688
FOUS30 KWBC 181906
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
306 PM EDT SAT JUL 18 2026
DAY 1
VALID 16Z SAT JUL 18 2026 - 12Z SUN JUL 19 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF
WEST TEXAS THROUGH THE EASTERN GREAT BASIN, AS WELL AS PARTS OF THE
NORTHEAST AND MID-ATLANTIC...
..WESTERN TEXAS TO THE FOUR CORNERS/GREAT BASIN
MONSOON RIDGE WILL BECOME FAVORABLY ALIGNED TO DRAW IMPRESSIVE
THERMODYNAMICS NORTHWARD FROM MEXICO, REACHING FROM WEST TEXAS
THROUGH MUCH OF THE DESERT SOUTHWEST AND THEN NORTHWARD INTO THE
GREAT BASIN AND INTERMOUNTAIN WEST. MULTIPLE WEAK SHORTWAVES
EMBEDDED WITHIN THE FLOW WILL CONTINUE TO PROGRESS ANTI-
CYCLONICALLY AROUND THIS RIDGE, BRINGING LOCALLY ENHANCED ASCENT
TO THE REGION, WITH A FEW OF THESE IMPULSES NOTED ON MORNING WV
IMAGERY IN TX AND NM. WHILE ANY OF THESE IMPULSES WILL LOCALLY
ENHANCE ASCENT LEADING TO CLUSTERS OF MORE ORGANIZED CONVECTION
TODAY, THE GREATEST RISK IS JUST THE BREADTH OF COVERAGE OF
THUNDERSTORMS WITH POTENTIALLY HEAVY RAINFALL TODAY.
PWS THIS MORNING ARE IMPRESSIVE ACROSS THE REGION, MEASURED VIA GPS
AND MORNING RAOBS VARY FROM AROUND 1.2 INCHES AT SLC TO AS HIGH AS
2.1 INCHES AT PHX, AT OR ABOVE THE 90TH PERCENTILE ACROSS A LARGE
AREA (AND AS HIGH AS +3 SIGMA), AND THAT MEASURED PW AT PHX THIS
MORNING IS A DAILY RECORD. AT THE SAME TIME INSTABILITY IS PROGGED
TO CLIMB TO 1000-2000 J/KG, LOCALLY EVEN HIGHER, AS FAR AS 40N
LATITUDE IN THE FOUR CORNERS, WHICH IS IMPRESSIVE AND IS A TYPICAL
DISCRIMINATOR OF MORE WIDESPREAD MONSOONAL HEAVY RAIN/FLASH FLOOD
DAYS.
THE CAMS, INCLUDING THE UA WRF, ARE AGGRESSIVE WITH COVERAGE OF
THEIR SIMULATED REFLECTIVITY ACROSS MUCH OF THE AREA TODAY, WITH
HOURLY RAINFALL POTENTIALLY REACHING 1.5 TO 2.5 INCHES. THIS COULD
EASILY EXCEED THE 1-HR FFG ACROSS THE REGION, AND IN SOME AREAS THE
3-HR FFG EVEN HAS A HIGH CHANCE (40-60%) OF BEING EXCEEDED WHERE
TERRAIN-TYING OR BOUNDARY-COLLISIONS CAN CAUSE A TEMPORAL EXTENSION
OF THE HEAVY RAIN RATES. WITH STORM MOTIONS GENERALLY EXPECTED TO
BE WEAK AT 5-10 KTS AND CHAOTIC, AN ACTIVE DAY IS EXPECTED, WITH
SCATTERED FLASH FLOODING EXPECTED, ESPECIALLY ACROSS VULNERABLE
FEATURES LIKE BURN SCARS, SLOT CANYONS, AND URBAN AREAS.
THE INHERITED SLGT RISK WAS MODIFIED TO ACCOUNT FOR RECENT
GUIDANCE, AND THERE WAS SOME CONSIDERATION OF AN INCREASED RISK
BASED ON THE IMPRESSIVE REFS EXCEEDANCE PROBABILITIES WHICH RISE
ABOVE 55% FOR FFG, BUT THE MORE MUTED HREF WAS USED MORE HEAVILY,
ESPECIALLY SINCE THE HIGHEST FFG EXCEEDANCE IS ACROSS THE HIGHER
ELEVATIONS OF THE MOGOLLON RIM AND NOT DOWN INTO THE DESERTS
(ALTHOUGH AN EXPANSION SW INTO SOME LOWER TERRAIN WAS MADE WITH
THIS UPDATE).
..MIDWEST TO THE MID ATLANTIC AND NORTHEAST
A COLD FRONT WILL DROP STEADILY SOUTHEAST FROM THE GREAT LAKES,
REACHING THE LOWER OHIO VALLEY AND THE MID-ATLANTIC BY SUNDAY
MORNING. AHEAD OF THIS FRONT, IMPRESSIVE MOISTURE WILL POOL FROM
KENTUCKY EASTWARD TO LONG ISLAND AND CAPE COD, WHERE PWS ARE
ALREADY 1.75 TO 2.0 INCHES AND WILL CLIMB ABOVE 2.0 INCHES THROUGH
THIS AFTN. THE OVERLAP OF THIS ELEVATED PW WITH INCREASING SBCAPE
(2000-3000 J/KG FORECAST) WILL CREATE ROBUST THERMODYNAMICS WHICH
WILL SUPPORT WIDESPREAD CONVECTION CAPABLE OF PRODUCING INTENSE
HOURLY RAINFALL FOR WHICH THE HREF AND REFS SUGGEST HAS A 40-60%
(10-15% CHANCE) OF EXCEEDING 1 INCH (2 INCHES).
THE EXCESSIVE RAINFALL RISK WILL STEADILY INCREASE THROUGH THE AFTN
AND CONTINUE INTO THIS EVENING/TONIGHT AS MULTIPLE ROUNDS OF
THUNDERSTORMS DEVELOP AND TRACK ACROSS THE AREA. 0-6KM BULK SHEAR IS
PROGGED TO INCREASE TO 30-40 KTS AHEAD OF THE COLD FRONT, AND AS
WEAK IMPULSES MOVE WEST TO EAST FROM THE OHIO VALLEY INTO THE MID-
ATLANTIC, THIS WILL ALLOW FOR SOME ORGANIZATION INTO CLUSTERS
TRACKING PARALLEL TO THE FRONT (AND PRE-FRONTAL TROUGH). AHEAD OF
THE FRONT, THE CORFIDI VECTORS AND MEAN FLOW WILL ALIGN FROM THE
WEST, LEADING TO AN INCREASED BACKBUILDING POTENTIAL INTO THE
HIGHER THERMODYNAMICS WITH CELLS THEN TRACKING ACROSS THE SAME
AREAS OF THE MID-ATLANTIC STATES AND INTO SOUTHERN NEW ENGLAND.
THIS WILL OCCUR AHEAD OF THE FRONT WHICH WILL PRODUCE A SECOND
ROUND OF HEAVY RAINFALL POTENTIAL, ALBEIT WITH MORE PROGRESSIVE NW
TO SE MOTION TO THE CELLS.
THE INHERITED SLGT RISK HAS BEEN ADJUSTED TO ACCOUNT FOR NEW
GUIDANCE, AND DUE TO ELEVATED PROBABILITIES FROM BOTH THE HREF AND
REFS (40-60% FOR 3"/24HRS, 10-15% FOR 5"/24HRS) ATOP SENSITIVE
AREAS DUE TO URBAN DEVELOPMENT AND RECENT RAINFALL PRODUCING COMPROMISED
FFG. THIS INCLUDED CONNECTING THE SLGT RISKS ACROSS PA WHERE THE
ARW GUIDANCE IS MOST AGGRESSIVE AND THERE IS SUFFICIENT POTENTIAL
FOR SOME TRAINING (OR MESO-CYCLONES TO ENHANCE RAINFALL RATES) TO
INCLUDE A LARGER AREA. CONSIDERED AN ELEVATED INTERNAL SLGT RISK
FOR THE TRI-STATE AREA AS WELL, BUT ENOUGH UNCERTAINTY IN POSITION
AND TIMING OF REDEVELOPMENT AFTER CAPE EXHAUSTION THIS MORNING
PREVENTED THAT CATEGORY INCREASE.
..FLORIDA PANHANDLE THROUGH SOUTHWEST GEORGIA
DEEP MOISTURE SPREADING NORTH AHEAD OF A SLOW-MOVING MID-TO-UPPER
LEVEL LOW WILL POOL ALONG A SURFACE TROUGH EXTENDING OUT OF THE
EASTERN GULF. THIS MOISTURE (PWS INCREASING TO ABOVE 2 INCHES)
WILL FUEL SLOW-MOVING STORMS AS CORFIDI VECTORS BECOME ALIGNED
ANTI-PARALLEL TO WEAK 0-6KM MEAN WINDS OF JUST 5-10 KTS. WITH RAIN
RATES POSSIBLY (20-40%) EXCEEDING 2"/HR AT TIMES THIS COULD CREATE
AT LEAST ISOLATED INSTANCES OF EXCESSIVE RAINFALL LEADING TO FLASH
FLOODING.
..WESTERN FLORIDA PENINSULA
A CONVECTIVE MCV POSITIONED WEST OF THE FLORIDA PANHANDLE ACROSS
THE NORTHEAST GULF WILL DRIFT WESTWARD TODAY WITHIN A POOL OF
TROPICAL PWS NEARING 2.25 INCHES. AS THIS FEATURE DRIFTS SLOWLY
WESTWARD, IT HAS, AT LEAST THIS MORNING, TEMPORARILY STALLED INFLOW
ALONG THE FLORIDA WEST COAST BETWEEN NAPLES AND FORT MEYERS. THE
HIGH-RES CAMS ARE NOT EXTREMELY AGGRESSIVE WITH RAINFALL TODAY,
BUT HAVE BEEN UNDER-FORECASTING THE CURRENT ACTIVITY (MRMS ALREADY
2-4" IN SOME AREAS WITH HOURLY RAIN RATES OF 2-3"). IF THIS BAND
CONTINUES TO STALL, CONTINUED IMPRESSIVE RAINFALL RATES ARE LIKELY,
AND THE RECENT RRFS, HRRR, AND SOME OF THE EXPERIMENTAL REFS
MEMBERS SHOW AN ADDITIONAL 2-4" OF RAIN ARE POSSIBLE. THIS HAS
RESULTED IN A NARROW MRGL RISK ADDITION WHICH ALIGNS WELL WITH
RECENTLY ISSUED MPD #764.
WEISS
DAY 2
VALID 12Z SUN JUL 19 2026 - 12Z MON JUL 20 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS THE
SOUTHWESTERN U.S. FROM WEST TEXAS TO SOUTHERN UTAH, AS WELL AS
PORTIONS OF NORTH CAROLINA...
..SOUTHWESTERN U.S.
THE MONSOON RIDGE WILL PERSIST IN A FAVORABLE ALIGNMENT SUNDAY,
KEEPING THE OVERALL SYNOPTIC PATTERN RELATIVELY UNCHANGED FROM D1.
THIS WILL CREATE ANOTHER DAY OF SCATTERED TO WIDESPREAD CONVECTION
FROM THE DESERT SOUTHWEST, THROUGH WEST TEXAS, AND NORTHWARD INTO
THE GREAT BASIN AND INTERMOUNTAIN WEST. THE PRIMARY DIFFERENT
BETWEEN THE SYNOPTIC PATTERN SATURDAY VS SUNDAY MAY BE JUST A
SUBTLE REORGANIZATION OF THE RIDGE CENTER NEAR THE WY/CO BORDER,
WHICH COULD ALLOW FOR A SUBTLY FARTHER NW SHIFT OF THUNDERSTORM
ACTIVITY THAN WHAT OCCURS SATURDAY.
REGARDLESS, THE ENVIRONMENT WILL SUPPORT ANOTHER ACTIVE DAY, AND
WITH PWS REACHING +2 TO +3 SIGMA (A PLUME OF 0.75" NORTH TO 1.75"
SOUTH) OVERLAPPING WIDESPREAD MUCAPE OF 250-1000 J/KG, THIS WILL
SUPPORT HEAVY RAINFALL RATES WITHIN ANY OF THE CONVECTION ON
SUNDAY. HREF AND REFS NEIGHBORHOOD PROBABILITIES INDICATE A 60-80%
CHANCE OF HOURLY RAINFALL TO 1", WITH LOCALLY 2"/HR RATES ALSO
POSSIBLE (10-20%). ALTHOUGH BULK SHEAR IS EXPECTED TO REMAIN
MODEST, UP TO 20 KTS, SUGGESTING PRIMARILY PULSE TYPE CONVECTION,
WEAK 0-6KM MEAN WINDS AND CORFIDI VECTORS WILL ALLOW FOR STORM
MERGERS AND BOUNDARY INTERACTIONS TO CAUSE CHAOTIC AND SLOW
MOTIONS, WITH SUBTLE TERRAIN TYING OR BOUNDARY STALLING STORMS
DEVELOPING AT TIMES. THIS WILL CREATE LOCALLY 3-4" OF RAIN,
ESPECIALLY FROM THE MOGOLLON RIM SOUTHEAST INTO WEST TEXAS WHERE
HIGHER MUCAPE IS PROGGED. HOWEVER, ANYWHERE THESE SLOW STORMS
DEVELOP WITH THE INTENSE RAIN RATES, INSTANCES OF FLASH FLOODING
WILL BE POSSIBLE, ESPECIALLY ATOP SENSITIVE TERRAIN FEATURES LIKE
SLOT CANYONS AND DRY WASHES, OR OVER BURN SCARS AND URBAN AREAS.
ONCE AGAIN, THE PROBABILITIES INDICATE THE HEAVIEST RAINFALL WILL
OCCUR IN THE HIGHER TERRAIN, BUT LIGHT E/NE FLOW AND OUTFLOWS COULD
HELP STORMS DIVE OFF THE TERRAIN INTO THE LOWER DESERTS AT TIMES AS
WELL.
..MID-MISSISSIPPI VALLEY THROUGH THE CAROLINAS
AFTER COORDINATION WITH THE EASTERN NC WFOS, A TARGETED SLGT RISK
HAS BEEN ADDED FOR EASTERN NC EMBEDDED WITHIN THE BROADER MRGL
EXTENDING FROM THE MID-MISSISSIPPI VALLEY THROUGH THE TENNESSEE
VALLEY AND INTO THE SOUTHERN MID-ATLANIC STATES. THIS AREA WILL SEE
SCATTERED TO WIDESPREAD THUNDERSTORM DEVELOPMENT ALONG AND AHEAD OF
A COLD FRONT WHICH WILL SLOWLY DROP SOUTHWARD THROUGH THE DAY. THE
DOWNSTREAM ENVIRONMENT WILL BE EXTREMELY SUPPORTIVE OF HEAVY RAIN
THANKS TO PWS OF 2-2.25 INCHES OVERLAPPED WITH MUCAPE ABOVE 2000
J/KG.
WHILE MUCH OF THE CONVECTION WILL BE OF THE PULSE VARIETY, SOME
INCREASING BULK SHEAR REACHING 25-35 KTS, ESPECIALLY LATE ACROSS NC
AND THE MID-MISSISSIPPI VALLEY COULD HELP ORGANIZE STORMS INTO
CLUSTERS, WHICH WILL THEN MOVE PARALLEL TO THE BOUNDARY TO SUPPORT
PROLONGED PERIODS OF TRAINING. WITH RAINFALL RATES OF 2"/HR OR
MORE, THIS COULD CAUSE LOCALLY MORE THAN 3" OF RAIN, WITH A 20-40%
CHANCE OF AT LEAST 5" ACROSS EASTERN NC WHERE A SHORTWAVE WILL HELP
SPAWN A WAVE OF LOW PRESSURE TO IMPROVE ASCENT AND ORGANIZE
THUNDERSTORM ACTIVITY.
..EASTERN GULF COAST
A TROPICAL DISTURBANCE (AL91) FOR WHICH NHC HAS A 40% OF
DEVELOPMENT OVER THE NEXT 7 DAYS IN THE NORTHEASTERN GULF WILL
SPREAD AT LEAST MODERATE RAINFALL ONSHORE THE WEST COAST OF FLORIDA
THROUGH THE PANHANDLE AND POTENTIALLY AS FAR EAST AS EASTERN
LOUISIANA. WHILE THERE IS CONSIDERABLE UNCERTAINTY INTO THE ONSHORE
EXTENT OF QPF ON D2, THE HREF AND REFS BOTH SUGGEST A 20-40% CHANCE
OF AT LEAST 3" OF RAINFALL ALONG THE COAST, DRIVING THE ADJUSTMENTS
TO THE INHERITED MRGL RISK.
..UPPER MISSISSIPPI VALLEY
A SHORTWAVE EMBEDDED WITHIN SQUEEZED MID-LEVEL FLOW WILL CREST THE
FOUR-CORNERS RIDGE AND THEN DIVE SOUTHEAST SUNDAY EVENING/NIGHT
INTO THE NORTHERN PLAINS AND UPPER MIDWEST. THIS SHORTWAVE WILL
INTERACT WITH A FRONTAL SYSTEM TO ENHANCE ASCENT, WITH A WAVE OF
LOW PRESSURE POTENTIALLY ALSO DEVELOPING. AS THE LLJ DEVELOPS
WITHIN THE ACCOMPANYING WARM SECTOR, IT IS PROGGED TO ACCELERATE TO
25-35 KTS, DRAWING ROBUST THERMODYNAMICS (PWS ABOVE 2" WITH MUCAPE
OVER 3000 J/KG) NORTHWARD AND ISENTROPICALLY ASCENDING THE NW TO SE
ORIENTED WARM FRONT. THIS WILL HELP SPAWN THUNDERSTORMS DURING THE
EVENING, WITH BACKBUILDING/TRAINING POSSIBLE FROM THE EASTERN
DAKOTAS INTO SOUTHERN MINNESOTA. THE HREF AND REFS PROBABILITIES
SUGGEST A 15-25% CHANCE FOR AT LEAST 3" OF RAINFALL THANKS TO
TRAINING 1-2"/HR RAIN RATES, SO A MRGL RISK WAS ADDED FOR AT LEAST
LOCALIZED FLASH FLOOD POTENTIAL.
WEISS
DAY 3
VALID 12Z MON JUL 20 2026 - 12Z TUE JUL 21 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
ARIZONA AND NEW MEXICO...
..SOUTHWEST
CHANGES FROM INHERITED WERE PRIMARILY COSMETIC TO ACCOUNT FOR NEW
GUIDANCE, BUT ANOTHER DAY OF ACTIVE (ALTHOUGH WITH SOMEWHAT LESS
COVERAGE THAN THE WEEKEND) MONSOONAL CONVECTION IS EXPECTED. THIS
IS DUE TO A GENERALLY UNCHANGED SYNOPTIC PATTERN WITH ANOMALOUS
MOISTURE SUPPORTING CONVECTIVE ACTIVITY AND RAINFALL EFFICIENCY.
SOUTH OF THE RIDGE, AS IN THE PREVIOUS FEW DAYS, SHORTWAVES
ROTATING WESTWARD WILL HELP STEER AND ENHANCE CONVECTIVE COVERAGE,
AND WHERE THIS OVERLAPS WITH THE GREATEST INSTABILITY/PW ACROSS
NM/AZ SHOULD RECEIVE THE GREATEST COVERAGE OF THUNDERSTORMS WITH
FLASH FLOOD POTENTIAL. THERE IS SOME CONCERN THAT INSTABILITY MAY
STRUGGLE TO RETURN MONDAY DUE TO WIDESPREAD CONVECTIVE COVERAGE AND
RESIDUAL CLOUD COVER SUNDAY NIGHT, WHICH MAY NECESSITATE
ADDITIONAL ADJUSTMENTS TO THE RISK AREA, BUT AT THIS TIME IT STILL
APPEARS THERE WILL BE ANOTHER DAY OF SCATTERED TO WIDESPREAD
CONVECTION WITH AT LEAST SCATTERED FLASH FLOOD INSTANCES. THIS WILL
BE MOST LIKELY ACROSS VULNERABLE FEATURES SUCH AS DRY WASHES, BURN
SCARS, AND SLOT CANYONS.
..GREAT LAKES
A WELL-DEFINED SHORTWAVE INTERACTING WITH DEEPENING MOISTURE IS
EXPECTED TO PRODUCE STRONG STORMS CAPABLE OF PRODUCING HEAVY
RAINFALL ACROSS THE REGION. LOCALLY BACKED AND ACCELERATED LOW-
LEVEL FLOW WILL HELP SURGE PWS TO 2 INCHES OR MORE, ESPECIALLY
WITHIN A PROGRESSIVE WARM SECTOR PROGGED TO RACE ACROSS THE REGION
DURING D3. THIS MOISTURE, ALONG WITH STRONG ASCENT DRIVEN BOTH BY
LOW-LEVEL ISENTROPIC ASCENT AND FAVORABLE UPPER JET DYNAMICS, WILL
FUEL THE POTENTIAL FOR HEAVY RAINFALL-PRODUCING STORMS. INCREASING
BULK SHEAR TO 30-50 KTS WILL HELP ORGANIZE CONVECTION INTO CLUSTERS
OR SUPERCELLS, RAISING THE POTENTIAL FOR INTENSE RAIN RATES OF
1-2"/HR, THROUGH WHICH ANY SHORT-TERM TRAINING COULD ENHANCE THE
FLOOD RISK. AT THIS TIME STORMS MAY MOVE RAPIDLY ENOUGH TO PRECLUDE
A HIGHER RISK, BUT WILL CONTINUE TO MONITOR FOR A POSSIBLE TARGETED
UPGRADE TO A SLGT RISK WITH LATER ISSUANCES.
..NORTH CAROLINA/SOUTHERN VIRGINIA
A MARGINAL RISK WAS MAINTAINED WHERE A FRONT AND COINCIDING POOL
OF DEEP MOISTURE (PWS AT OR ABOVE 2 INCHES) ARE EXPECTED TO LINGER,
EXTENDING THE THREAT FOR HEAVY RAINFALL AND POSSIBLE FLASH
FLOODING INTO A SECOND DAY. THERE IS SOME POTENTIAL A SLGT RISK MAY
BE NEEDED HERE AS WELL, BUT THAT RISK WILL BE SOMEWHAT DEPENDENT ON
WHAT OCCURS D2, SO AFTER COORDINATION WITH THE WFOS, OPTED TO
MAINTAIN THE MRGL FOR NOW AND REASSESS AS THE EVENT GETS CLOSER.
..FLORIDA GULF COAST
CONSIDERABLE UNCERTAINTY REMAINS REGARDING AL91 IN THE NORTHERN
GULF. THERE WILL CONTINUE TO BE AT LEAST A LOW-END RISK FOR HEAVY
RAINFALL AROUND THIS SYSTEM AS TROPICAL MOISTURE STREAMS NORTHWARD
TO THE FL PANHANDLE AND SURROUNDING AREAS. AT THIS TIME THE MRGL
RISK WAS MAINTAINED AND ONLY COSMETICALLY ADJUSTED, BUT FUTURE
REFINEMENTS ARE EXPECTED AS THIS SYSTEM BECOMES MORE ORGANIZED.
WEISS
DAY 4 AND DAY 5
VALID 12Z TUE JUL 21 2026 - 12Z THU JUL 23 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHWEST AS WELL AS THE CENTRAL APPALACHIANS ON TUESDAY...
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR EASTERN NORTH
CAROLINA AND SOUTHEASTERN VIRGINIA ON WEDNESDAY...
2030Z DISCUSSION...
FEW CHANGES NEEDED TO EITHER THE EXCESSIVE RISK IN THE EASTERN US
OR THE WESTERN STATES. THE 12Z MODEL QPF AND THE ENSEMBLE GUIDANCE
STILL ALIGNED FAIRLY CLOSELY WITH PREVIOUS RUNS...SO CHANGES TO THE
DAY 4/5 ERO WERE MINOR ADJUSTMENTS RATHER THAN A SHIFT IN THE
OVERALL FORECAST REASONING,
BANN
PREVIOUS DISCUSSION...
..SOUTHWEST
THE SOUTHWEST MONSOON WILL REMAIN IN FULL FORCE ACROSS ARIZONA AND
INTO UTAH ON TUESDAY. MOISTURE ANOMALIES ESPECIALLY TO THE NORTH
ACROSS UTAH COULD APPROACH 5 SIGMA ABOVE NORMAL FOR THIS TIME OF
YEAR, WHILE INTO ARIZONA, PWATS TO 2 INCHES WILL BE A SOLID 3 SIGMA
ABOVE NORMAL. WITH DAYTIME HEATING, RENEWED ROUNDS OF THUNDERSTORMS
ARE EXPECTED TO REDEVELOP FOR THE LATEST IN THE MULTI-AFTERNOON
PATTERN. SOIL MOISTURE LEVELS ARE ALREADY SATURATED OVER MUCH OF
ARIZONA AND INTO SOUTHERN UTAH. EXPECT WITH THE THERMAL LOW PEAKING
IN INTENSITY ON TUESDAY, THAT FLASH FLOODING CONCERNS WILL BECOME
MORE WIDESPREAD AS RAINS IMPACT BEYOND THE 4 CORNERS INTO NEVADA,
IDAHO, AND WYOMING. A SLIGHT RISK UPGRADE WAS INTRODUCED WITH THIS
UPDATE, AND IT'S POSSIBLE LOCALIZED AREAS MAY SEE FURTHER UPGRADES
AS TUESDAY APPROACHES. BY WEDNESDAY, RIDGING OVER THE SOUTHWEST
WILL PUSH THE GREATER THREATS FOR THUNDERSTORMS FURTHER NORTH INTO
THE INTERMOUNTAIN WEST, WITH A LOW DEVELOPING OVER THE PLAINS
ALLOWING FOR SOME OF THE MOISTURE TO OVERSPREAD INTO PORTIONS OF
THE CENTRAL PLAINS. THE SIGNAL FOR HEAVY RAIN LESSENS ON WEDNESDAY,
SO THE THREAT DROPS TO MARGINAL FOR NOW, THOUGH A SLIGHT MAY BE
NEEDED INTO THE INTERMOUNTAIN WEST WITH CONTINUED CONSISTENCY IN
THE GUIDANCE.
..CENTRAL APPALACHIANS
A SLIGHT RISK UPGRADE WAS ALSO INTRODUCED FOR PORTIONS OF THE
CENTRAL APPALACHIANS, PARTICULARLY ACROSS WEST VIRGINIA AND INTO
SOUTHWEST PENNSYLVANIA. ABUNDANT MOISTURE ACROSS THE MID-ATLANTIC
WILL INTERACT WITH A STRONG COLD FRONT PUSHING SOUTHWEST ACROSS
OHIO DURING THE AFTERNOON. THIS WILL ALLOW FOR NUMEROUS
THUNDERSTORMS TO DEVELOP TUESDAY AFTERNOON. UPSLOPE FLOW INTO THE
FLASH FLOOD PRONE MOUNTAINS OF WEST VIRGINIA AND PENNSYLVANIA WILL
SUPPORT ADDITIONAL THUNDERSTORM DEVELOPMENT AS COMPARED WITH AREAS
FURTHER WEST WHERE THE FRONT WILL CLEAR THE MOISTURE, AND FURTHER
EAST WHERE THERE WILL BE LESS FORCING. PWATS APPROACHING 2 INCHES
WILL ALSO SUPPORT STORMS CAPABLE OF MULTIPLE INCH PER HOUR RAINFALL
RATES, ESPECIALLY AS THEY RUN INTO THE MOUNTAINS.
TO THE EAST ACROSS THE MID-ATLANTIC, MOISTURE LEVELS FURTHER
INCREASE, WITH SOME AREAS PERHAPS REACHING 2.25 INCH PWATS TUESDAY
AFTERNOON. THE FORCING WILL BE A BIT MORE UNCERTAIN, BUT ANY STORMS
THAT FORM WILL BE CAPABLE OF VERY HEAVY RAINS. THE I-95 CORRIDOR
FROM DC TO NYC WILL HAVE TO BE CLOSELY MONITORED AS THESE HEAVILY
POPULATED AND FLOOD PRONE AREAS MAY HAVE ENOUGH WIDESPREAD ACTIVITY
TO NEED FURTHER UPGRADES.
..TIDEWATER OF NORTH CAROLINA AND VIRGINIA
ON DAY 5/WEDNESDAY, THE SAME COLD FRONT THAT SWINGS THROUGH THE
MIDWEST, NORTHEAST, AND MID-ATLANTIC ON TUESDAY SLOWS DOWN ITS
FORWARD SPEED, PERHAPS EVEN STALLING TO THE WEST OF THE TIDEWATER
OF NORTH CAROLINA AND VIRGINIA. PLENTIFUL TROPICAL MOISTURE
CONTINUES RIDING NORTHEASTWARD ALONG THAT FRONT, PROVIDING AMPLE
OPPORTUNITY FOR NUMEROUS TRAINING SHOWERS AND THUNDERSTORMS TO
DEVELOP OVER THE REGION, LIKELY MOVING OUT OVER THE ATLANTIC OFF
OCEAN CITY, MARYLAND AND POINTS NORTH. THUS, THE FOCUS WILL BE IN
THE HIGHLY URBANIZED HAMPTON ROADS AREA, EXTENDING INTO MUCH OF THE
COASTAL PLAIN OF NORTH CAROLINA. GIVEN THE PRETTY IMPRESSIVE SIGNAL
FOR HEAVY RAIN, HAVE STARTED OUT THE DAY 5 ERO WITH A SLIGHT RISK
IN THIS REGION. THERE REMAINS SOME UNCERTAINTY AS TO WHETHER ANY
TROPICAL DEVELOPMENT OVER THE NORTHEASTERN GULF CONTRIBUTES TO THE
HEAVY RAINFALL EXPECTED IN THIS REGION ON WEDNESDAY. GIVEN THE
SIGNALS FOR HEAVY RAIN EXPECTED SUNDAY/MONDAY OVER EASTERN NORTH
CAROLINA, EXPECT THE SOILS BY WEDNESDAY TO BE SIGNIFICANTLY MORE
SATURATED THAN THEY ARE NOW, CONTRIBUTING TO THE HEIGHTENED FLASH
FLOODING RISK.
WEGMAN
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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