157
FXUS02 KWBC 281815
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
215 PM EDT MON JUL 28 2025
VALID 12Z THU JUL 31 2025 - 12Z MON AUG 04 2025
...HEAVY RAIN AND FLASH FLOODING POTENTIAL ALONG THE EAST COAST
LATER THIS WEEK...
..OVERVIEW
A REASONABLY STRONG COLD FRONT FOR LATE JULY-EARLY AUGUST IS
FORECAST TO PUSH SOUTHWARD ACROSS THE EAST AT THE LEADING EDGE OF
AN UPPER TROUGH LATER THIS WEEK INTO THE WEEKEND. MOISTURE AND
INSTABILITY ALONG AND AHEAD OF THE FRONT WILL PROMOTE HEAVY TO
EXCESSIVE RAINFALL IN THUNDERSTORMS THAT COULD CAUSE LOCALIZED
FLASH FLOODING. THE FRONT AND UPPER TROUGH SHOULD ALSO DISPLACE
UPPER RIDGING CAUSING A HEAT WAVE IN THE SHORT TERM, LIMITING THE
HEAT TO THE SOUTHEAST THURSDAY AND GRADUALLY LESSENING IN SCOPE AND
MAGNITUDE BY THE WEEKEND. THE FRONT WILL STRETCH WESTWARD INTO THE
SOUTH-CENTRAL U.S. AND BEND NORTHWARD ACROSS MUCH OF THE PLAINS.
COMPLEXES OF SHOWERS AND STORMS ARE LIKELY IN THE INTERIOR
NORTHWEST TO THE CENTRAL U.S. FOR MULTIPLE DAYS WITH SHORTWAVES
MOVING THROUGH THE FLATTENING UPPER FLOW. MONSOONAL MOISTURE COULD
CONTINUE TO CAUSE SHOWERS AND STORMS IN PARTS OF THE SOUTHWEST
THROUGH LATE WEEK WITH LESSENING RAIN CHANCES BY THE WEEKEND.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE REMAINS IN GOOD AGREEMENT FOR THE EARLY MEDIUM
RANGE PERIOD LATE WEEK. UPPER HIGHS EMBEDDED WITHIN A SOUTHERN U.S.
RIDGE WILL BE IN PLACE, GENERALLY RETROGRADING FROM THE SOUTHERN
PLAINS TO SOUTHWEST AND FROM THE WESTERN ATLANTIC ACROSS FLORIDA
INTO THE GULF. THE RIDGE AXIS EXTENDS INTO THE HIGH PLAINS WHILE AN
UPPER TROUGH EXTENDS FROM EASTERN CANADA INTO THE EASTERN U.S. ON
THURSDAY-FRIDAY. THE WPC FORECAST USED A BLEND OF THE LATEST
00Z/06Z GUIDANCE TO START, THOUGH THE 00Z CANADIAN WAS FIRST TO
BECOME MOST DISSIMILAR IN THE WEST BY THE WEEKEND. SMALLER SCALE
FEATURES COULD STILL CAUSE DIFFERENCES IN FRONTAL PLACEMENT AND QPF
THOUGH.
BY THE WEEKEND, MODEL DIFFERENCES START TO INCREASE AS THE PATTERN
BECOMES MORE QUASI-ZONAL AND UNCERTAINTY IN SHORTWAVE
TRACK/TIMING/AMPLITUDE INCREASES. THE LARGEST GUIDANCE DIFFERENCE
WAS THE PATTERN IN THE NORTHWEST BY SUN-MON. THIS WILL BE
INFLUENCED BY A LARGE NORTHEAST PACIFIC UPPER LOW WITH SOMEWHAT
UNCERTAIN PLACEMENT. MODELS HAVE BECOME LESS CLUSTERED AND THE
AI/ML MODELS/ENSEMBLES HAVE TRENDED TOWARD INCREASED WESTERN
TROUGHING (EVEN DOWNSTREAM INTO THE ROCKIES). THIS WAS IN CONTRAST
TO SOME DYNAMICAL MODELS SHOWING INCREASED RIDGING OVER THE FOUR
CORNERS A THE SAME TIME. THUS, USED A MAJORITY ENSEMBLE MEAN
WEIGHTING BY THE END OF THE PERIOD MOSTLY WITH THE ECMWF ENSEMBLE
MEAN.
..WEATHER/HAZARDS HIGHLIGHTS
THE COLD FRONT PUSHING THROUGH THE EAST WILL PROVIDE A FOCUS FOR
AMPLE MOISTURE AND INSTABILITY TO POOL WHILE THERE SHOULD BE
INCREASING DYNAMICAL SUPPORT IN THE FORM OF THE RIGHT ENTRANCE
REGION OF THE UPPER JET. HIGH RAIN RATES IN WIDESPREAD
THUNDERSTORMS SHOULD LEAD TO A FLASH FLOODING RISK -- A SLIGHT RISK
REMAINS IN PLACE IN THE DAY 4/THURSDAY ERO FOR THE MID- ATLANTIC,
PARTS OF WHICH ARE STARTING WITH WETTER THAN AVERAGE ANTECEDENT
CONDITIONS THAT COULD AUGMENT THE FLOODING RISK. THE SLIGHT
INCLUDES SOUTHERN NEW ENGLAND/NYC DUE TO UNCERTAINTY IN HOW QUICKLY
THE FRONT MAY PROGRESS SOUTHWARD. BY FRIDAY THE FRONT IS FORECAST
TO PUSH INTO THE CAROLINAS, AND A SLIGHT RISK IS NOTED FOR THE DAY
5/FRIDAY ERO INTO THE SOUTHERN APPALACHIANS AND EASTERN GEORGIA
WITH SIMILAR ENVIRONMENTAL FACTORS AS THURSDAY FARTHER NORTH. THE
CAROLINAS MAY SEE ADDITIONAL CONVECTION INTO THE WEEKEND. THE FRONT
STRETCHING WEST ACROSS THE GULF COAST STATES IN A MOIST AND
UNSTABLE ENVIRONMENT COULD PROMOTE SCATTERED DIURNAL THUNDERSTORMS
THERE THROUGH LATE WEEK INTO THE WEEKEND, AND MARGINAL RISKS ARE IN
PLACE IN THE DAY 4/5 EROS DUE TO HIGH RAIN RATES THAT MAY OVERCOME
THE HIGH FLASH FLOOD GUIDANCE AND/OR FALL ATOP URBAN AREAS.
FARTHER WEST AS THE FRONT BENDS BACK INTO THE PLAINS, ROUNDS OF
RAIN AND THUNDERSTORMS ARE LIKELY WITH POSSIBLY MULTIPLE MCSS. SOME
SHORTWAVE FORCING AND ABOVE NORMAL MOISTURE AND INSTABILITY SHOULD
LEAD TO HIGH RAIN RATES, AND SOME AREAS COULD SEE REPEATING ROUNDS
OF STORMS WITH THE FRONT STALLING. MODELS HAVE TRENDED TOWARD AN
EARLIER FOCUS FOR HEAVIER RAINFALL OVER CO INTO D3 RATHER THAN D4,
AND THE SLIGHT RISK WAS MOVED INTO THE D3 PERIOD. BROAD MARGINAL
RISKS COVER MUCH OF THE HIGH PLAINS ON BOTH DAYS 4 AND 5 AND BACK
INTO THE NORTHERN ROCKIES/HIGH PLAINS NEAR THE BACK END OF THE
FRONT AS MUCH HIGHER THAN AVERAGE INSTABILITY (PER THE EXTREME
FORECAST INDEX) IS IN PLACE. FARTHER SOUTH, MONSOONAL MOISTURE
(WITH PRECIPITABLE WATER VALUES GENERALLY IN THE 75TH-90TH
PERCENTILE) WILL BE PRESENT OVER PARTS OF THE SOUTHWEST ALONG WITH
SOME INSTABILITY, BUT OVERALL THE MONSOON SEASON REMAINS DRIER THAN
NORMAL ESPECIALLY FOR UT/AZ. MARGINAL RISKS ARE IN PLACE IN THE
DAYS 4 AND 5 EROS FOR PARTS OF THE SOUTHWEST, REACHING INTO THE
CENTRAL ROCKIES/HIGH PLAINS AS AS THE MONSOONAL MOISTURE MEETS THE
FRONTAL SYSTEM TO THE NORTH. MOISTURE LOOKS TO LESSEN IN THE
SOUTHWEST BY THE WEEKEND.
ANOTHER HOT DAY IS FORECAST FOR THE CAROLINAS INTO GEORGIA AND
FLORIDA THURSDAY AHEAD OF THE COLD FRONT AND UNDER WHAT REMAINS OF
THE SHORT RANGE UPPER RIDGE. HEATRISK IS MAINLY IN THE MAJOR (LEVEL
3/4) CATEGORY WITH SOME EMBEDDED EXTREME (LEVEL 4/4) AREAS AS
TEMPERATURES REACH WELL INTO THE 90S WITH HIGHER HEAT INDICES
(NEARING 110F), WHILE MORNING LOWS WELL INTO THE 70S AND NEARING 80
WILL NOT PROVIDE MUCH RELIEF. THE COLD FRONT GRADUALLY PASSING
THROUGH THE SOUTHEAST WILL BRING MODERATING TEMPERATURES, AND
FLORIDA WILL BE THE LAST TO SEE RELIEF FROM THE HEAT THIS WEEKEND.
COOLER THAN AVERAGE TEMPERATURES (ESPECIALLY HIGHS) ARE LIKELY IN
THE NORTHERN/CENTRAL PLAINS ON THE COOL SIDE OF THE FRONT AND WITH
THE CLOUDS AND RAIN CHANCES -- A FEW LOCATIONS MAY EVEN CHALLENGE
RECORD COOL MAXES FOR THE DAY (LOW 70S). MEANWHILE THE SOUTHWEST
CAN EXPECT SEASONABLE HEAT (NEAR TO SLIGHTLY ABOVE AVERAGE), WITH
THE LOWER DESERT AREAS SEEING TEMPERATURES 105-110 DEGREES.
FRACASSO/TATE
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION FORECAST (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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