324
FXUS21 KWNC 231944
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST DECEMBER 23 2025
SYNOPSIS: AN EVOLVING MID-LEVEL PATTERN IS FORECAST HEADING INTO THE NEW YEAR,
WITH MID-LEVEL LOW PRESSURE EXPECTED TO BRING INCREASED CHANCES FOR ENHANCED
ONSHORE FLOW AND UNSETTLED CONDITIONS OVER THE SOUTHWESTERN CONTIGUOUS U.S.
(CONUS) EARLY IN WEEK-2. THEREAFTER, MID-LEVEL LOW PRESSURE IS EXPECTED TO
DEVELOP FURTHER NORTH ACROSS THE NORTHEASTERN PACIFIC, BRINGING A RENEWED RISK
OF ATMOSPHERIC RIVER (AR) RELATED HAZARDS ACROSS THE NORTHWESTERN CONUS LATER
IN WEEK-2. STRONG MID-LEVEL HIGH PRESSURE OVER THE BERING SEA IS LIKELY TO
PROMOTE PERSISTENT ARCTIC HIGH PRESSURE AND ANOMALOUSLY COLD TEMPERATURES FOR
MANY PARTS OF ALASKA. AN ENHANCED RISK OF HIGH WINDS REMAINS FOR MUCH OF THE
NORTHEASTERN CONUS ASSOCIATED WITH AN AREA OF MID-LEVEL AND SURFACE LOW
PRESSURE.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE SOUTHERN CALIFORNIA, AND
THE DESERT SOUTHWEST, WED-FRI, DEC 31-JAN 2
SLIGHT RISK OF HEAVY SNOW FOR THE HIGHER ELEVATIONS OF THE SOUTHERN SIERRA
NEVADA MOUNTAINS AND LOWER FOUR CORNERS, WED-FRI, DEC 31-JAN 2.
SLIGHT RISK OF HIGH WINDS OVER THE SOUTHWESTERN CONUS, WED-FRI, DEC 31-JAN 2.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF NORTHERN CALIFORNIA AND THE
PACIFIC NORTHWEST, THU-TUE, JAN 1-6.
SLIGHT RISK OF HEAVY SNOW FOR THE HIGHER ELEVATIONS OF NORTHERN SIERRA NEVADA,
KLAMATH, AND CASCADES, THU-TUE, JAN 1-6.
SLIGHT RISK OF HEAVY SNOW FOR PORTIONS OF THE HIGHER ELEVATIONS OF THE NORTHERN
INTERMOUNTAIN, GREAT BASIN, AND ROCKIES, THU-TUE, JAN 1-6.
SLIGHT RISK OF HIGH WINDS FOR THE PORTIONS OF THE NORTHEASTERN CONUS, WED-THU,
DEC 31-JAN1.
MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF CENTRAL AND
SOUTHERN MAINLAND ALASKA AND SOUTHEAST ALASKA, FRI-TUE, JAN 2-6.
SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR SOUTHERN AND CENTRAL MAINLAND
AND SOUTHEAST ALASKA, WED-TUE, DEC 31-JAN 6.
SLIGHT RISK OF HIGH WINDS FOR MUCH OF SOUTHERN ALASKA, INCLUDING THE ALASKA
RANGE, WED-TUE, DEC 31-JAN 6.
DETAILED SUMMARY
FOR FRIDAY DECEMBER 26 - TUESDAY DECEMBER 30:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY DECEMBER 31 - TUESDAY JANUARY 06: THERE CONTINUES TO BE GOOD
AGREEMENT IN THE MEAN 500-HPA WEEK-2 HEIGHT ANOMALY FORECASTS AMONG THE
DYNAMICAL MODELS FEATURING A HIGHLY AMPLIFIED RIDGE OVER THE BERING STRAIT WITH
DOWNSTREAM TROUGHING OVER THE NORTHEASTERN PACIFIC. CONSISTENT WITH PREVIOUS
THINKING, THIS PATTERN REMAINS FAVORABLE FOR THE ADVECTION OF VERY COLD ARCTIC
AIR INTO ALASKA, AS WELL AS THE THREAT OF ATMOSPHERIC RIVER (AR) ACTIVITY OVER
THE WEST COAST OF THE U.S DURING WEEK-2. OVER THE PAST FEW DAYS, HOWEVER, BOTH
THE GEFS AND ECMWF HAVE BEGUN TO HEAVILY TREND TOWARDS BUILDING MID-LEVEL
POSITIVE HEIGHTS OVER THE NORTHWESTERN CONUS TOWARDS THE MIDDLE OF NEXT WEEK,
WHERE THE BRIDGING BETWEEN TWO RIDGE ANOMALY CENTERS LOCATED OVER THE NORTHERN
PACIFIC AND CENTRAL CONUS LOOKS TO FORCE A MEAN CUTOFF LOW FEATURE OFFSHORE OF
BAJA CALIFORNIA. AS A RESULT, MUCH OF THE ENHANCED ONSHORE FLOW OVER THE
NORTHERN HALF OF THE WEST COAST IS FAVORED TO RELAX, WITH UNSETTLED WEATHER
BECOMING MORE FOCUSED FURTHER SOUTH OVER THE SOUTHWESTERN CONUS HEADING INTO
THE NEW YEAR. THIS PATTERN SHIFT LOOKS TO BE TEMPORARY AS ENSEMBLES FAVOR A
RELOADING NORTHEASTERN PACIFIC 500-HPA TROUGH, POINTING TO THE RETURN OF AN
ENHANCED ONSHORE FLOW REGIME OVER THE NORTHWESTERN CONUS LATER IN WEEK-2.
DESPITE BEING SHORT-LIVED, SUCH A REPRIEVE FROM THE AR-RELATED HAZARDS OVER THE
NORTHERN HALF OF THE WEST COAST WOULD BE WELCOMED, AS ANY DRIER THAN NORMAL
CONDITIONS WOULD HELP MITIGATE FLOOD RISKS AND ALLOW SOME RECOVERY OF SATURATED
CONDITIONS OVER THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA FOLLOWING VERY
WET CONDITIONS BEING REGISTERED THIS MONTH.
BOTH THE GEFS AND ECMWF BASED INTEGRATED VAPOR TRANSPORT (IVT) TOOLS ARE IN
AGREEMENT REFLECTING THIS PATTERN EVOLUTION, FAVORING THE HIGHEST IVT SIGNALS
SOUTH OF 35N TIED TO THE MEAN CUTOFF FEATURE EARLY IN WEEK-2 BEFORE THE SIGNALS
REEMERGE FURTHER NORTH DURING THE SECOND HALF OF THE PERIOD. LIKEWISE,
PROBABILISTIC EXTREME TOOLS (PETS) FEATURE 40-50% CHANCES FOR 3-DAY
PRECIPITATION AMOUNTS EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE FROM
SOUTHERN CALIFORNIA TO THE LOWER FOUR CORNERS. WHILE THESE SIGNALS ARE
SUPPORTIVE OF A MODERATE RISK DESIGNATION OF HEAVY PRECIPITATION AND HIGH
ELEVATION HEAVY SNOW, BOTH THE UNCALIBRATED GEFS AND ECMWF ARE COMPARABLY
DRIER, DEPICTING GENERALLY 20% CHANCES OF 3-DAY AMOUNTS EXCEEDING AN INCH. DUE
TO BETTER SKILL OF THE UNCALIBRATED PRECIPITATION GUIDANCE OVER THIS PART OF
THE COUNTRY DURING THE PAST 30 DAYS, ONLY SLIGHT RISKS OF HEAVY PRECIPITATION
AND HIGH ELEVATION SNOW ARE POSTED AND ARE VALID FOR THROUGH JAN 2 BEFORE THE
MID-LEVEL FLOW BECOMES MORE ZONAL. ELEVATED WIND SPEEDS ARE ALSO LIKELY AT THE
BASE AND AHEAD OF THE MEAN CUTOFF FEATURE ALOFT, THUS A SLIGHT RISK OF HIGH
WINDS IS ALSO POSTED OVER A BROAD PORTION OF THE SOUTHWESTERN CONUS FOR THE
SAME PERIOD.
BY DAYS 9 AND 10 (JAN 1-2), DAILY RAW TOOLS SHOW THE RETURN OF INCREASING
PRECIPITATION AMOUNTS OVER THE PACIFIC NORTHWEST, AS 500-HPA TROUGHING
REESTABLISHES ITSELF OVER THE NORTHEASTERN PACIFIC. BY COMPARISON, THE
ANOMALOUS TROUGHING IS STRONGEST IN THE GEFS AND CANADIAN, WITH ALL MODELS
SHOWING THIS MID-LEVEL FEATURE PEAKING IN AMPLITUDE BY DAY 12 (JAN 4). A SLIGHT
RISK OF HEAVY PRECIPITATION IS POSTED OVER NORTHERN CALIFORNIA AND THE PACIFIC
NORTHWEST WHERE PETS SHOW 20-30% CHANCES FOR 3-DAY AMOUNTS EXCEEDING THE 85TH
PERCENTILE FOR JAN 1-6. BASED ON THE SNOW WATER EQUIVALENT (SWE) PET FROM THE
GEFS, AND RAW SNOW TOOLS, A SLIGHT RISK OF HEAVY SNOW IS ALSO ISSUED FOR THE
HIGHER ELEVATIONS OF THE WEST COAST, AS WELL AS, SLIGHT RISKS OF HEAVY SNOW AND
HIGH WINDS (JAN 1-6) OVER THE PARTS OF THE INTERIOR WEST DUE TO THE ANOMALOUS
TROUGHING AND ACCOMPANYING ENHANCED MOISTURE FAVORED TO SHIFT FURTHER INLAND
WITH TIME. CORRESPONDING MODERATE RISK AREAS WERE CONSIDERED FOR INCLUSION,
THOUGH THE RAW TOOLS, CALIBRATED PETS, AND IVT TOOLS ARE NOT QUITE ROBUST
ENOUGH WITH THE PRECIPITATION AND ENHANCED MOISTURE SIGNALS, WHICH PRECLUDES A
HIGHER RISK DESIGNATION AT THIS TIME. THE ADDITION OF MODERATE RISK AREAS WILL
BE REVISITED IN UPCOMING HAZARD OUTLOOKS SHOULD THERE BE STRONGER SUPPORT IN
THE PROBABILISTIC GUIDANCE AS WELL AS BETTER RUN-TO-RUN CONTINUITY WITH THE
TRANSITION FROM ANOMALOUS RIDGING TO TROUGHING OVER THE WESTERN CONUS. THE
POSSIBLE FLOODING HAZARD IS REMOVED IN THE UPDATED OUTLOOK DUE TO A REDUCTION
IN FLOODING RESPONSES IN THE WATER MODELS THROUGH EARLY JANUARY, HOWEVER
ADDITIONAL FLOODING OVER PARTS OF THE WEST COAST CANNOT BE RULED OUT DURING
WEEK-2.
EAST OF THE ROCKIES, POTENTIALLY STRONG TROUGHING DOWNSTREAM OF THE RIDGE
ANOMALY CENTER FAVORED OVER THE CENTRAL CONUS SUPPORTS AN INCREASED RISK OF
HIGH WINDS OVER THE NORTHEASTERN CONUS EARLY IN WEEK-2. MEAN SURFACE LOW
PRESSURE REMAINS FAVORED OVER SOUTHEASTERN CANADA, WHERE RAW ENSEMBLES SHOW
MORE OF A STRONGER GRADIENT FURTHER WEST INTO THE UPPER MIDWEST. THEREFORE, A
SLIGHT RISK OF HIGH WINDS REMAINS POSTED OVER THE NORTHEASTERN AND IS EXPANDED
WESTWARD INTO THE UPPER MISSISSIPPI VALLEY, AND VALID THROUGH JAN 1. DUE TO
MORE RIDGING FAVORED OVER THE NORTHWESTERN CONUS EARLY IN THE PERIOD, THERE ARE
HIGHER CHANCES FOR NEAR-NORMAL TEMPERATURES EAST OF THE MISSISSIPPI. WHILE THE
ECMWF PET SHOWS INCREASED CHANCES FOR MINIMUM TEMPERATURES FALLING BELOW THE
15TH PERCENTILE, THE GEFS PET IS LESS SUPPORTIVE OF THIS RISK RESULTING IN NO
CORRESPONDING TEMPERATURE HAZARDS.
ARCTIC HIGH PRESSURE REMAINS FAVORED TO PERSIST OVER ALASKA DURING WEEK-2. A
BRIEF EASING OF THE ANOMALOUS COLD IS EXPECTED THROUGH JAN 1, BEFORE BUILDING
BACK AGAIN BY JANUARY 2 ASSOCIATED WITH THE RELOADING TROUGHING DOWNSTREAM OF
THE POTENT RIDGE . THEREFORE A MODERATE RISK IS DESIGNATED FOR THESE DATES FOR
MUCH OF SOUTHERN MAINLAND AND SOUTHEAST ALASKA. THE SLIGHT RISK GOES THROUGH
THE ENTIRETY OF WEEK-2 AND INCLUDES ALL OF ALASKA SOUTH OF THE BROOKS RANGE.
WITH HIGH PRESSURE OVER THE YUKON AND SURFACE LOW PRESSURE OVER THE GULF OF
ALASKA, A TIGHT PRESSURE GRADIENT MAY LEAD TO HIGH WINDS (GAP WINDS FOR THE
SOUTHEASTERN MAINLAND AND SOUTHEAST ALASKA), SUPPORTING A SLIGHT RISK OF HIGH
WINDS FOR THE ALEUTIANS AND SOUTHERN ALASKA. THE PETS (ESPECIALLY THE ECENS)
INDICATE AT LEAST A 20% CHANCE OF WIND SPEEDS EXCEEDING THE 85TH PERCENTILE AND
40 MPH. THE VERY COLD WEATHER AND HIGH WINDS ALONG THE SOUTHERN TIER OF THE
STATE INCREASES THE THREAT FOR HEAVY FREEZING SPRAY AT TIMES IN MARINE AREAS IN
ADDITION TO HAZARDOUS LOW WIND CHILLS POSSIBLE, IMPACTING VULNERABLE
POPULATIONS.
OVER THE CENTRAL PACIFIC, MID-LEVEL TROUGHING IS FAVORED UNDERNEATH THE STRONG
RIDGE CENTER OVER THE NORTH-CENTRAL PACIFIC, WHICH MAY LEAD TO KONA LOW
DEVELOPMENT TO THE WEST OF THE HAWAIIAN ISLANDS EARLY IN WEEK-2. PETS INDICATE
ELEVATED (>60%) CHANCES FOR 3-DAY AMOUNTS EXCEEDING THE 85TH PERCENTILE WITH
ELEVATED CHANCES OF TOTALS EXCEEDING TWO INCHES. AS THESE SIGNALS ARE FAVORED
TO SHIFT EASTWARD WITH TIME, LOCALLY HEAVY PRECIPITATION AND OTHER ADVERSE
IMPACTS LOOKS TO OVERSPREAD MORE OF THE HAWAII ISLANDS (MAINLY FROM MAUI
WESTWARD) THROUGHOUT WEEK-2.
FORECASTER: NICK NOVELLA
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