515
FXUS21 KWNC 091919
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST DECEMBER 09 2024
SYNOPSIS: AMPLIFIED MID-LEVEL LOW PRESSURE IS PREDICTED TO FORM OVER THE
NORTHEASTERN PACIFIC WHICH COULD APPROACH THE WEST COAST BY THE MIDDLE OF
WEEK-2. THIS PATTERN MAY INCREASE CHANCES FOR ATMOSPHERIC RIVER ACTIVITY AND
SUPPORT PERIODIC HEAVY PRECIPITATION, HIGH ELEVATION SNOW, AND HIGH WINDS OVER
PORTIONS OF THE NORTHWESTERN CONTIGUOUS U.S. (CONUS). THIS MID-LEVEL LOW MAY
ALSO SUPPORT A POTENTIALLY STRONG STORM FORMING OVER THE GULF OF ALASKA WHICH
COULD BRING HIGH WINDS TO COASTAL PORTIONS OF SOUTH-CENTRAL AND SOUTHEASTERN
ALASKA DURING WEEK-2.
HAZARDS
SLIGHT RISK OF EPISODIC HIGH WINDS ACROSS PORTIONS OF THE NORTHWESTERN CONUS,
FRI-MON, DEC 19-23.
SLIGHT RISK OF PERIODIC HEAVY PRECIPITATION ACROSS COASTAL PORTIONS OF THE
PACIFIC NORTHWEST AND NORTHERN CALIFORNIA, FRI-MON, DEC 19-23.
SLIGHT RISK OF PERIODIC HEAVY SNOW FOR HIGH ELEVATION PORTIONS OF THE CASCADES,
SIERRA, AND KLAMATH MOUNTAINS, NORTHERN GREAT BASIN, AND NORTHERN ROCKIES,
FRI-MON, DEC 19-23.
SLIGHT RISK OF EPISODIC HIGH WINDS ACROSS PARTS OF SOUTH-CENTRAL AND
SOUTHEASTERN ALASKA, TUE-SAT, DEC 17-21.
DETAILED SUMMARY
FOR THURSDAY DECEMBER 12 - MONDAY DECEMBER 16:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY DECEMBER 17 - MONDAY DECEMBER 23: MULTIPLE MODELS INDICATE
AMPLIFIED MID-LEVEL TROUGHING FORMING OVER THE NORTHEASTERN PACIFIC AT THE
ONSET OF WEEK-2, SHIFTING EASTWARD WITH TIME. THE GEFS AND ECENS INTEGRATED
VAPOR TRANSPORT (IVT) TOOLS INDICATE ENHANCED IVT VALUES (250 KG/M/S) FAVORABLE
FOR ENHANCED ONSHORE MOISTURE AND INCREASED ATMOSPHERIC RIVER ACTIVITY BY THE
MIDDLE OF WEEK-2, ALTHOUGH WITH SOME DIFFERENCES IN TIMING. THE ECENS FAVORS
PEAK VALUES 12/21-12/23 AND THE GEFS FAVORS HEAVIER PRECIPITATION A BIT EARLIER
IN THE PERIOD (12/19-12/21). GIVEN UNCERTAINTY REGARDING TIMING AND PATTERN
EVOLUTION DIFFERENCES, SLIGHT RISKS ARE ISSUED FOR PERIODIC HEAVY PRECIPITATION
ACROSS COASTAL PORTIONS OF THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA, HIGH
ELEVATION HEAVY SNOW FOR PARTS OF THE CASCADES, SIERRA, AND KLAMATH MOUNTAINS,
NORTHERN GREAT BASIN, AND NORTHERN ROCKIES, AND HIGH WINDS ACROSS PORTIONS OF
THE NORTHWESTERN CONUS, DEC 19-23. MULTIPLE PROBABILISTIC EXTREMES TOOLS (PETS)
INDICATE AT LEAST A 20% CHANCE OF 3-DAY LIQUID EQUIVALENT TOTALS EXCEEDING THE
85TH PERCENTILE CLIMATOLOGICALLY AND 2 INCHES ACROSS THE PACIFIC NORTHWEST AND
NORTHERN CALIFORNIA. THE SNOW HAZARD IS BASED ON UNCALIBRATED ECENS GUIDANCE
AND RECENT DETERMINISTIC MODEL SOLUTIONS. FOR WINDS, THE PETS SHOW AT LEAST A
20% CHANCE OF WIND SPEEDS EXCEEDING THE 85TH PERCENTILE AND 40 MPH ACROSS
COASTAL PORTIONS OF THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA. THE RISK OF
HIGH WINDS ACROSS THE NORTHERN GREAT BASIN, NORTHERN ROCKIES, AND HIGH PLAINS
ARE ATTRIBUTED TO A TIGHT PRESSURE GRADIENT ANTICIPATED WITH SURFACE LOW
PRESSURE TRACKING ACROSS THE NORTHERN PLAINS WITH ADJACENT SURFACE HIGH
PRESSURE OVER THE GREAT BASIN.
THE MID-LEVEL TROUGH IN THE NORTHEAST PACIFIC MAY SUPPORT DEVELOPMENT OF A
STRONG STORM CENTERED OVER THE GULF OF ALASKA. A SLIGHT RISK OF EPISODIC HIGH
WINDS IS DESIGNATED FOR COASTAL PORTIONS OF SOUTH-CENTRAL AND SOUTHEASTERN
ALASKA, DEC 17-21, WHERE THE PETS INDICATE AT LEAST A 20% CHANCE OF WIND SPEEDS
EXCEEDING THE 85TH PERCENTILE AND 40 MPH. THIS STORM IS ALSO ANTICIPATED TO
BRING ENHANCED PRECIPITATION TO THESE AREAS, ALTHOUGH THE PETS DO NOT YET
SUPPORT TOTALS REACHING HAZARD CRITERIA AT THIS TIME.
FORECASTER: MELISSA OU
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