARIZONA
THE SYNOPTIC AND MESOSCALE SETUP ON FRIDAY WILL BE VERY SIMILAR TO
DAY 1, ALTHOUGH INSTABILITY MAYBE SLIGHTLY HIGHER. BOTH THE RRFS
AND REFS DEPICT MORE ROBUST CONVECTIVE DEVELOPMENT CAPABLE OF
PRODUCING LOCALIZED RAINFALL TOTALS OVER 2 INCHES. WHILE THIS RISK
SHOULD REMAIN ISOLATED, THE FLASH FLOOD THREAT APPEARS SLIGHTLY
HIGHER THAN ON THURSDAY.
CHENARD
DAY 3
VALID 12Z SAT JUL 11 2026 - 12Z SUN JUL 12 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE OHIO/TENNESSEE VALLEYS AND CENTRAL APPALACHIANS...
..2030Z UPDATE
ADDITIONAL MCS AND OTHER STORM ACTIVITY IS EXPECTED ONCE AGAIN ON
SATURDAY ACROSS THE TENNESSEE VALLEY. AT THIS TIME IT APPEARS
SHOULD A MODERATE RISK UPGRADE BE EVENTUALLY NEEDED, IT WILL BE ON
SATURDAY IN THE TENNESSEE VALLEY, FOLLOWING MULTIPLE DAYS OF
RAINFALL OVER THIS SAME AREA, AND ADDING URBAN AND TOPOGRAPHICAL
EFFECTS INTO THE EQUATION. EXPECTED RAINFALL IN THIS AREA IS LITTLE
CHANGED WITH THIS UPDATE. IT'S ALSO LIKELY THAT SOUTHWARD
ADJUSTMENTS MAY BE NEEDED AS WELL WITH FUTURE UPDATES AS THIS
PERIOD MOVES INTO THE CAMS RANGE AND NOTING THE FREQUENT TENDENCY
IN THE GUIDANCE TO SHIFT THE AXIS OF HEAVIEST RAINFALL WITH ANY
MCS'S SOUTH. THIS MAY HELP LOWER THE FLOODING RISK OVERALL,
DEPENDING ON THE MAGNITUDE OF ANY FUTURE SOUTHWARD ADJUSTMENTS, BUT
IT'S ALSO POSSIBLE THAT CITIES FURTHER TO THE SOUTH TO INCLUDE
ATLANTA AND BIRMINGHAM WILL HAVE AN INCREASING FLASH FLOODING RISK
IF THE AXIS OF HEAVIEST RAINFALL ADJUSTS CLOSER. REGARDLESS, THERE
WILL BE NO SHORTAGE OF MOISTURE FOR THE STORMS TO WORK WITH ON
SATURDAY, SO COVERAGE AND INSTABILITY WILL ULTIMATELY DETERMINE
HOW SEVERE ANY FLASH FLOODING IN THIS AREA ENDS UP BEING.
WEGMAN
..OH AND TN VALLEY
THE FAVORABLE HEAVY RAINFALL PATTERN WILL PERSIST INTO SATURDAY
ACROSS PORTIONS OF THE OH AND TN VALLEY. DEEP LAYER WESTERLY FLOW,
PERSISTENT LOW LEVEL MOISTURE TRANSPORT, AND WEAK CORFIDI VECTORS
WILL SUPPORT THE POTENTIAL FOR TRAINING/BACKBUILDING CELLS. WHILE
CONVECTIVE SCALE DETAILS REMAIN UNCERTAIN THIS FAR OUT, LARGE
SCALE FORCING WILL BE STRONG, WITH A WELL DEFINED MID LEVEL
SHORTWAVE DIVING SOUTHEAST INTO THE REGION BENEATH THE RIGHT
ENTRANCE REGION OF AN UPPER LEVEL JET STREAK.
ORGANIZED CONVECTION WITHIN AN AIRMASS CHARACTERIZED BY PWS AROUND
2" WILL SUPPORT HEAVY RAINFALL RATES. GIVEN THE POTENTIAL FOR
TRAINING AND BACKBUILDING IN THIS ENVIRONMENT, SOME FLASH FLOODING
AGAIN APPEARS LIKELY. THE EXACT HEAVY RAINFALL AXIS IS UNCLEAR AND
WILL DEPEND ON LEFTOVER MESOSCALE BOUNDARIES AND THE EXACT
STRENGTH/TRACK OF THE SHORTWAVE, BUT AN AREA FROM TN AND KY INTO WV
APPEARS MOST AT RISK. THIS IS A SOLID SLIGHT RISK, WITH ISOLATED
TO SCATTERED FLASH FLOODING EXPECTED. IF THIS AXIS ENDS UP
OVERLAPPING WITH HEAVY RAINFALL FROM DAY 2, THEN A HIGHER RISK
CATEGORY MAY EVENTUALLY BE REQUIRED.
..SOUTHWEST
THE TERRAIN DRIVEN CONVECTIVE PATTERN WILL CONTINUE ACROSS AZ,
WITH STORMS ROLLING OFF THE TERRAIN AND INTO AN INSTABILITY POOL
OVER SOUTHERN AZ. BOTH INSTABILITY AND PWS SHOULD BE HIGHER
SATURDAY THAN PRIOR DAYS, WHICH SHOULD DRIVE GREATER CONVECTIVE
COVERAGE AND AT LEAST ISOLATED FLASH FLOODING. TRENDS WILL BE
MONITORED, WITH A SLIGHT RISK UPGRADE IN FUTURE CYCLES A
POSSIBILITY.
CHENARD
DAY 4 AND DAY 5
VALID 12Z SUN JUL 12 2026 - 12Z TUE JUL 14 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ALONG PARTS OF THE
CENTRAL GULF COAST ON MONDAY...
A FRONTAL BOUNDARY WILL BE ADVANCING SOUTHWARD THROUGH THE MIDWEST,
TENNESSEE VALLEY AND SOUTHEAST WHICH WILL BE A FOCUS FOR SCATTERED
CONVECTION SUNDAY AND MONDAY. ANY OF THESE THUNDERSTORMS HAVE THE
POTENTIAL TO PRODUCE POCKETS OF HEAVY RAINFALL THAT COULD LEAD TO
ISOLATED INSTANCES OF FLASH FLOODING GIVEN THE MOISTURE RICH
ATMOSPHERE...WITH PRECIPITABLE WATER VALUES IN THE 1.8 TO 2.2
INCHES...SOUTH OF THE FRONT. A MARGINAL RISK WAS MAINTAINED FOR
THE SUNDAY FROM EASTERN TEXAS AND OKLAHOMA TO THE MID-ATLANTIC AND
SOUTHEAST, WHILE A SLIGHT RISK AREA WAS INTRODUCED NEAR THE GULF
COAST AS LOW LEVEL WINDS TURN SOUTHERLY AND RESULTS IN A REGION OF
ENHANCED MOISTURE FLUX CONVERGENCE NEAR THE BOUNDARY.
INCREASING SOUTHERLY FLOW AROUND THE WESTERN PERIPHERY OF THE
CENTRAL U.S. RIDGE WILL DRAW MOISTURE INTO THE SOUTHERN FOUR
CORNERS AND GREAT BASIN LATER THIS WEEKEND INTO EARLY NEXT WEEK.
THIS MOISTURE WILL LIKELY LEAD TO THE DEVELOPMENT OF SCATTERED TO
NUMEROUS SHOWERS AND THUNDERSTORMS WITH THE POTENTIAL TO PRODUCE
HEAVY RAINFALL AND LOCALIZED FLASH FLOODING. A MARGINAL RISK WAS
MAINTAINED ACROSS PORTIONS OF ARIZONA AND NEW MEXICO FOR BOTH DAY
4 AND DAY 5.
CAMPBELL/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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