199
FXUS02 KWBC 260735
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
335 AM 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
DURING THE MEDIUM RANGE PERIOD AN UPPER TROUGH/LOW WILL REMAIN
STALLED OVER THE SOUTHWEST BLOCKED BY STRONG RIDGING DOWNSTREAM. A
DEEP UPPER LOW AND TROUGH IS EXPECTED TO ADVANCE TOWARD THE WEST
COAST EARLY NEXT WEEK, LIFTING THE UPPER LOW OUT OF THE SOUTHWEST
AND INCREASING PRECIPITATION CHANCES ACROSS THE WEST. THE CENTRAL
U.S. WILL REMAIN MOSTLY DRY THROUGH THE PERIOD UNDER THE INFLUENCE
OF HIGH PRESSURE RIDGING, BUT THE EASTERN U.S. MAY BE ENTERING A
WETTER PATTERN. A COLD FRONT WILL MOVE ACROSS THE NORTHEAST SUNDAY
INTO MONDAY WHILE A STATIONARY FRONT LINGERS ALONG THE SOUTHEAST
AND MID-ATLANTIC COASTS. THERE MAY BE A CHANCE FOR HEAVY RAINFALL
AND FLASH FLOODING OVER PORTIONS OF THE SOUTHEAST AND MID-ATLANTIC
THROUGH WEDNESDAY, BUT THAT WILL DEPEND ON THE EVOLUTION OF A
LIKELY TROPICAL LOW FORMING NEAR THE BAHAMAS OVER THE NEXT FEW
DAYS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST SUITE OF GUIDANCE HAS DECENT LARGE SCALE AGREEMENT WITH
CONTINUED VARIANCES IN REGARDS TO THE BOTH THE WEST COAST AND
SOUTHEAST/MID-ATLANTIC REGION. THE GREATEST UNCERTAINTY PREVAILS WHETHER
OR NOT A TROPICAL DISTURBANCE WILL MOVE INLAND OVER THE CAROLINAS
OR REMAIN OFFSHORE. SOLUTIONS ARE TIPPING TOWARD A MORE INLAND PATH
WHICH SUPPORTS INCREASED CLOUD COVER, QPF AND THE POTENTIAL FOR
FLASH FLOODING THREATS.
THE EVOLUTION WILL ULTIMATELY BE DETERMINED BY INTERACTIONS
BETWEEN THE TROPICAL LOW, HURRICANE HUMBERTO TO THE EAST, A FRONTAL
BOUNDARY TO THE NORTH, AND AN UPPER TROUGH OVER THE EAST. PLEASE
REFER TO THE NHC FOR THE LATEST INFORMATION ON THIS SYSTEM. THERE
IS STILL A LARGE AMOUNT OF UNCERTAINTY SURROUNDING THE EVOLUTION
AND TRACK OF THIS LOW, AND THE FORECAST WILL LIKELY CHANGE OVER THE
NEXT FEW DAYS.
FOR THE WEST, THE UNCERTAINTY COMES FROM TIMING AND EVOLUTION
DIFFERENCES OF LOW PRESSURE SYSTEMS MOVING ONSHORE FROM THE
PACIFIC. THIS UNCERTAINTY WILL AFFECT PRECIPITATION LOCATION AND
AMOUNTS NEAR THE COAST, ESPECIALLY MONDAY INTO TUESDAY WHEN LOCALLY
HEAVY PRECIPITATION WILL BE POSSIBLE.
THE PREFERRED BLEND FOR THE EXTENDED PERIOD COMPRISED OF THE 12Z
ECMWF/CMC/UKMET AND 18Z GFS THROUGH WEDNESDAY; INCLUDED THE 12Z
ECENS AND GEFS MEANS TO HELP SMOOTH OUT MODEL DIFFERENCES FOR
THURSDAY AND FRIDAY.
..WEATHER/HAZARDS HIGHLIGHTS
DAILY SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE NEAR A LINGERING
FRONTAL BOUNDARY ALONG THE EAST COAST THROUGH EARLY NEXT WEEK. ANOMALOUS
MOISTURE WITH A POSSIBLE TROPICAL CONNECTION WILL MAINTAIN AT
LEAST A LOCALIZED HEAVY RAINFALL THREAT FOR THE MID-
ATLANTIC/CAROLINAS AND PARTS OF THE APPALACHIANS. A MARGINAL RISK
OF EXCESSIVE RAINFALL FOR MOST OF THE MID-ATLANTIC AND CAROLINAS
ON MONDAY AND TUESDAY. INCREASING TROPICAL MOISTURE INTO THE REGION
WILL LIKELY LEAD TO ENHANCED PRECIPITATION IN THE CAROLINAS ON
MONDAY AND INTO PARTS OF VIRGINIA ON TUESDAY. A SLIGHT RISK OF
EXCESSIVE RAINFALL WAS MAINTAINED FOR THE CAROLINA COASTS MONDAY
AND A NEW AREA RAISED FOR SOUTHEAST VIRGINIA AND EASTERN NORTH
CAROLINA FOR TUESDAY. THE THREAT MAY CONTINUE BEYOND TUESDAY
DEPENDING ON THE EVOLUTION OF THE TROPICAL SYSTEMS OFF THE
SOUTHEAST COAST, AND THERE ARE PIECES OF GUIDANCE SUGGESTING
SIGNIFICANTLY HIGHER RAINFALL AMOUNTS WILL BE POSSIBLE. THE
RAINFALL FORECAST WILL LIKELY CHANGE OVER THE NEXT FEW DAYS.
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 AREAS MAY EXPERIENCE INCREASED
WINDS.
PACIFIC MOISTURE AHEAD OF AN UPPER LOW OVER SOUTHERN CALIFORNIA
WILL RESULT IN RAINFALL CONTINUING INTO EARLY NEXT THOUGH WITH
LESSER INTENSITY THAN THE SHORT RANGE. ANOMALOUS MOISTURE AND
SUFFICIENT INSTABILITY WILL CONTINUE TO SUPPORT AT LEAST A
LOCALIZED FLASH FLOOD THREAT INTO MONDAY, PARTICULARLY FOR
VULNERABLE BURN SCARS. THIS REGION REMAINS HIGHLIGHTED WITH A
MARGINAL RISK OF EXCESSIVE RAINFALL FOR MONDAY.
AMPLIFIED TROUGHING OVER THE PACIFIC NORTHWEST WILL LEAD TO
INCREASING PRECIPITATION AS IT SPREADS INLAND TO THE NORTHERN
GREAT BASIN/ROCKIES. THE HEAVIEST PRECIPITATION IS EXPECTED FROM
WESTERN WASHINGTON TO NORTHERN CALIFORNIA AND THE SIERRA NEVADA. A
MARGINAL RISK OF EXCESSIVE RAINFALL WAS MAINTAINED FOR MONDAY FOR
NORTHERN CALIFORNIA AND ADDED FOR TUESDAY. SOME SNOW MAY FALL IN
THE HIGHEST ELEVATIONS OF THE WEST AS WELL.
WARMER THAN AVERAGE TEMPERATURES WILL SHIFT INTO THE NORTHERN
PLAINS AND MAINTAIN 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 NORMAL TEMPERATURES OVER THE SOUTHWEST
WILL EXPAND NORTHWARD ALONG MUCH OF THE WEST COAST BY NEXT WEEK.
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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