744
FXUS21 KWNC 222009
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST NOVEMBER 22 2023
SYNOPSIS: THERE CONTINUES TO BE GOOD MODEL CONSENSUS INDICATING A STRONG
SURFACE LOW PRESSURE MOVING FROM THE BERING SEA TO THE GULF OF ALASKA DURING
WEEK-2. THIS PATTERN IS ANTICIPATED TO SUPPORT INCREASED CHANCES FOR HIGH WINDS
INITIALLY TO THE ALEUTIANS SHIFTING TO THE SOUTHERN COAST IN ADDITION TO
ENHANCED PRECIPITATION ACROSS THE KENAI PENINSULA AND SOUTHEASTERN ALASKA. AS
THIS STORM TRACKS SOUTHWARD, HEAVY PRECIPITATION AND HIGH WINDS MAY IMPACT
COASTAL PORTIONS OF THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA TOWARDS THE
END OF THE PERIOD.
HAZARDS
SLIGHT RISK FOR HIGH WINDS FOR MUCH OF SOUTHERN ALASKA, FROM BRISTOL BAY
EASTWARD AND SOUTHWARD TO INCLUDE ALL OF THE SOUTHERN COAST AND SOUTHEAST
ALASKA, THU-MON, NOV 30-DEC 4.
SLIGHT RISK OF HEAVY PRECIPITATION FOR COASTAL PORTIONS OF THE PACIFIC
NORTHWEST AND NORTHERN AND CENTRAL CALIFORNIA, SUN-TUE, DEC 3-5.
SLIGHT RISK OF HIGH WINDS FOR COASTAL PORTIONS OF THE PACIFIC NORTHWEST AND
NORTHERN AND CENTRAL CALIFORNIA, FRI-TUE, DEC 1-5.
DETAILED SUMMARY
FOR SATURDAY NOVEMBER 25 - WEDNESDAY NOVEMBER 29:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY NOVEMBER 30 - WEDNESDAY DECEMBER 06: THERE CONTINUES TO BE
MULTI-MODEL ENSEMBLE MEAN DEPICTION OF AMPLIFIED MID-LEVEL TROUGHING DEVELOPING
OVER THE BERING SEA BY THE ONSET OF WEEK-2, SHIFTING TO THE GULF OF ALASKA BY
THE MIDDLE OF THE PERIOD. THE AMPLITUDE OF THIS TROUGH IS NOTICEABLY GREATER IN
TODAY’S GUIDANCE, EXTENDING FURTHER SOUTHWARD COMPARED TO YESTERDAY,
TRANSLATING TO INCREASING SIGNALS FOR HAZARDOUS WIND AND PRECIPITATION ACROSS
PARTS OF THE WEST COAST.
AMPLIFIED MID-LEVEL TROUGHING IN THE NORTHEAST PACIFIC SUPPORTS A STRONG STORM
FORMING OVER THE BERING SEA AT THE BEGINNING OF THE PERIOD TRACKING TO THE GULF
OF ALASKA DURING WEEK-2. A SLIGHT RISK FOR HIGH WINDS IS MAINTAINED ACROSS A
BROAD AREA OF SOUTHERN COASTAL ALASKA, EXTENDING FROM BRISTOL BAY EASTWARD AND
SOUTHWARD TO THE SOUTHERN COAST AND SOUTHEAST ALASKA, NOV 30 TO DEC 4. ECMWF
AND GEFS PROBABILISTIC EXTREMES TOOLS (PETS) BOTH INDICATE AT LEAST A 20%
CHANCE OF WIND SPEEDS EXCEEDING THE 85TH PERCENTILE AND 40 MPH, WITH ENSEMBLE
SOLUTIONS FOR SURFACE LOW PRESSURE INDICATING A STRONG PRESSURE GRADIENT
DIRECTING ONSHORE FLOW INTO THE SOUTHERN COAST. THIS STORM MAY ALSO SUPPORT
INCREASED CHANCES FOR LOCALIZED HEAVY PRECIPITATION ACROSS SOUTHEAST ALASKA.
RECENT DETERMINISTIC GFS SOLUTIONS SHOW THE POTENTIAL FOR LOCAL AREAS EXCEEDING
3 INCHES IN A 24-HOUR PERIOD. THE GEFS AND ECMWF PETS CONTINUE TO INDICATE AT
LEAST A 20% PROBABILITY OF 3-DAY PRECIPITATION EXCEEDING THE 85TH PERCENTILE
CLIMATOLOGICALLY AND 2 INCHES IN A 3-DAY PERIOD BUT REMAIN BELOW 3 INCHES. DUE
TO PRECIPITATION TOTALS FROM ENSEMBLE SOLUTIONS AND THE PETS NOT EXCEEDING
HAZARD THRESHOLDS, NO ASSOCIATED PRECIPITATION HAZARD IS POSTED AT THIS TIME.
HOWEVER, LANDSLIDES HAVE BEEN RECENTLY REPORTED IN THE ALASKA PANHANDLE AND
HIGH WINDS WEAKENING TREE ROOTS COUPLED WITH ENHANCED PRECIPITATION FURTHER
SATURATING SOILS HAS THE POTENTIAL TO CONTINUE THE INCREASED THREAT FOR
LANDSLIDES.
AS THIS STORM SHIFTS SOUTHWARD, THERE IS INCREASED POTENTIAL FOR HEAVY
PRECIPITATION AND HIGH WINDS. DUE TO MULTIPLE MODELS INDICATING STRONGER
MID-LEVEL AMPLIFIED TROUGHING SINKING FURTHER SOUTHWARD COMPARED TO YESTERDAY,
THERE ARE INCREASING SIGNALS FOR STORM IMPACTS ACROSS PARTS OF THE WEST COAST.
GEFS AND ECMWF ARE INDICATING ENHANCED INTEGRATED VAPOR TRANSPORT (IVT) VALUES
(>250 KG/M/S) EXTENDING FROM THE PACIFIC NORTHWEST TO CENTRAL CALIFORNIA BY THE
MIDDLE OF WEEK-2. A SLIGHT RISK OF HEAVY PRECIPITATION IS DESIGNATED FOR
COASTAL PORTIONS OF THE PACIFIC NORTHWEST EXTENDING SOUTHWARD TO SAN FRANCISCO,
DEC 3-5, WHERE AND WHEN THE GEFS, ECMWF, AND CANADIAN PETS INDICATE AT LEAST A
20% CHANCE OF 3-DAY PRECIPITATION EXCEEDING THE 85TH PERCENTILE AND 2 INCHES.
THERE IS POTENTIAL FOR PORTIONS OF THE CASCADES TO RECEIVE HEAVY SNOW WHICH
COULD MAKE TRAVEL CONDITIONS HAZARDOUS. HOWEVER DUE TO HIGH UNCERTAINTY
REGARDING ANTICIPATED SNOWFALL AMOUNTS, A RELATED SNOW HAZARD IS NOT DESIGNATED
AT THIS TIME. A SLIGHT RISK OF HIGH WINDS IS ALSO DESIGNATED FOR COASTAL
PORTIONS OF THE PACIFIC NORTHWEST AND NORTHERN AND CENTRAL CALIFORNIA, DEC 1-5
ASSOCIATED WITH THIS STORM. THE GEFS, ECMWF, AND CANADIAN PETS INDICATE AT
LEAST A 20% CHANCE OF WIND SPEEDS EXCEEDING THE 85TH PERCENTILE AND 40 MPH IN
SOME OF THE HIGHLIGHTED RISK AREAS.
A SURFACE LOW PREDICTED TO FORM OVER THE SOUTHWEST INCREASES THE CHANCES FOR
LOCALIZED ENHANCED SNOWFALL ACROSS PARTS OF THE FOUR CORNERS AT THE BEGINNING
OF WEEK-2. THE GEFS SNOW EQUIVALENT PET SHOWS AT LEAST A 20% CHANCE OF 3-DAY
SNOWFALL EXCEEDING THE 85TH PERCENTILE AND HALF AN INCH AT THE BEGINNING OF THE
PERIOD (NOV 30-DEC 2). AT THIS TIME NO ASSOCIATED SNOW HAZARDS ARE POSTED DUE
TO HIGH UNCERTAINTY REGARDING THE SPATIAL EXTENT AND SNOWFALL TOTALS.
MULTIPLE MODELS SHOW THE POSSIBILITY OF A FRONT EXTENDING SOUTHWARD FROM A
SURFACE LOW OVER CENTRAL CANADA INTO THE SOUTHERN PLAINS AT THE BEGINNING OF
THE PERIOD. THE GREATEST LIKELIHOOD FOR HEAVY PRECIPITATION IS ACROSS THE LOWER
MISSISSIPPI VALLEY, WHERE THE GEFS AND CANADIAN PETS SHOW AT LEAST A 20% CHANCE
OF 3-DAY RAINFALL EXCEEDING THE 85TH PERCENTILE AND ONE INCH, DAYS 10-12 (DEC
2-4) FURTHER INDICATED BY MULTIPLE MODEL ENSEMBLE MEANS. DUE TO HIGH
UNCERTAINTY REGARDING THE TIMING AND PRECIPITATION TOTALS, NO RELATED HAZARD IS
POSTED AT THIS TIME.
FORECASTER: MELISSA OU
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