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FOUS30 KWBC 271955
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
355 PM EDT MON JUL 27 2026
DAY 1
VALID 1832Z MON JUL 27 2026 - 12Z TUE JUL 28 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN EFFECT FOR PARTS
OF SOUTHEAST WISCONSIN, NORTHEAST/EAST-CENTRAL ILLINOIS, AND
NORTHWEST/WEST-CENTRAL INDIANA...
1830Z SPECIAL UPDATE...
A SLGT RISK WAS ADDED TO PARTS OF THE MIDWEST FROM SE WI THROUGH
MUCH OF NE IL AND NW IN, INCLUDING THE CHICAGO, INDIANAPOLIS, AND
MILWAUKEE METRO REGIONS. THIS IS DUE TO ONGOING HEAVY RAINFALL AND
THE EXPECTATION FOR INTENSE RAINFALL RATES TO CONTINUE FOR SEVERAL
HOURS WHILE THE THREAT SLIDES SOUTHWARD WITH TIME. BOTH 17Z RUNS
OF THE HRRR AND RRFS SUPPORT 2-5" ADDITIONAL RAINFALL AMOUNTS
THROUGH 06Z, WHICH WOULD PRODUCE SCATTERED AREAS OF FLASH FLOODING.
URBAN LOCATIONS COULD SEE SIGNIFICANT STREET FLOODING SHOULD
THUNDERSTORMS TRAIN OVER THE REGION. AS THE COMPLEX PUSHES
SOUTHWARD THIS EVENING AND OVERNIGHT ACROSS CENTRAL AND SOUTHERN
IL/IN, RAINFALL RATES AND THE THREAT OF BACKBUILDING STORMS SHOULD
DIMINISH AS BETTER FORCING SHIFTS EASTWARD INTO THE UPPER OHIO
VALLEY. SEE MPD 0861 FOR MORE INFORMATION.
SNELL
PREVIOUS DISCUSSION...
..FOUR CORNERS STATES ONTO THE CENTRAL PLAINS
THE MONSOON RIDGE GETS SLIGHTLY SUPPRESSED SOUTH TODAY BY
SHORTWAVES CRESTING ITS PERIPHERY OVER THE NORTHERN ROCKIES. THIS
WILL SQUELCH THE HIGHER PW A BIT SOUTH FROM PREVIOUS DAYS, BUT
OTHERWISE THE RIDGE REMAINS IN PLACE WITH WEAK IMPULSES ROTATING
AROUND IT TO ENHANCE ASCENT AND RESULTING CONVECTION. ONCE AGAIN,
THE FOCUS FOR THUNDERSTORM DEVELOPMENT WILL BE ACROSS THE HIGHER
TERRAIN LATE THIS MORNING, BEFORE EXPANDING ACROSS THE FOUR CORNERS
STATES, WITH SOME ORGANIZATION POSSIBLE THROUGH 20-30 KTS OF BULK
SHEAR. WHILE PWS WILL STILL BE +1 TO +2 SIGMA FROM AZ THROUGH WY,
THE MOST IMPRESSIVE CAPE (APPROACHING 750 J/KG) LOOK TO BE CONFINED
TO AZ/NM, WHICH CAN BE A BETTER DISCRIMINATOR FOR EXCESSIVE
RAINFALL POTENTIAL WITHIN THE MONSOON. HOWEVER, ANY CONVECTION HAS
THE POTENTIAL TO PRODUCE INTENSE RAIN RATES LEADING TO HOURLY
RAINFALL OF 1-1.5", WHICH COULD PRODUCE AT LEAST ISOLATED FLASH
FLOOD RESPONSES OVER VULNERABLE TERRAIN FEATURES OR BURN SCARS.
STORMS THAT DEVELOP ACROSS UT/WY/CO MAY FEATURE FASTER FORWARD
PROPAGATION (AFTER BRIEF SLOW DOWNS DURING INITIATION) SO THE MRGL
RISK WAS EXPANDED SLIGHTLY INTO THE CENTRAL PLAINS. HOWEVER, THIS
FASTER MOTION SHOULD AT LEAST SOMEWHAT LIMIT THE RUNOFF POTENTIAL.
FARTHER SOUTH INTO AZ A SHORTWAVE MOVING ALONG THE MEXICO/ARIZONA
BORDER WITHIN THE ELEVATED SHEAR MAY HELP ORGANIZED CLUSTERS OF
STORMS MOVING MORE SLOWLY WESTWARD, AND THIS IS REFLECTED BY
ELEVATED (BUT STILL MODEST) PROBABILITIES FOR 3" OF RAIN TODAY.
CONSIDERED A TARGETED SLGT RISK FOR THE TWC CWA BUT SIMULATED
REFLECTIVITY FROM THE CAMS AND THE UA WRF WERE NOT SUFFICIENT FOR
AN UPGRADE AT THIS TIME.
..GREAT LAKES AND OHIO VALLEY INTO THE NORTHEAST US
A POTENT SHORTWAVE DIVING OUT OF ONTARIO ACROSS THE GREAT LAKES
WILL INTERACT WITH A COMPLEX SURFACE PATTERN OVER THE REGION TO
DRIVE SCATTERED TO WIDESPREAD THUNDERSTORMS THROUGH THE DAY.
ACTIVITY THIS MORNING IS ALREADY PRODUCING HEAVY RAINFALL RATES
MEASURED VIA MRMS OF OVER 1"/HR WITHIN THE PRONOUNCED ASCENT AS IT
IMPINGES UPON AN IMPRESSIVE OVERLAP OF PW/CAPE MEASURED VIA MORNING
12Z SOUNDINGS AT APX/GRB OF NEAR RECORD VALUES (1.7-2.1 PWS AND
4000-5000 J/KG CAPE). AS THE AFTN PROGRESSES, CONVECTION WILL
BECOME INCREASINGLY WIDESPREAD AS THE SHORTWAVE DIVES SOUTH AND
PUSHES A COLD FRONT (AND ACCOMPANYING WAVE OF LOW PRESSURE) THROUGH
THE GREAT LAKES AND SOUTHEAST TOWARDS THE OHIO VALLEY/CENTRAL
APPALACHIANS). WHILE THE THERMODYNAMIC ENVIRONMENT WILL SUPPORT
INTENSE RAIN RATES WITHIN ANY THUNDERSTORMS TODAY, AND 40-50KTS OF
BULK SHEAR WILL HELP ORGANIZE STORMS INTO CLUSTERS AND/OR
SUPERCELLS, MEAN WINDS OF 30-40 KTS SUGGEST CONVECTION WILL REMAIN
PROGRESSIVE, AND CORFIDI VECTORS DO NOT SUPPORT MUCH
BACKBUILDING/TRAINING. SO WHILE LOCAL IMPACTS DUE TO FLASH FLOODING
ARE POSSIBLE, THE OVERALL RISK MATCHES BEST THE MRGL RISK CATEGORY
SO THE INHERITED WAS CHANGED ONLY COSMETICALLY FOR NEW GUIDANCE.
..WESTERN FLORIDA PENINSULA
WEAK SHORTWAVE DIVING ALONG OR JUST WEST OF THE FLORIDA PENINSULA
WILL WORK TOGETHER WITH BROAD DIRECTIONAL JET- LEVEL DIFFLUENCE TO
SPAWN REPEATED ROUNDS OF THUNDERSTORM ACTIVITY TODAY. THIS
CONVECTION WILL OCCUR WITHIN ROBUST PW ANOMALIES REACHING +1.5 TO
+2.0 SIGMA FOR THE SOUTHERN HALF OF FLORIDA, WHICH WHEN COMBINED
WITH SBCAPE EXCEEDING 3000 J/KG WILL SUPPORT TORRENTIAL RAIN RATES.
WHILE SHEAR WILL BE MINIMAL INDICATING PULSE-TYPE CONVECTION, WEAK
FLOW AND RESULTING CELL COLLISIONS OR OUTFLOW MERGERS, AS WELL AS
THE GULF BREEZE, WILL SUPPORT SCATTERED TO WIDESPREAD
THUNDERSTORMS, ALL OF WHICH MAY CONTAIN 2-3"/HR RAINFALL. DUE TO
THE NATURE OF THIS CONVECTION, PLACING THE AXIS OF HEAVIEST AMOUNTS
REMAINS UNCERTAIN, BUT THERE IS A COMMON SIGNAL IN BOTH REFS AND
HREF PROBABILITIES FOR LOCALLY MORE THAN 5" (20-40% CHANCE) NEAR
TAMPA BAY, SO THE INHERITED MRGL RISK WAS CONTINUED FOR THIS AREA,
BUT EXPANDED ALONG THE COAST FOR POTENTIAL BENEATH THE FORCING
CREATED BY THE UPPER DIFFLUENCE, AND ADDED THE FLORIDA KEYS AFTER
COORDINATION WITH WFO KEY.
..COASTAL MID-ATLANTIC
A SURFACE TROUGH WILL SHARPEN EAST OF I-95 THIS AFTN PROVIDING A
FOCUS FOR ASCENT AND CONVECTIVE DEVELOPMENT. THE HIGH-RES CAMS
SUGGEST DEVELOPMENT WILL GENERALLY BE ISOLATED, BUT WITHIN
FAVORABLE THERMODYNAMICS CHARACTERIZED BY PWS ABOVE 1.5 INCHES AND
SBCAPE OF 2000 J/KG OR MORE. THIS WILL SUPPORT INTENSE RAIN RATES
WITHIN ANY STORMS THAT DEVELOP, AND BOTH THE REFS AND HREF
NEIGHBORHOOD PROBABILITIES REACH 50-70% FOR HOURLY RAINFALL OF 1
INCH OR MORE. WHILE THERE IS SOME UNCERTAINTY INTO THE COVERAGE AND
PLACEMENT OF ACTIVITY THIS AFTN, THE INHERITED MRGL RISK WAS
CONTINUED WITH JUST SUBTLE COSMETIC MODIFICATIONS SINCE SOILS ARE
SATURATED FROM HEAVY ANTECEDENT RAINFALL.
WEISS
DAY 2
VALID 12Z TUE JUL 28 2026 - 12Z WED JUL 29 2026
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR THE TRI-STATE
AREA OF NEW JERSEY, NEW YORK, AND CONNECTICUT...
..SOUTHERN APPALACHIANS THROUGH NEW ENGLAND
AN ANOMALOUSLY STRONG UPPER LOW WILL PRODUCE IMPRESSIVE DYNAMICS TO
CREATE THE POTENTIAL FOR SIGNIFICANT FLASH FLOODING ACROSS THE
TRI-STATE AREA ON TUESDAY.
A SHORTWAVE MOVING ACROSS THE GREAT LAKES TODAY WILL DEEPEN INTO A
CLOSED LOW OVER UPSTATE NY TUESDAY EVENING, AND THEN AMPLIFY AS IT
CURLS SOUTHEAST INTO NEW ENGLAND. NAEFS 500-850MB HEIGHTS FALL TO
BELOW THE 1ST PERCENTILE (OR EVEN BELOW THE MINIMUM CLIMATOLOGY)
ACCORDING TO NAEFS BY 00Z WEDNESDAY. THIS INTENSE SYSTEM WILL HELP
DRIVE INCREASING DIVERGENCE DOWNSTREAM, WHICH WHEN COMBINED WITH
THE ACCOMPANYING HEIGHT FALLS WILL RESULT IN BROAD DEEP LAYER
ASCENT FROM THE MID-ATLANTIC INTO NEW ENGLAND. AT THE SAME TIME,
THE DEEPENING SYSTEM WILL FORCE ACCELERATION OF THE 850MB INFLOW,
REFLECTED BY NAEFS PERCENTILES IN THE 850MB WIND TO ABOVE THE 99TH
PERCENTILE, FORCING ROBUST MOISTURE CONVERGENCE INTO THE MID-
ATLANTIC AND NORTHEAST.
AS IS TYPICAL FOR LATE JULY, PWS AND SBCAPE WILL BE NEAR
CLIMATOLOGICAL MAXIMUMS (REFLECTED VIA THE SPC SOUNDING
CLIMATOLOGY), AND THIS EVENT WILL BE NO DIFFERENT AS PWS ARE
PROGGED TO BE AROUND 1.75 INCHES OVERLAPPING MUCAPE OF 2000-3000
J/KG. STRONG ASCENT IN THE VICINITY OF THIS ANOMALOUS CLOSED LOW
AND NEAR THE ACCOMPANYING OCCLUDED SURFACE LOW INTO THESE STRONG
THERMODYNAMICS SETS A SITUATION FAVORABLE FOR HEAVY, TRAINING
RAINFALL, AND FLASH FLOODING.
BOTH HREF AND REFS PROBABILITIES FOR 2"/HR RAINFALL REACH 15-25%,
AND CORFIDI VECTORS ALIGNED ANTI- PARALLEL TO THE MEAN WIND WHICH
WILL BE ALIGNED TO THE APPROACHING FRONT, SUGGESTS A STRONG
BACKBUILDING AND TRAINING POTENTIAL. WHILE THERE IS STILL QUITE A
BIT OF TIMING SPREAD AMONG THE VARIOUS CAMS AS TO WHEN THE
STRONGEST CONVECTION WILL PIVOT THROUGH, THE EXCEEDANCE
PROBABILITIES FOR BOTH 5"/24HRS AND 8"/24HRS ARE IMPRESSIVE (40-70%
AND 10-30%, RESPECTIVELY) DESPITE SOME UNCERTAINTY IN POSITION.
THIS COMBINED WITH THE 100-YR RI EXCEEDANCES EXCEEDING 20% INDICATE
INCREASING CONFIDENCE FOR WIDESPREAD FLASH FLOODING WITH LOCALLY
SIGNIFICANT EVENTS POSSIBLE. AFTER COORDINATION WITH THE AFFECTED
WFOS, A MDT RISK HAS BEEN INTRODUCED, FOCUSED IN THE TRI-STATE
REGION WHERE FFG IS ALREADY MORE VULNERABLE DUE TO RECENT RAIN AND
THE GENERAL URBAN CORRIDOR.
DESPITE THE MDT RISK IN PLACE FOR THE TRI-STATE AREA, IT SHOULD BE
NOTED THAT THE REFS PROBABILITIES ARE A BIT DISPLACED SOUTH FROM
THE HREF, AND FOCUS THE HEAVIEST RAINFALL CLOSER TO PHILADELPHIA.
THE SURROUNDING SLGT RISK HAS BEEN EXPANDED TO ACCOUNT FOR THIS
POTENTIAL, AND THERE IS POTENTIAL FOR ADDITIONAL ADJUSTMENTS TO THE
HIGHER-END RISK AREAS IN PLACE FOR TUESDAY/TUESDAY NIGHT.
..FOUR CORNERS STATES ACROSS THE CENTRAL PLAINS
THE EXPANSIVE MONSOON RIDGE WILL BECOME ADDITIONALLY SQUEEZED TUESDAY
AS SHORTWAVES ROTATE ANTI-CYCLONICALLY AROUND IT BOTH TO THE NORTH
AND SOUTH. THIS WILL AGAIN SUPPORT AT LEAST SCATTERED MONSOON
CONVECTION AS PWS ABOVE 1 INCH RISE NORTHWARD INTO THE FOUR CORNERS
OVERLAPPED WITH SUFFICIENT INSTABILITY FOR AFTERNOON DEVELOPMENT.
ONCE AGAIN THE RISK WILL LIKELY INITIATE IN THE HIGHER TERRAIN
DURING THE ONSET OF PEAK HEATING, AND THEN THERE APPEARS TO BE
SUFFICIENT SHEAR (20-30 KTS) FOR SOME ORGANIZATION OFF THE TERRAIN
AND INTO THE LOWER ELEVATIONS, PRIMARILY IN NM AND CO.
STORM MOTIONS WILL AGAIN BE WEAK AS REFLECTED BY 0-6KM MEAN WINDS
OF JUST 5-10 KTS, AND LOCALLY CHAOTIC MOTION IS LIKELY WHERE
STORM CLUSTERS INTERACT WITH OTHER BOUNDARIES OR
MERGERS/COLLISIONS. THE CAMS, AS WELL AS HREF/REFS PMM SUGGEST A
LOCAL ENHANCEMENT TO QPF FROM FAR SOUTHEAST ARIZONA THROUGH WESTERN
NEW MEXICO AND INTO EASTERN COLORADO, WHICH IS WHERE MULTIPLE
ROUNDS OF STORMS ARE MORE LIKELY. AFTER COORDINATION WITH THE
AFFECTED WFOS, A SLGT RISK WAS INTRODUCED FOR THIS AXIS WHERE A
GREATER RISK FOR FLASH FLOODING EXISTS, ESPECIALLY ACROSS
VULNERABLE TERRAIN FEATURES.
..WESTERN FLORIDA PENINSULA AND THE KEYS
A SHORTWAVE DIVING ALONG THE FLORIDA PENINSULA/WESTERN GULF WILL
INTERACT WITH BROAD DIFFLUENCE ALOFT TO MAINTAIN DEEP LAYER ASCENT
FOR CONVECTION ACROSS THE EASTERN GULF AND INTO PARTS OF SOUTH
FLORIDA AND THE KEYS. MEAN 0-6KM WINDS OF JUST 5-10 KTS WILL BE
ALIGNED SW TO NW, ANTI- PARALLEL TO COLLAPSED CORFIDI VECTORS, AND
PARALLEL TO THE KEYS. THIS SUGGESTS THAT CONVECTION WILL REPEATEDLY
BUILD ACROSS THE GULF WHERE PWS WILL BE POOLED AT 2-2.25 INCHES
WITHIN IMPRESSIVE 2000-3000 J/KG MUCAPE. THIS WILL SUPPORT
WIDESPREAD ACTIVITY WHICH IS REFLECTED BY HIGH-RES CAM SIMULATED
REFLECTIVITY. WITHIN THESE IMPRESSIVE THERMODYNAMICS, RAINFALL
RATES OF 2-3"/HR ARE LIKELY AT TIMES, LEADING TO 2-4" OF RAINFALL
WITH LOCALLY HIGHER AMOUNTS. SOME OF THESE AREAS WILL BE SENSITIVE
FROM HEAVY RAIN ON D1, SO A MRGL RISK WAS ADDED FOR THE POTENTIAL
FOR ISOLATED IMPACTS ON TUESDAY.
..MISSOURI VALLEY
A WEAKENING BUT NOTABLE SHORTWAVE AND ACCOMPANYING VORTICITY
IMPULSE WILL CREST THE MONSOON RIDGE TO THE REST AND THEN RACE
STEADILY SOUTHEAST OVER THE CENTRAL PLAINS AND INTO THE MISSOURI
VALLEY BY TUESDAY NIGHT. THIS FEATURE WILL HELP PUSH A COLD FRONT
SOUTHWARD TOWARDS THE OZARKS, BUT BECOME ALIGNED PARALLEL TO THE
MID-LEVEL FLOW CAUSING IT TO STALL IN A NW TO SE ORIENTED FASHION.
AS THE SHORTWAVE MOVES ALONG THIS FRONT TUESDAY NIGHT IT WILL HELP
ACCELERATE THE ALREADY INTENSIFYING LLJ TO DRAW ROBUST
THERMODYNAMICS NORTHWARD. THIS WILL SUPPORT ORGANIZING CLUSTERS OF
CONVECTION OR AN MCS ALIGNING TO THE FRONT AS BOTH 0-6KM MEAN WINDS
AND CORFIDI VECTORS BECOME PARALLEL. WITH RAINFALL RATES LIKELY
REACHING 1-2"/HR AT TIMES, ANY TRAINING HAS THE POTENTIAL TO
PRODUCE 2-4" OF RAIN (HREF AND REFS PROBABILITIES FOR 3+" 20-25%)
LEADING TO INSTANCES OF FLASH FLOODING.
WEISS
DAY 3
VALID 12Z WED JUL 29 2026 - 12Z THU JUL 30 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE NORTHEAST...
..NORTHEAST
AN OCCLUDING SURFACE LOW BENEATH AN ANOMALOUS MID-LEVEL CLOSED LOW
WILL BRING HEAVY RAINFALL TO PARTS OF THE NORTHEAST AND NEW ENGLAND
ON WEDNESDAY. STRONG MID-LEVEL DIVERGENCE COMBINED WITH UPPER
DIFFLUENCE WILL PRODUCE DEEP LAYER ASCENT INTO ROBUST
THERMODYNAMICS CHARACTERIZED BY A PLUME OF 1.5 TO 1.7 INCH PWS AND
MUCAPE OF 500-750 J/KG. AT THE SAME TIME, THE DEEPENING SYSTEM WILL
ACCELERATE THE 850MB INFLOW TO 30-40 KTS, TAPPING ATLANTIC/GULF
STREAM MOISTURE TO FURTHER ENHANCE THE POTENTIAL FOR HEAVY RAIN.
THIS WILL SUPPORT AN EXPANSIVE AREA OF HEAVY RAINFALL FOR THE
NORTHEAST, WITH RAINFALL RATES OF 1"/HR OR MORE POSSIBLE AT TIMES,
LEADING TO WIDESPREAD 1-3" OF RAIN WITH LOCALLY HIGHER AMOUNTS
(SREF, GEFS, AND ECENS ALL HAVE AROUND A 10% CHANCE FOR 3+" OF
RAIN).
THERE WILL BE A SHARP GRADIENT OF INSTABILITY WHICH MAY
LIMIT THE RATES INTO VT/NH/ME, AND FFG IS ELEVATED FARTHER NORTH
DUE TO RECENT DRYNESS. FOR THIS REASON, AND AFTER COORDINATION WITH
THE WFOS, THE SLGT RISK WAS MODIFIED TO ENCOMPASS PRIMARILY
SOUTHERN NEW ENGLAND, WITH A BROADER MRGL RISK COVERING MOST OF THE
NORTHEAST.
..FOUR CORNERS STATES INTO THE CENTRAL/NORTHERN PLAINS
MONSOONAL FLOW, LIKELY TO BE ENHANCED BY GENEVIEVE MOVING OFFSHORE
BAJA CALIFORNIA, BRINGS ELEVATED MOISTURE OVER THE DESERT
SOUTHWEST THROUGH THE CENTRAL ROCKIES AND INTO THE CENTRAL AND
NORTHERN PLAINS. THE MORE SUPPRESSED RIDGE WILL ALLOW MULTIPLE
MESOSCALE/CONVECTIVELY AIDED SHORTWAVES TO PUSH OVER THE TOP/ACROSS
THE ROCKIES INTO THE PLAINS. IT IS POSSIBLE THAT SOME OF THESE
COULD RESULT IN LOCALLY HEAVIER RAIN ACROSS THE HIGH PLAINS OF CO,
AND THIS COULD FALL ATOP SOILS SATURATED FROM HEAVY RAIN ON D2. AT
THIS TIME CONFIDENCE IS NOT HIGH ENOUGH FOR AN UPGRADE RISK DUE
TO LOW PROBABILITIES AND UNCERTAINTY ABOUT STORM COVERAGE/SPEED,
BUT IT IS POSSIBLE A SLGT RISK MAY BE NEEDED FOR PARTS OF THE HIGH
PLAINS WITH LATER UPDATES.
..CENTRAL GULF COAST REGION INTO PARTS OF THE SOUTHEAST
A COLD FRONT STALLING ALONG THE GULF COAST WILL BE A FOCUS FOR SLOW
MOVING AND TRAINING THUNDERSTORMS ON WEDNESDAY. GUIDANCE CONTINUES
TO INDICATE A LOW-PROBABILITY THREAT FOR AT LEAST 3" OF RAIN DUE TO
TRAINING OF 1-2"/HR RAIN RATES WITHIN FAVORABLE THERMODYNAMICS.
THIS REGION CAN GENERALLY TOLERATE SIGNIFICANT RAIN RATES AND THIS
AMOUNT OF RAINFALL, BUT ANY MORE PRONOUNCED TRAINING COULD RESULT
IN ISOLATED FLASH FLOOD RELATED IMPACTS.
WEISS
DAY 4 AND DAY 5
VALID 12Z THU JUL 30 2026 - 12Z SAT AUG 01 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE LOWER MISSOURI AND MID TO UPPER MISSISSIPPI VALLEY...
20Z UPDATE...
FORECAST REMAINS LARGELY UNCHANGED. ONLY ADJUSTMENTS
TO THE DAY 4/5 EROS WAS TO EXTEND THE SLGT RISKS A TAD FARTHER
SOUTH GIVEN LATEST MODEL QPF AND THE TENDENCY FOR THUNDERTSORMS IN
NORTH-NORTHWESTERLY FLOW TO EXTEND AND POTENTIALLY BACKBUILD
FARTHER SOUTH THAN INITIALLY MODELED.
SNELL
PREVIOUS DISCUSSION...
..LOWER MISSOURI VALLEY INTO THE MID-UPPER MISSISSIPPI VALLEY
ON DAY 4 (THURSDAY-THURSDAY NIGHT), CONVECTIVELY-AIDED SHORTWAVE
ENERGY PROGRESSING EAST FROM THE CENTRAL-NORTHERN PLAINS WILL
AMPLIFY A BIT (DIG A BIT FARTHER SOUTH) UPON REACHING THE LOWER MO-
MID MS VALLEYS) DURING THIS TIME AS THE ~600DM 500MB HIGH BECOMES
CENTERED FARTHER WEST TOWARD THE FOUR CORNERS. THERE'S NEAR TO
ABOVE AVERAGE DISCREPANCY AMONGST THE 12Z GLOBAL GUIDANCE. THE
GFS/ GEFS MEAN/AIGFS ARE A BIT FARTHER EAST COMPARED TO THE
ECMWF/ECENS MEAN/EC AIFS, WITH THE CMC CAMP BASICALLY IN THE MIDDLE
IN TERMS OF EASTWARD PROGRESSION. IN ADDITION, THERE REMAINS
LATITUDINAL DIFFERENCES WITH THE HEAVIEST QPF, WITH THE 00Z UKMET
THE FARTHEST NORTH. GIVEN THE MCS/UPSCALE GROWTH POTENTIAL WITH
THIS SYSTEM, CONSIDERING THE INFLUX OF 2-2.25+ PWS PER THE
GUIDANCE, CONCENTRATED AREAS OF HEAVY RAIN ARE EXPECTED, ESPECIALLY
ACROSS THE CORN BELT GIVEN THE DEEP-LAYER MOISTURE PROFILE AND
HIGH SURFACE DEWPOINTS. CERTAINLY AN EVENT THAT WOULD WARRANT A
SLIGHT RISK, WHICH FOR NOW WE'VE CONFINED ACROSS EASTERN SD, FAR
EASTERN NE AND NORTHEAST KS, INTO NORTHWEST MO, WESTERN 2/3 OF
IOWA, AND SOUTHERN MN, WHERE THE GLOBAL ENSEMBLE PROBABILITIES OF
>3" IN 12/24 HOURS ARE HIGHEST.
ON DAY 5 (FRIDAY-FRIDAY NIGHT), HAVE ESSENTIALLY SHIFTED THE
SLIGHT RISK AREA FARTHER DOWNSTREAM (EAST-SOUTHEAST) PER THE GLOBAL
GUIDANCE CONSENSUS. GLOBALS ALL SHOW SPOTTY HEAVY 24HR RAINFALL
TOTALS, I.E. 3-5+ INCHES, THOUGH AGAIN WITH SOME SPATIAL SPREAD IN
THE GUIDANCE. ECENS QPF EXCEEDANCE PROBABILITIES HAVE COME UP FROM
THE PREVIOUS RUN, AND ARE CERTAINLY HIGHER COMPARED TO THE DAY 4
PERIOD (MORE EXPANDED AREA OF 3 TO 5 INCH PROBABILITIES).
..FOUR CORNERS STATES INTO THE CENTRAL/NORTHERN PLAINS
MONSOONAL FLOW AND ANOMALOUS DEEP-LAYER MOISTURE WILL MAINTAIN A
MARGINAL (ISOLATED) EXCESSIVE RAINFALL RISK OVER EASTERN AZ AND
MUCH OF MN (EXCEPT SE PORTION) INTO SOUTHEAST UT AND THROUGH MUCH
OF CO. THE EXPANDING MID/UPPER LEVEL RIDGE (600DM HEIGHTS AT 500
MB) WILL LIKELY LIMIT THE COVERAGE COMPARED TO RECENT DAYS,
ESPECIALLY BY FRIDAY.
..CENTRAL GULF COAST REGION INTO PARTS OF THE SOUTHEAST
HEAVY RAINFALL IS EXPECTED ALONG THE NEW ENGLAND CYCLONE'S
TRAILING FRONT NEAR THE FL/GA BORDER. MOISTURE SHOULD BE AMPLE AND
THERE COULD BE ENOUGH EFFECTIVE BULK SHEAR FOR CONVECTIVE
ORGANIZATION. THE INHERITED MARGINAL RISK AREAS FOR THURSDAY INTO
FRIDAY NIGHT SAW ONLY A FEW COSMETIC CHANGES TO BETTER FIT THE
MOST RECENT QPF GUIDANCE.
HURLEY
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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