141
FXUS02 KWBC 270749
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
349 AM EDT SAT SEP 27 2025
VALID 12Z TUE SEP 30 2025 - 12Z SAT OCT 04 2025
...POTENTIAL TROPICAL CYCLONE 9 MAY BRING TROPICAL IMPACTS TO THE
SOUTHEAST AND MID-ATLANTIC NEXT WEEK...
..OVERVIEW
THE EXTENDED PERIOD WILL HAVE MEAN TROUGHING OVER THE WEST,
NARROWING RIDGING OVER THE CENTRAL CONUS AND LOW PRESSURE OVER THE
SOUTHEAST. THIS PATTERN WILL BE FAVORABLE FOR A PROLONGED WET
PERIOD FOR THE SOUTHEAST AND FOR PARTS OF THE WEST THAT COULD LEAD
TO FLASH FLOODING. THE HIGHEST AREA OF CONCERN WILL BE PORTIONS OF
THE SOUTHEAST AND MID-ATLANTIC THAT MAY BE IMPACTED BY POTENTIAL
TROPICAL CYCLONE 9 NEXT WEEK. HOWEVER, THE FORECAST FOR THESE
REGIONS IS HIGHLY UNCERTAIN GIVEN HIGH UNCERTAINTY IN THE FORECAST
TRACK OF THE SYSTEM. MOST OF THE CENTRAL U.S. AND NORTHEAST WILL
REMAIN DRY THROUGH THE PERIOD UNDER THE INFLUENCE OF HIGH PRESSURE.
PRECIPITATION CHANCES MAY INCREASE LATER NEXT WEEK ACROSS THE
NORHT-CENTRAL U.S. AS A FRONTAL BOUNDARY MOVES ACROSS THE WEST AND
EMERGES IN THE PLAINS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LARGE SCALE PATTERN CONTINUES TO BE IN FAIRLY GOOD AGREEMENT
WITH RIDGING OVER THE CENTRAL PART OF THE CONUS WITH APPROACHING
SYSTEMS TO THE WEST AND EAST COASTS. MULTIPLE FRONTAL SYSTEMS WILL
EJECT FROM AN UPPER TROUGH APPROACHING THE PACIFIC NORTHWEST WHICH
WILL SUPPORT A MULTI-DAY WET PERIOD. INDIVIDUAL SYSTEMS RAISE
UNCERTAINTY IN HOW INDIVIDUAL MODELS HANDLE SHORTWAVE ENERGY
MOVING THROUGH THE TROUGH.
THE FORECAST IS MUCH MORE COMPLICATED FOR THE EAST GIVEN A HIGH
AMOUNT OF UNCERTAINTY SURROUNDING THE EVOLUTION OF POTENTIAL
TROPICAL CYCLONE 9, WHICH IS CURRENTLY FORECAST TO MOVE TOWARDS THE
SOUTHEAST COAST WHILE STRENGTHENING NEXT WEEK. SOME MODELS BRING
THE TROPICAL SYSTEM INLAND IN THE CAROLINAS, SOME STALL THE SYSTEM
RIGHT OVER THE CAROLINA COAST, AND SOME STALL THE SYSTEM FURTHER
AWAY FROM THE COAST BEFORE SWINGING THE SYSTEM OUT INTO THE
ATLANTIC. THE ULTIMATE EVOLUTION WILL DEPEND ON THE SYSTEM'S
INTERACTIONS WITH HURRICANE HUMBERTO TO THE EAST AND HIGH PRESSURE
STRENGTHENING TO THE NORTH. IF THE STRONG HIGH SHIFTS EAST, THE
SYSTEM COULD MOVE INLAND, BUT IF THE HIGH REMAINS DUE NORTH, A
STALLED SOLUTION WOULD BE FAVORED.
WPC MAINTAINED CONTINUITY BY BLENDING THE SOLUTIONS OF THE 12Z
ECMWF/CMC/UKMET/GFS, WITH HEAVIER WEIGHT PLACED ON THE ECMWF AND
GFS THAN THE CMC AND UKMET, THROUGH MIDWEEK. BY THURSDAY AND
FRIDAY, ENSEMBLE MEANS FROM THE GEFS AND ECENS WERE ADDED IN
INCREASING AMOUNTS, MAKING UP TO 60% OF THE BLEND, WHICH HELPED TO
SMOOTH OUT LARGE DIFFERENCES IN THE DETERMINISTIC MODELS.
..WEATHER/HAZARDS HIGHLIGHTS
WET AND UNSETTLED CONDITION EXPECTED FOR PORTIONS OF THE MID-
ATLANTIC AND SOUTHEAST AS ANOMALOUS MOISTURE ASSOCIATED WITH
POTENTIAL TROPICAL CYCLONE 9 MAINTAIN PRECIPITATION CHANCES, WITH
A HEAVY RAIN AND FLASH FLOOD THREATS, THROUGH MID-WEEK NEAR A
LINGERING FRONTAL BOUNDARY. THE HIGHEST RISK OF FLASH FLOODING
WILL LIKELY FOCUS OVER THE COASTAL CAROLINAS, BUT RAINFALL AMOUNTS
ARE HIGHLY UNCERTAIN AND WILL DEPEND ON THE TRACK OF THE SYSTEM.
SOME MODELS SUGGEST MUCH HIGHER RAINFALL AMOUNTS ARE POSSIBLE WHILE
SOME SUGGEST LOWER AMOUNTS. THE MARGINAL AND SLIGHT RISKS WERE
MAINTAINED FOR D4 WITH MINOR RESHAPING OF BOTH AREAS TO REFLECT
THE LATEST QPF TREND AND WPC QPF. THERE WAS NOTICEABLE SLOWING OF
THE POTENTIAL TROPICAL CYCLONE ALONG WITH A SMALL SOUTHWARD SHIFT,
THIS COULD ALLOW THE THREAT FOR THE HEAVY RAIN AND FLASH FLOODING
TO PERSIST THROUGH THE WEEK. A MARGINAL RISK WAS RAISED FOR THE
CAROLINAS FOR DAY 5. REGARDLESS OF HOW THE RAINFALL FORECAST TURNS
OUT, THE SOUTHEAST COAST WILL LIKELY EXPERIENCE DANGEROUS SURF AND
RIP CURRENT CONDITIONS EARLY NEXT WEEK, AND SOME COASTAL AREAS MAY
EXPERIENCE STRONG WINDS.
PACIFIC MOISTURE AHEAD OF THE UPPER TROUGH WILL RESULT IN
CONTINUED RAIN CHANCES FOR THE WEST COAST AND INTERMOUNTAIN WEST ON
MONDAY AND TUESDAY. PRECIPITATION MAY BE ENHANCED OVER NORTHERN
CALIFORNIA AND SOUTHERN OREGON AS A SLOW-MOVING FRONTAL SYSTEM
MOVES ONSHORE, RESULTING IN LOCALIZED FLASH FLOODING CHANCES AND A
MARGINAL RISK OF EXCESSIVE RAINFALL ON MONDAY AND TUESDAY.
PRECIPITATION CHANCES SHOULD DECREASE ON WEDNESDAY AND THURSDAY,
BUT PRECIPITATION WILL LIKELY LINGER OVER THE PACIFIC NORTHWEST AND
NORTHERN ROCKIES. PRECIPITATION CHANCES MAY ALSO INCREASE LATER
NEXT WEEK ACROSS THE NORTH-CENTRAL U.S. ONCE THE FRONTAL SYSTEM
PUSHES ACROSS THE MOUNTAIN AND EMERGES IN THE PLAINS.
WITH UPPER RIDGING BUILDING OVERHEAD WARMER THAN SEASONAL AVERAGE
TEMPERATURES ARE EXPECTED TO CONTINUE FOR THE NORTHERN PLAINS.
DAILY MAXIMUMS OF 10 TO 20 DEGREES ABOVE NORMAL WILL BE POSSIBLE
FOR THE UPPER MIDWEST REGION WHILE BELOW AVERAGE TEMPERATURES WILL
OCCUR IN THE WEST AND SOUTHEAST DUE TO UPPER TROUGHING AND
POTENTIAL RAINFALL.
CAMPBELL/DOLAN
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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