318
FXUS02 KWBC 071950
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
350 PM EDT TUE OCT 7 2025
VALID 12Z FRI OCT 10 2025 - 12Z TUE OCT 14 2025
...TROPICAL MOISTURE TO BRING HEAVY RAINFALL HAZARDS TO PARTS OF
THE SOUTHWEST MUCH OF THE PERIOD...
...GUSTY WIND, COASTAL FLOOD, AND HEAVY RAINFALL THREATS EXPECTED
ALONG PARTS OF THE EAST COAST THIS WEEKEND INTO EARLY NEXT WEEK...
..GENERAL OVERVIEW
A DEEP UPPER LOW OFF THE PACIFIC NORTHWEST IS EXPECTED TO TURN
TOWARD THE COAST ON FRIDAY AND SWING EAST ACROSS THE INTERMOUNTAIN
WEST THROUGH THIS WEEKEND. THIS WILL DRAW TROPICAL MOISTURE FROM
PRISCILLA AND LEAD TO WIDESPREAD PRECIPITATION ACROSS THE WEST.
THERE IS CONTINUED MODEL SUPPORT FOR A COASTAL STORM TO DEVELOP OFF
THE CAROLINA COAST FRIDAY NIGHT AND DRIFT UP THE MID-ATLANTIC
COAST THROUGH THE WEEKEND. IN BETWEEN THESE SYSTEMS IS PERSISTENT
UPPER- LEVEL RIDGING CENTERED OVER TEXAS WITH AN AXIS THAT EXTENDS
UP THE GREAT PLAINS ON FRIDAY AND THEN GRADUALLY SHIFTS EAST TO THE
GREAT LAKES BY SUNDAY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE GUIDANCE GENERALLY SHOWS GOOD AGREEMENT ON THE OVERALL LARGE
SCALE PATTERN THROUGH THE PERIOD, BUT UNCERTAINTY OF THE DETAILS IN
ESPECIALLY THE PATTERN OUT WEST AND A DEVELOPING EAST COAST LOW
WOULD HAVE SIGNIFICANT IMPLICATIONS ON SENSIBLE WEATHER FOR THESE
AREAS. THE WPC FORECAST LEANED ON A GENERAL BLEND OF THE
DETERMINISTIC MODELS FOR DAYS 4 AND 5, GRADUALLY INCREASING
WEIGHTING OF THE ENSEMBLE MEANS LATER IN THE PERIOD TO HELP WITH
GROWING UNCERTAINTY. THIS MAINTAINED GOOD AGREEMENT WITH THE PRIOR
SHIFT AS WELL.
OUT WEST, CONFIDENCE IS HIGH ON THE UPPER LOW CENTER TRACKING
TOWARDS THE OR/CA BORDER, BUT THE EVOLUTION OF THIS TROUGH OVER THE
WEST INTO NEXT WEEK AND ADDITIONAL ENERGY DROPPING INTO THE TROUGH
IS VERY UNCERTAIN. THE MAIN OUTLIER SEEMS TO BE THE CMC WHICH
SPINS UP AN ADDITIONAL CUT-OFF CLOSED LOW OVER THE WEST EARLY NEXT
WEEK AND PULLS IT WESTWARD TO OFF THE NORTHERN CA COAST. THE ECMWF
AND GFS, WITH ENSEMBLE MEAN SUPPORT, SHOW A MORE EASTWARD
PROGRESSION (BUT THE GFS MAY BE TOO FAST). THE PREFERENCE IS
TOWARDS THE ECMWF FOR THIS SYSTEM WHICH IS CLOSER TO THE ENSEMBLE
MEANS. THE EVOLUTION OF THIS TROUGH WILL IMPACT MOISTURE ADVECTION
INTO THE SOUTHWEST FROM PRISCILLA AND ANOTHER LIKELY TROPICAL
SYSTEM BEHIND IT.
THE CONSENSUS CONTINUES TO FAVOR COASTAL CYCLOGENESIS OFF THE
CAROLINAS FRIDAY NIGHT THAT DRIFTS NORTHWARD TO AT LEAST THE
SOUTHERN MID-ATLANTIC COAST THIS WEEKEND. THERE ARE PLACEMENT
CONCERNS WITH THIS EVEN AS EARLY AS SUNDAY WHICH WOULD IMPACT HOW
MUCH RAINFALL MAKES IT INLAND VS STAYS OFFSHORE. THE CMC REMAINS AN
EASTERN OUTLIER SOLUTION COMPARED TO THE ECMWF, GFS, AND EC-AIFS.
UNCERTAINTY REALLY INCREASES AFTER SUNDAY, WITH GUIDANCE SUGGESTING
IT MAY GET STUCK IN BETWEEN STRONG RIDGING OVER THE SOUTHERN TO
MIDWEST U.S. AND THE WESTERN ATLANTIC. SOME GUIDANCE PULLS IT
NORTHWARD AND SPINS OFF THE MID-ATLANTIC OR NORTHEAST COAST, WHILE
OTHER MODELS ACTUALLY PULL IT BACK SOUTHWARD. WPC PREFERS A MIDDLE
GROUND APPROACH FOR NOW, CONSISTENT WITH THE ENSEMBLE MEANS.
..WEATHER/HAZARDS HIGHLIGHTS
AN INFLUX OF TROPICAL MOISTURE AHEAD OF PRISCILLA AND AN OPENING
TROUGH ALONG THE WEST COAST IS EXPECTED ACROSS THE INTERMOUNTAIN
WEST FRIDAY THROUGH THE WEEKEND. FOR FRIDAY, INCREASED CLOUD COVER
AND LIMITED INSTABILITY ARE DETERRING FACTORS TOWARDS EXCESSIVE
RAINFALL, BUT HIGHER OVERALL QPF, RAINFALL IN THE DAY 3 PERIOD, AND
LOWER FLASH FLOOD GUIDANCE WARRANTED THE ADDITION OF A SLIGHT RISK
TO THE DAY 4/FRIDAY ERO FROM NORTHERN ARIZONA TO SOUTHWEST
COLORADO. GREATER FORCING FROM THE APPROACHING TROUGH (ALONG WITH
LIKELY WET ANTECEDENT CONDITIONS) ALLOW FOR AN EXPANSION OF THE
SLIGHT RISK FOR THE NEW DAY 5 ERO COVERING MUCH OF ARIZONA, WESTERN
NEW MEXICO, AND WESTERN COLORADO. THE TROPICAL MOISTURE SURGE
CONTINUES TO OVERSPREAD THE INTERMOUNTAIN WEST ON SUNDAY AND
MONDAY, PARTICULARLY WITH A PREFERRED SLOWER EJECTION OF THE TROUGH
FROM THE WEST COAST, SO RAINFALL LOOKS TO BE A THREAT THROUGH MUCH
OF THE PERIOD. EXPECT MOUNTAIN SNOW UNDER THE UPPER TROUGH
PASSAGE.
LOW PRESSURE WILL LIKELY DEVELOP ALONG A STALLED BOUNDARY OFF THE
CAROLINA COAST FRIDAY NIGHT WITH A SURGE OF HEAVY RAIN SLOWLY
LIFTING NORTH INTO THE SOUTHERN MID-ATLANTIC THROUGH THE WEEKEND.
THE DAY 4 MARGINAL ERO IS MAINTAINED ALONG THE CAROLINA COAST FOR
FRIDAY, BUT MUCH OF THE GUIDANCE DOES SHOW THE HEAVIEST RAINFALL
REMAINING OFFSHORE. THERE IS A MARKED INCREASE IN QPF FOR SATURDAY
AS THE COASTAL LOW MOVES VERY SLOWLY OFFSHORE AND DEEPENS. A SLIGHT
RISK ERO IS IN PLACE FOR DAY 5/SATURDAY IN EASTERN NORTH CAROLINA.
IN ADDITION TO HEAVY RAIN, GUSTY ONSHORE WINDS WILL ALSO ACCOMPANY
THIS SYSTEM AND COMBINED WITH HIGHER THAN NORMAL TIDES, INCREASES
THE THREAT FOR COASTAL FLOODING ACROSS MUCH OF THE CAROLINAS TO
SOUTHERN MID- ATLANTIC.
COOL CONDITIONS WITH MAX TEMPERATURES FIVE OR SO DEGREES BELOW
NORMAL CONTINUE ALONG THE EASTERN SEABOARD FRIDAY. MEANWHILE,
RIDGING OVER TEXAS AMPLIFIES UP THE ROCKIES AND GREAT PLAINS THIS
WEEKEND WHICH WILL MAINTAIN ABOVE NORMAL TEMPERATURES. COOL
CONDITIONS ARE EXPECTED OVER THE WEST BEHIND THE COLD FRONT ONCE
THE LOW OFF THE PACIFIC NORTHWEST EJECTS EAST.
SANTORELLI/JACKSON
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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