772
FXUS21 KWNC 211856
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST DECEMBER 21 2023
SYNOPSIS: MID-LEVEL LOW PRESSURE OVER THE NORTH PACIFIC IS ANTICIPATED TO PEAK
DURING WEEK-1 AND WEAKEN THROUGHOUT WEEK-2. THIS LOW IS PREDICTED TO SHIFT
FURTHER NORTHWEST TO THE GULF OF ALASKA. HOWEVER, A TRAILING COLD FRONT FROM
THIS LOW EXTENDING TO THE WEST COAST MAY SUPPORT LINGERING HEAVY PRECIPITATION
(HIGH ELEVATION SNOW) AND HIGH WINDS ACROSS THE REGION AND INTERIOR CALIFORNIA
UNTIL THE MIDDLE OF WEEK-2. HIGH WINDS ARE POSSIBLE ACROSS COASTAL PORTIONS OF
SOUTH-CENTRAL AND SOUTHEASTERN ALASKA ASSOCIATED WITH THIS STORM.
HAZARDS
MODERATE RISK FOR HEAVY PRECIPITATION FOR COASTAL AND VALLEY AREAS OF CENTRAL
CALIFORNIA, FRI-TUE, DEC 29-JAN 2.
SLIGHT RISK FOR HEAVY PRECIPITATION FOR PARTS OF CALIFORNIA, FRI-TUE, DEC
29-JAN 2.
SLIGHT RISK FOR HEAVY SNOW FOR THE SIERRA NEVADA, SOUTHERN CASCADES, AND
COASTAL RANGES OF NORTHERN CALIFORNIA, FRI-TUE, DEC 29-JAN 2.
SLIGHT RISK FOR HIGH WINDS FOR COASTAL CALIFORNIA AND SOUTHWESTERN OREGON,
FRI-TUE, DEC 29-JAN 2.
SLIGHT RISK FOR HIGH WINDS ACROSS COASTAL PORTIONS OF SOUTH-CENTRAL AND
SOUTHEASTERN ALASKA, FRI-SUN, DEC 29-31.
DETAILED SUMMARY
FOR SUNDAY DECEMBER 24 - THURSDAY DECEMBER 28:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY DECEMBER 29 - THURSDAY JANUARY 04: THERE CONTINUES TO BE GOOD
AGREEMENT ACROSS MULTIPLE MODEL ENSEMBLE MEANS INDICATING MID-LEVEL TROUGHING
OVER THE NORTH PACIFIC PEAKING WEEK-1 AND WEAKENING THROUGHOUT WEEK-2. THIS
PATTERN FAVORS THE CENTER OF THIS SURFACE LOW SHIFTING FROM NEAR THE WEST COAST
DURING WEEK-1 TO THE GULF OF ALASKA BY WEEK-2. A FRONTAL BOUNDARY EXTENDING
FROM THIS MEAN SURFACE LOW SOUTHWARD TO CALIFORNIA MAY CONTINUE TO BRING
INCREASED CHANCES FOR LINGERING HAZARDOUS PRECIPITATION AND WINDS TO WEST COAST
STATES UNTIL THE MIDDLE OF THE PERIOD. THE WEEK-2 STORMY PATTERN LOOKS MUCH
LESS LIKELY TO BE ASSOCIATED WITH AN ATMOSPHERIC RIVER EVENT, THUS
PROBABILITIES AND HAZARDOUS IMPACTS ARE NOT EXPECTED TO BE AS SIGNIFICANT AS
THOSE DURING WEEK-1. THIS IS EVIDENCED IN THE GEFS AND ECMWF INTEGRATED VAPOR
TRANSPORT (IVT) WHICH SHOWS LOW CHANCES FOR ENHANCED VALUES DURING WEEK-2.
THE SPATIAL COVERAGE FOR THE PRECIPITATION RISKS IS DECREASED IN TODAY’S
OUTLOOK. THE GEFS, ECMWF, AND CANADIAN PROBABILISTIC EXTREMES TOOLS (PETS) SHOW
AT LEAST A 20% CHANCE OF 3-DAY PRECIPITATION EXCEEDING THE 85TH PERCENTILE
CLIMATOLOGICALLY AND ONE INCH (2 INCHES ACROSS NORTHERN CALIFORNIA) ACROSS THE
ENTIRE COAST OF CALIFORNIA. HOWEVER, GIVEN THE ANTICIPATED WEAKENING AND
SHIFTING MID-LEVEL TROUGH ACROSS THE NORTH PACIFIC AND ENSEMBLE MEANS
INDICATING RELATIVELY LOW DAILY PRECIPITATION ACCUMULATIONS, THE SLIGHT RISK
FOR HEAVY PRECIPITATION IS SCOPED TO PARTS OF CALIFORNIA, DEC 29-JAN 2. A
MODERATE RISK IS POSTED WHERE THE ECMWF (GEFS) INDICATES AT LEAST A 40% (30%)
CHANCE OF EXCEEDING THESE THRESHOLDS. A SLIGHT RISK FOR HEAVY SNOW IS
MAINTAINED ACROSS THE SIERRA NEVADA, SOUTHERN CASCADES, AND COASTAL RANGES OF
NORTHERN CALIFORNIA FOR THE SAME PERIOD, WHILE THE MODERATE RISK HAS BEEN
REMOVED IN TODAY’S OUTLOOK DUE TO DECREASING SIGNALS FOR HEAVY PRECIPITATION. A
SLIGHT RISK OF HIGH WINDS IS DESIGNATED FOR COASTAL CALIFORNIA AND SOUTHWESTERN
OREGON WHERE MULTIPLE PETS DEPICT AT LEAST A 20% CHANCE OF EXCEEDING THE 85TH
PERCENTILE AND 25 MPH (40 MPH ACROSS SOUTHWESTERN OREGON AND NORTHERN
CALIFORNIA).
A STRONG SURFACE LOW IS PREDICTED FOR THE GULF OF ALASKA BY THE BEGINNING OF
THE PERIOD. A SLIGHT RISK FOR HIGH WINDS IS POSTED FOR PORTIONS OF
SOUTH-CENTRAL AND SOUTHEASTERN ALASKA, DEC 29-31, WHERE THE PETS INDICATE AT
LEAST A 20% CHANCE OF WIND SPEEDS EXCEEDING THE 85TH PERCENTILE AND 40 MPH.
HIGH WIND SPEEDS ARE ALSO POSSIBLE OVER MARITIME AREAS IN THE GULF OF ALASKA.
THE GREATEST CHANCES FOR HEAVIER PRECIPITATION AMOUNTS ARE FOR SOUTH-CENTRAL
ALASKA. HOWEVER, DUE TO THE PETS LIMITING THE 3-DAY PRECIPITATION TOTALS TO
BELOW 3 INCHES, AN ASSOCIATED HEAVY PRECIPITATION HAZARD IS NOT DESIGNATED AT
THIS TIME.
FORECASTER: MELISSA OU
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