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FXUS21 KWNC 241805
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SEPTEMBER 24 2026
SYNOPSIS: FRONTAL ACTIVITY ALONG WITH MOIST, SOUTHERLY FLOW FROM THE GULF OF
AMERICA PERSISTING FROM WEEK-1 INTO WEEK-2 SUPPORTS A CONTINUED RISK OF HEAVY
PRECIPITATION THROUGHOUT MUCH OF THE SOUTHEASTERN CONTIGUOUS U.S. (CONUS) EARLY
IN THE PERIOD. POTENTIALLY STRONG PRESSURE GRADIENTS FAVORED ALONG THE WEST
COAST SUPPORT INCREASED CHANCES FOR EPISODES OF HIGH WINDS ACROSS PORTIONS OF
THE WEST COAST. AN AREA OF STRENGTHENING MID-LEVEL LOW PRESSURE TO THE SOUTH
OF THE ALEUTIANS IS EXPECTED TO BRING AN INCREASED RISK OF HEAVY PRECIPITATION
AND HIGH WINDS TO PARTS OF SOUTHERN COASTAL ALASKA.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR MUCH OF THE SOUTHEASTERN CONUS, FRI-MON,
OCT 2-5.
SLIGHT RISK OF HIGH WINDS FOR PARTS OF THE CALIFORNIA AND SOUTHWESTERN OREGON
COAST, FRI-SUN, OCT 2-4.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF SOUTHERN MAINLAND ALASKA, AND
SOUTHEAST ALASKA, FRI-MON, OCT 2-5.
SLIGHT RISK OF HIGH WINDS FOR COASTAL PARTS OF SOUTHERN MAINLAND ALASKA, AND
SOUTHEAST ALASKA, FRI-MON, OCT 2-5.
DETAILED SUMMARY
FOR SUNDAY SEPTEMBER 27 - THURSDAY OCTOBER 01:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY OCTOBER 02 - THURSDAY OCTOBER 08: TOWARDS THE MIDDLE OF NEXT WEEK,
BOTH THE GEFS AND ECMWF ENSEMBLES ARE TRENDING TOWARDS FAVORING A STRONGER
SHORTWAVE TROUGH DIGGING INTO THE FOUR CORNERS AND GREAT PLAINS. BASED ON THE
LATEST ENSEMBLES AND THE OFFICIAL FORECAST FROM THE NATIONAL HURRICANE CENTER
(NHC), HURRICANE POLO IS EXPECTED TO TAKE MORE OF NORTHEAST TRACK ACROSS BAJA
CALIFORNIA AND WESTERN MEXICO UNDER THE INFLUENCE OF THIS MID-LEVEL TROUGH, AND
ADVECT COPIOUS AMOUNTS OF TROPICAL MOISTURE INTO THE CENTRAL CONUS. COMBINED
WITH A FRONTAL BOUNDARY DRAPED FROM THE SOUTHERN HIGH PLAINS INTO THE WESTERN
GREAT LAKES, THERE IS BETTER SUPPORT FOR WIDESPREAD ENHANCED, AND POTENTIALLY
LOCALLY HEAVY PRECIPITATION ALONG THE FRONT BY DAYS 6 AND 7 (SEP 30-OCT 1)
BASED ON QPF FORECASTS FROM THE WEATHER PREDICTION CENTER (WPC). HEADING INTO
THE START OF WEEK-2 (OCT 2), MUCH OF THE TROUGHING IS EXPECTED TO WEAKEN, AS
THERE IS GOOD MODEL AGREEMENT FAVORING RISING MID-LEVEL HEIGHTS ACROSS THE
PLAINS AND MISSISSIPPI VALLEY. HOWEVER, LINGERING FRONTAL ACTIVITY AND
CONTINUED SOUTHERLY FLOW FROM THE GULF LOOKS TO REMAIN A POSSIBLE HAZARD
CONCERN ACROSS MUCH OF THE SOUTHEASTERN CONUS.
THE POTENTIAL FOR A HEAVY PRECIPITATION IS WELL REFLECTED IN THE PROBABILISTIC
EXTREME TOOLS (PETS), WHERE BOTH THE GEFS AND ECMWF MAINTAIN INCREASED CHANCES
(20-30%) FOR 3-DAY AMOUNTS EXCEEDING THE 85TH PERCENTILE AND 1 INCH FROM THE
SOUTHERN PLAINS EASTWARD TO THE LOWER EASTERN SEABOARD EARLY IN THE PERIOD.
GIVEN SUPPORT IN THE UNCALIBRATED PRECIPITATION TOOLS, A SLIGHT RISK OF HEAVY
PRECIPITATION REMAINS POSTED WITH COVERAGE EXPANDED NORTHWARD TO INCLUDE PARTS
OF THE TENNESSEE VALLEY, SOUTHERN APPALACHIANS, LOWER MID-ATLANTIC, AND
ADDITIONAL PORTIONS OF THE SOUTHEAST, VALID THROUGH OCT 5. SOME AREAS OF HEAVY
RAIN INCLUDING POTENTIAL THUNDERSTORMS ARE POSSIBLE IN THESE AREAS, POTENTIALLY
TRIGGERING ISOLATED FLASH FLOODING, ALTHOUGH NO PARTICULAR AREA APPEARS
VULNERABLE TO WIDESPREAD AND PERSISTENT FLOOD CONDITIONS. FURTHER SOUTH, THERE
IS ALSO GROWING SUPPORT IN THE ENSEMBLES FOR SURFACE LOW DEVELOPMENT IN THE
SOUTHWESTERN GULF OF AMERICA, CONSISTENT WITH POTENTIAL TROPICAL CYCLONE (TC)
DEVELOPMENT. WHILE PROBABILISTIC TC GENESIS TOOLS MAINTAIN RELATIVELY LOW ODDS
OF FORMATION LEADING TO MUCH UNCERTAINTY, THESE SIGNALS OVER THE GULF HAVE
GROWN STRONGER IN RECENT DAYS, AND ANY FORMATION AND NORTHWARD TRACK WOULD
PROMPT ADJUSTMENTS TO THE HEAVY PRECIPITATION HAZARD POSTED, AS WELL AS
INCLUDING OTHER CORRESPONDING HAZARDS IN THE UPCOMING OUTLOOKS.
TOWARDS THE MIDDLE OF WEEK-2, RENEWED 500-HPA MEAN TROUGHING IS FAVORED OVER
THE NORTHWESTERN AND NORTHCENTRAL CONUS ASSOCIATED WITH BUILDING HEIGHTS OVER
THE NORTHEASTERN PACIFIC. COMPARED TO THE GEFS, THE ECMWF ENSEMBLE IS MORE
AGGRESSIVE WITH THE RIDGE DEVELOPMENT UPSTREAM, WHICH FORCES A MORE EASTERLY
SOLUTION OF THE MEAN TROUGH OVER THE UPPER MIDWEST WHEREAS THE GEFS FOCUSES
THIS MID-LEVEL FEATURE OVER THE NORTHWESTERN CONUS. UNSEASONABLY COLDER
TEMPERATURES ARE EXPECTED TO ACCOMPANY THE TROUGH, AND RESIDUAL MOISTURE OVER
THE INTERIOR WEST RESULTS IN ACCUMULATING SNOWFALL SIGNALS OVER THE NORTHERN
ROCKIES WHICH IS REFLECTED IN THE GEFS SNOW WATER EQUIVALENT (SWE) PET.
HOWEVER, THE ECMWF IS ABSENT OF ANY SNOW POTENTIAL, AND DUE TO PHASING
DIFFERENCES OF THE TROUGH AND VARIED TEMPERATURE RESPONSES ACROSS THE NORTHERN
TIER, NO CORRESPONDING TEMPERATURE OR SNOW RELATED HAZARDS ARE POSTED.
WITH MEAN SURFACE HIGH (LOW) PRESSURE ESTABLISHED ACROSS THE EASTERN PACIFIC
(CALIFORNIA AND THE GREAT BASIN) EARLY IN WEEK-2, ENSEMBLES CONTINUE TO SHOW
FAIRLY TIGHT MEAN PRESSURE GRADIENTS ALONG THE WEST COAST. THE PREVAILING
OFFSHORE FLOW PATTERN LOOKS TO PROMOTE PERIODS OF ENHANCED WIND SPEEDS OVER
PARTS OF CALIFORNIA AND SOUTHWEST OREGON, AND A SLIGHT RISK OF HIGH WINDS
REMAINS POSTED FOR OCT 2-4. THIS IS SUPPORTED BY THE PETS INDICATING AT LEAST A
20% CHANCE OF WIND SPEEDS EXCEEDING THE 85TH PERCENTILE AND 25 MPH (35 MPH
LOCALLY) AND MODEL ENSEMBLES SHOWING INCREASED CHANCES OF WIND GUSTS EXCEEDING
34 KNOTS (ABOUT 40 MPH) IN THE REGION.
AN AMPLIFYING 500-HPA TROUGH IS FAVORED TO THE SOUTH OF THE ALEUTIANS LATER
NEXT WEEK, WHERE BOTH THE GEFS AND ECMWF FAVOR A MORE WESTWARD SHIFTED TROUGH
AXIS IN THE GULF OF ALASKA IN THE LATEST GUIDANCE. AS A RESULT, THERE ARE
GREATER CHANCES FOR ENHANCED ONSHORE FLOW AND A HEAVY PRECIPITATION RISK ACROSS
COASTAL PORTIONS OF THE SOUTHCENTRAL MAINLAND AND THE SOUTHEAST. BOTH THE GEFS
AND ECMWF PETS ARE IN AGREEMENT DEPICTING AT LEAST 20% CHANCES FOR 3-DAY
AMOUNTS EXCEEDING THE 85TH PERCENTILE WITH POCKETS OF 3 INCHES OVER THIS PART
OF ALASKA. WITH THE UNCALIBRATED ECMWF ALSO FAVORING SLIGHT CHANCES FOR
24-HOUR AMOUNTS EXCEEDING 4 INCHES EARLY IN THE PERIOD, A SLIGHT RISK OF HEAVY
PRECIPITATION IS ISSUED FOR OCT 2-5. IN ADDITION, AN ACCOMPANYING SLIGHT RISK
OF HIGH WINDS ALSO REMAINS POSTED DUE TO THE ENHANCED ONSHORE FLOW REGIME
FAVORED AND THE PETS WHICH ALSO SHOW INCREASED CHANCES FOR WIND SPEEDS
EXCEEDING THE 85TH PERCENTILE AND 40MPH ALONG THE COAST.
FORECASTER: NICK NOVELLA
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