878
FXUS21 KWNC 191909
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST DECEMBER 19 2025
SYNOPSIS: FOLLOWING A SOUTHWARD SHIFT IN THE STORM TRACK ALONG THE WEST COAST,
MID-LEVEL LOW PRESSURE OVER THE NORTHEASTERN PACIFIC INCREASES THE RISK FOR
ADDITIONAL HEAVY PRECIPITATION, HEAVY SNOW, AND HIGH WINDS ACROSS THE PACIFIC
NORTHWEST TO CLOSE OUT 2025 AND HEADING INTO THE NEW YEAR. THE ENHANCED PACIFIC
FLOW FAVORS HEAVY SNOW ACROSS THE NORTHERN ROCKIES AND AN ELEVATED CHANCE OF
HIGH WINDS OVER MUCH OF THE WESTERN AND CENTRAL U.S. STRONG MID-LEVEL HIGH
PRESSURE OVER THE BERING SEA IS LIKELY TO PROMOTE PERSISTENT ARCTIC HIGH
PRESSURE AND ANOMALOUSLY COLD TEMPERATURES FOR ALASKA.
HAZARDS
HIGH RISK OF HEAVY PRECIPITATION FOR WESTERN WASHINGTON, SAT-MON, DEC 27-29.
HIGH RISK OF HEAVY SNOW FOR THE NORTHERN CASCADES, SAT-MON, DEC 27-29.
MODERATE RISK OF HEAVY PRECIPITATION FOR THE PACIFIC NORTHWEST AND NORTHERN
CALIFORNIA, SAT-FRI, DEC 27-JAN 2.
MODERATE RISK OF HEAVY SNOW FOR THE CASCADES AND KLAMATH MOUNTAINS, SAT-FRI,
DEC 27-JAN 2.
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE PACIFIC NORTHWEST AND NORTHERN
CALIFORNIA, SAT-FRI, DEC 27-JAN 2.
SLIGHT RISK OF HEAVY SNOW FOR THE CASCADES, KLAMATH, AND THE NORTHERN SIERRA
NEVADA MOUNTAINS, SAT-FRI, DEC 27- JAN 2.
MODERATE RISK OF HEAVY SNOW FOR THE NORTHERN ROCKIES AND NORTHERN INTERMOUNTAIN
WEST, SAT-FRI, DEC 27-JAN 2.
SLIGHT RISK OF HEAVY SNOW FOR THE CENTRAL AND NORTHERN ROCKIES, PARTS OF THE
GREAT BASIN AND NORTHERN INTERMOUNTAIN WEST, SAT-FRI, DEC 27-JAN 2.
SLIGHT RISK OF HEAVY SNOW FOR SOUTHWESTERN COLORADO, SAT-SUN, DEC 27-28.
MODERATE RISK OF HIGH WINDS FOR PARTS OF THE WEST, SAT-FRI, DEC 27-JAN 2.
SLIGHT RISK OF HIGH WINDS FOR MUCH OF THE WEST, GREAT PLAINS, AND UPPER
MISSISSIPPI VALLEY, SAT-FRI, DEC 27-JAN 2.
MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR MUCH OF SOUTHERN MAINLAND
AND SOUTHEAST ALASKA, SAT-TUE, DEC 27-30.
SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR SOUTHERN AND CENTRAL MAINLAND
AND SOUTHEAST ALASKA, SAT-THU, DEC 27-JAN 2.
SLIGHT RISK OF HIGH WINDS FOR MUCH OF SOUTHERN ALASKA, INCLUDING THE ALASKA
RANGE, SAT-THU, DEC 26-JAN 2.
FLOODING POSSIBLE FOR PARTS OF NORTHERN CALIFORNIA AND THE PACIFIC NORTHWEST.
DETAILED SUMMARY
FOR MONDAY DECEMBER 22 - FRIDAY DECEMBER 26:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY DECEMBER 27 - FRIDAY JANUARY 02: THE ECENS, GEFS, AND CMCE ARE IN
GOOD AGREEMENT AND CONTINUE TO HAVE GOOD RUN TO RUN CONSISTENCY INDICATING AN
ANOMALOUS 500-HPA RIDGE (TROUGH) PERSISTING OVER THE BERING SEA (NORTHEASTERN
PACIFIC) THROUGHOUT WEEK-2. THE AMPLIFIED NORTHEASTERN PACIFIC TROUGH FAVORS A
RETURN OF AN ATMOSPHERIC RIVER (AR) TO THE PACIFIC NORTHWEST, ESPECIALLY
WESTERN WASHINGTON. EARLY IN WEEK-2, THE ECENS DEPICTS LARGE PROBABILITIES (>
60% CHANCE) FOR INTEGRATED VAPOR TRANSPORT (IVT) VALUES REACHING 250 KG/M/S
BETWEEN 45-50 DEGREES N. THE PREFERRED UNCALIBRATED ECENS FEATURES GREATER THAN
A 70 PERCENT CHANCE OF 3-DAY PRECIPITATION AMOUNTS EXCEEDING 2 INCHES ACROSS
NORTHWESTERN WASHINGTON. BASED ON THE GOOD AGREEMENT AND CONTINUITY REGARDING
TIMING FROM THE ECENS AND GEFS MODEL SOLUTIONS, A HIGH RISK (> 60% CHANCE) OF
HEAVY PRECIPITATION IS DESIGNATED FOR WESTERN WASHINGTON FROM DECEMBER 27-29.
THE PERSISTENT LONGWAVE PATTERN OVER THE NORTH PACIFIC ALONG WITH SUPPORT FROM
THE ECENS IVT TOOL AND UNCALIBRATED 1 TO 3-DAY PRECIPITATION FORECASTS FROM THE
ECENS AND GEFS WARRANT A MODERATE RISK (40-60% CHANCE) OF HEAVY PRECIPITATION
FROM COASTAL WASHINGTON AND OREGON EAST TO THE CASCADES ALONG WITH NORTHWESTERN
CALIFORNIA FOR THE ENTIRETY OF WEEK-2. BASED ON THE ECENS AND GEFS
PROBABILISTIC EXTREMES TOOLS (PETS), A SLIGHT RISK (20-40% CHANCE) OF HEAVY
PRECIPITATION EXTENDS SOUTH TO INCLUDE THE NORTHERN SIERRA NEVADA MOUNTAINS AND
IS ALSO VALID THROUGH THE END OF WEEK-2, JANUARY 2ND. GIVEN THE ONGOING RIVER
FLOODING AND SATURATED SOILS ALONG WITH HEAVY PRECIPITATION FORECAST IN THE
NEXT WEEK, A POSSIBLE FLOODING HAZARD, WITH AN ASSOCIATED RISK OF LANDSLIDES
AND DEBRIS FLOWS IN STEEP TERRAIN OR BURN SCARS, REMAINS POSTED FOR PARTS OF
THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA. SINCE THE HEAVIEST PRECIPITATION
IS FORECAST TO END ACROSS CENTRAL AND SOUTHERN CALIFORNIA BY THE START OF
WEEK-2 (DECEMBER 27), HEAVY PRECIPITATION AND FLOODING HAZARDS WERE
DISCONTINUED SOUTH OF THE BAY AREA.
THE ENHANCED PACIFIC MOISTURE IS FAVORED TO OVERSPREAD THE INTERIOR WEST,
LEADING TO AN ELEVATED RISK OF HEAVY SNOW FOR PARTS OF THE NORTHERN ROCKIES,
GREAT BASIN, AND NORTHERN INTERMOUNTAIN WEST. THIS CONTINUES TO BE SUPPORTED BY
BOTH THE PRECIPITATION AND SNOW WATER EQUIVALENT PETS, AS WELL AS THE RAW SNOW
TOOLS FROM THE GEFS AND ECMWF. A MODERATE RISK OF HEAVY SNOW REMAINS POSTED
FOR THE NORTHERN ROCKIES FOR THE ENTIRETY OF WEEK-2 WHERE SIGNALS FOR AMOUNTS
EXCEEDING A FOOT ARE THE GREATEST IN THE TOOLS. A BROADER AREA IS HIGHLIGHTED
WITH A SLIGHT RISK OF HEAVY SNOW EXTENDING SOUTH TO NORTHEASTERN UTAH AND
NORTHWESTERN COLORADO. ON DECEMBER 27 AND 28, A SHORTWAVE TROUGH IS FORECAST TO
CROSS THE FOUR CORNERS REGION SUPPORTING A SLIGHT RISK OF HEAVY SNOW FOR
SOUTHWESTERN COLORADO.
THE DETERMINISTIC 0Z AND 12Z ECMWF MODEL SHOWS A CLOSED 500-HPA LOW OVER ALASKA
WITH A BUILDING 500-HPA RIDGE ALONG THE WEST COAST AND THUS A PERIOD OF MUCH
DRIER WEATHER FOR MOST OF THE WEST, BEGINNING ON DECEMBER 27. IN ADDITION,
AROUND A QUARTER OF THE ECMWF ENSEMBLE MEMBERS FAVOR THIS DRIER SOLUTION. THE
WEEK-2 HAZARDS LEANED ON GUIDANCE FROM THE MULTI-MODEL ENSEMBLE MEANS, BUT
MODEL TRENDS FOR THE LONGWAVE PATTERN ALONG THE WEST COAST WILL BE CLOSELY
MONITORED IN SUBSEQUENT OUTLOOKS.
ACCOMPANYING THE HEAVY PRECIPITATION AND HEAVY SNOW RISKS, THE LONGWAVE PATTERN
AND ENHANCED PACIFIC FLOW SUPPORT PERIODS OF HIGH WINDS THROUGHOUT WEEK-2. A
MODERATE RISK FOR HIGH WINDS IS DESIGNATED FROM THE COASTAL PACIFIC NORTHWEST
AND NORTHERN CALIFORNIA EAST TO THE NORTHERN AND CENTRAL ROCKIES, INCLUDING THE
COLORADO FRONT RANGE. FARTHER EAST, INDIVIDUAL SHORTWAVES ARE ANTICIPATED TO
PERIODICALLY BE EJECTED EASTWARD, INDUCING ONE OR MORE SURFACE LOWS DEVELOPING
OVER THE GREAT PLAINS. THEREFORE, A SLIGHT RISK OF HIGH WINDS IS POSTED FOR
MUCH OF THE WEST, GREAT PLAINS, AND UPPER MISSISSIPPI VALLEY.
ARCTIC HIGH PRESSURE IS LIKELY TO PERSIST OVER ALASKA WITH THE MULTI-MODEL
ENSEMBLE MEAN SOLUTIONS FAVORING ANOMALOUS COLD PEAKING EARLY IN WEEK-2. BASED
ON THE ECENS AND GEFS PETS INDICATING AT LEAST A 40 PERCENT CHANCE OF
TEMPERATURES FALLING BELOW THE 15TH PERCENTILE, A MODERATE RISK OF MUCH BELOW
NORMAL TEMPERATURES REMAINS POSTED FOR SOUTHERN MAINLAND ALASKA, SOUTHEASTERN
ALASKA, AND THE ALEUTIANS FROM DECEMBER 27 TO 30. THE SLIGHT RISK IS VALID
THROUGH THE ENTIRETY OF WEEK-2 AND INCLUDES ALL OF ALASKA SOUTH OF THE BROOKS
RANGE. GUSTY, NORTHERLY WINDS MAY ACCOMPANY THE SURGES OF ARCTIC AIR,
SUPPORTING A SLIGHT RISK OF HIGH WINDS FOR THE ALEUTIANS AND SOUTHERN ALASKA.
THE VERY COLD WEATHER AND HIGH WINDS ALONG THE SOUTHERN TIER OF THE STATE
INCREASES THE THREAT FOR HEAVY FREEZING SPRAY AT TIMES NEAR LARGER BODIES OF
WATER.
FORECASTER: BRAD PUGH
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