370
FXUS02 KWBC 262001
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
401 PM EDT FRI SEP 26 2025
VALID 12Z MON SEP 29 2025 - 12Z FRI OCT 03 2025
...A TROPICAL DISTURBANCE MAY BRING TROPICAL IMPACTS TO THE
SOUTHEAST AND MID-ATLANTIC NEXT WEEK...
..OVERVIEW
THE UPPER LEVEL PATTERN WILL FEATURE MEAN TROUGHING OVER THE WEST,
LOW PRESSURE OVER THE SOUTHEAST, AND NARROW RIDGING IN BETWEEN.
THIS PATTERN WILL SUPPORT ENHANCED PRECIPITATION CHANCES IN THE
WEST AND SOUTHEAST, WITH CHANCES FOR HEAVY RAIN 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 A TROPICAL
DISTURBANCE 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
MODEL GUIDANCE IS GENERALLY IN AGREEMENT ON THE LARGE SCALE UPPER
LEVEL PATTERN WITH SOME UNCERTAINTY SURROUNDING FEATURES
APPROACHING THE WEST AND EAST COASTS. IN THE WEST, THERE IS
INCREASED AGREEMENT ON THE EVOLUTION OF THE UPPER TROUGH MOVING
INLAND, BUT THERE ARE DIFFERENCES IN HOW INDIVIDUAL MODELS HANDLE
SHORTWAVE ENERGY MOVING THROUGH THE TROUGH. THIS HAS LED TO
DIFFERENCES IN THE EVOLUTION OF PACIFIC FRONTAL SYSTEMS MOVING
ONSHORE. FOR NOW, IT SEEMS LIKE A MIDDLE OF THE ROAD SOLUTION
WORKED BEST TO REPRESENT POTENTIAL TIMING AND POSITION OF THESE
SYSTEMS.
THE FORECAST IS MUCH MORE COMPLICATED FOR THE EAST GIVEN A HIGH
AMOUNT OF UNCERTAINTY SURROUNDING THE EVOLUTION OF THE TROPICAL
DISTURBANCE MOVING TOWARDS THE SOUTHEAST COAST 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. AFTER COORDINATING WITH
THE NATIONAL HURRICANE CENTER, THE CURRENT FORECAST THINKING IS TO
STALL THE SYSTEM VERY CLOSE TO THE CAROLINA COAST. THIS SOLUTION
IS SIMILAR TO THE 00/12Z ECMWF SOLUTIONS AND MAY RESULT IN A
PROLONGED HEAVY RAINFALL EVENT FOR COASTAL AREAS OF THE CAROLINAS.
WPC'S AFTERNOON FORECAST BLEND WAS COMPRISED OF THE 00Z
ECMWF/CMC/UKMET AND 06Z GFS, WITH HEAVIER WEIGHT PLACED ON THE
ECMWF AND GFS THAN THE CMC AND UKMET, FOR MONDAY THROUGH WEDNESDAY.
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
SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE NEAR A LINGERING
FRONTAL BOUNDARY OVER THE MID-ATLANTIC AND SOUTHEAST EARLY NEXT
WEEK. ANOMALOUS MOISTURE WITH A TROPICAL CONNECTION WILL MAINTAIN
PRECIPITATION CHANCES, WITH A HEAVY RAIN AND FLASH FLOOD THREATS,
THROUGH MID-WEEK. 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. FOR NOW, THERE IS A MARGINAL RISK OF
EXCESSIVE RAINFALL ACROSS THE CAROLINAS AND VIRGINIA WITH A SLIGHT
RISK FOR THE EASTERN CAROLINAS AND SOUTHEASTERN VIRGINIA ON MONDAY
AND TUESDAY. IF THE SYSTEM MOVES INLAND AT ALL, THERE MAY BE
ENHANCED PRECIPITATION OVER UPSLOPE AREAS OF THE APPALACHIANS THAT
WOULD LEAD TO A HIGHER FLASH FLOOD RISK. THE HEAVY RAIN AND FLASH
FLOOD THREATS MAY CONTINUE BEYOND TUESDAY IF THE SYSTEM STALLS NEAR
THE COAST, WITH PRECIPITATION CHANCES EXTENDING THROUGH THURSDAY
AND FRIDAY. 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 INCREASED 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.
WARMER THAN AVERAGE TEMPERATURES WILL PERSIST ACROSS THE NORTHERN
PLAINS AS UPPER RIDGING BUILDS OVER THE REGION NEXT WEEK. DAYTIME
HIGHS COULD BE 10-20 DEGREES ABOVE NORMAL FOR PARTS OF THE UPPER
MIDWEST. BELOW AVERAGE TEMPERATURES ARE EXPECTED ACROSS MUCH OF THE
WEST AND SOUTHEAST DUE TO UPPER TROUGHING AND POTENTIAL RAINFALL.
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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