938
FXUS21 KWNC 271938
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST DECEMBER 27 2025
SYNOPSIS: AT THE OUTSET OF WEEK-2, MID-LEVEL LOW PRESSURE REMAINS FORECAST
ACROSS WESTERN NORTH AMERICA FAVORING CONTINUED ENHANCED ONSHORE FLOW AND
INCREASED CHANCES OF HEAVY PRECIPITATION (COASTAL RAIN AND HIGH ELEVATION SNOW)
FOR THE WEST COAST OF THE CONTIGUOUS U.S. (CONUS). UNCERTAINTY INCREASES LATER
IN THE PERIOD AS DYNAMICAL MODELS INDICATE A TREND TOWARD INCREASED MID-LEVEL
LOW (HIGH) PRESSURE ACROSS THE CENTRAL PACIFIC (WESTERN CONUS). THIS COULD
RESULT IN A DRYING TREND ACROSS THE WEST COAST TOWARD THE END OF WEEK-2 AS WELL
AS MODERATING TEMPERATURES ACROSS ALASKA. WHILE THE PATTERN ACROSS THE EASTERN
U.S. IS FORECAST TO BE MORE VARIABLE, INCREASING HIGH LATITUDE BLOCKING
COMBINED WITH INCOMING SHORTWAVE ENERGY DIGGING UNDERNEATH COULD FAVOR A MORE
ACTIVE WEATHER PATTERN.
HAZARDS
MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR SOUTHWESTERN MAINLAND
ALASKA, THE ALASKA PENINSULA, AND EASTERN ALEUTIANS, SUN-MON, JAN 4-5.
SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR ALL OF ALASKA WITH THE
EXCEPTION OF THE NORTH SLOPE AND SOUTHEAST ALASKA, SUN-WED, JAN 4-7.
SLIGHT RISK OF HIGH WINDS FOR THE ALASKA PENINSULA, SOUTHERN MAINLAND ALASKA,
AND SOUTHEASTERN ALASKA, SUN-WED, JAN 4-7.
SLIGHT RISK OF HEAVY PRECIPITATION ACROSS THE WEST COAST OF THE CONUS, SUN-THU,
JAN 4-8.
SLIGHT RISK OF HEAVY PRECIPITATION ACROSS PORTIONS OF THE LOWER MISSISSIPPI
VALLEY, TENNESSEE VALLEY, AND SOUTHEAST, TUE-SAT, JAN 6-10.
SLIGHT RISK OF HEAVY SNOW ACROSS PORTIONS OF THE CASCADES, KLAMATH, AND SIERRA
NEVADA MOUNTAINS, SUN-THU, JAN 4-8.
SLIGHT RISK OF HEAVY SNOW ACROSS PORTIONS OF THE UPPER MISSISSIPPI VALLEY,
GREAT LAKES, AND THE NORTHEAST, SUN-TUE, JAN 4-6.
SLIGHT RISK OF HIGH WINDS ACROSS MUCH OF THE CONUS WEST OF THE ROCKIES,
SUN-THU, JAN 4-8.
DETAILED SUMMARY
FOR TUESDAY DECEMBER 30 - SATURDAY JANUARY 03:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SUNDAY JANUARY 04 - SATURDAY JANUARY 10: DURING WEEK-2, THE 0Z ECMWF AND
CANADIAN ENSEMBLES DEPICT A QUICK MID-LEVEL PATTERN TRANSITION ACROSS THE
PACIFIC WITH A WEAKENING OF THE RIDGE TO THE SOUTH OF THE ALEUTIANS, TROUGHING
EMERGING ACROSS THE CENTRAL PACIFIC, AND HINTS OF RIDGING NEAR THE WEST COAST
OF THE CONUS BY THE END OF WEEK-2. THIS WOULD BE CONSISTENT WITH A WEAKENING
NEGATIVE PHASE OF THE PACIFIC NORTH AMERICAN (-PNA) PATTERN. THE GEFS IS SLOWER
AND WEAKER WITH THE PATTERN EVOLUTION, ADDING TO SOME UNCERTAINTY WITH THE
EVENTUAL OUTCOME WHICH COULD ULTIMATELY HAVE IMPLICATIONS DOWNSTREAM OVER THE
CONUS LATER IN WEEK-2.
FOLLOWING A PERIOD OF RELATIVELY DRIER WEATHER IN WEEK-1 ACROSS THE WEST COAST
TIED TO A TRANSIENT MID-LEVEL RIDGE, ANOTHER TROUGH IS PREDICTED TO BUILD OVER
WESTERN NORTH AMERICA BY THE OUTSET OF WEEK-2 FAVORING A RETURN TO ENHANCED
PRECIPITATION CHANCES OVER THE REGION. BOTH THE GEFS AND ECMWF PROBABILISTIC
EXTREMES TOOLS (PETS) DEPICT AT LEAST A 20 PERCENT CHANCE 3-DAY PRECIPITATION
TOTALS EXCEED THE 85TH CLIMATOLOGICAL PERCENTILE AND 1-INCH ACROSS THE ENTIRE
WEST COAST THROUGH THE MIDDLE OF THE PERIOD. PROBABILITIES FOR REACHING THE
85TH PERCENTILE ARE HIGHER (ABOVE 40 PERCENT) IN THE ECMWF PET ACROSS THE
SOUTHWEST COMPARED TO THE GEFS PET, WITH UNCALIBRATED TOOLS FAVORING HIGHER
PRECIPITATION TOTALS OVER THE PACIFIC NORTHWEST. A BROAD SLIGHT RISK FOR HEAVY
PRECIPITATION IS POSTED ACROSS THE ENTIRE WEST COAST, VALID JAN 4-8, WITH A
CORRESPONDING SLIGHT RISK OF HEAVY SNOW ACROSS HIGHER ELEVATIONS OF THE
CASCADES, KLAMATH, AND SIERRA NEVADA MOUNTAINS SUPPORTED BY THE GEFS SNOW WATER
EQUIVALENT (SWE) PET. HEAVY SNOW IS ALSO POSSIBLE FURTHER INLAND ACROSS THE
GREAT BASIN AND ROCKIES, ALTHOUGH PROBABILITIES FOR DAILY SNOWFALL GREATER THAN
4 INCHES IN THE ECMWF AND GEFS ENSEMBLES ARE LOWER COMPARED TO CLOSER TO THE
COAST PRECLUDING INCLUSION IN THE HAZARD. THERE ARE SOME INDICATIONS OF A
STRONGER SURGE OF MOISTURE INTO THE NORTHWEST TOWARD THE MIDDLE OF THE PERIOD,
WITH INCREASED 24-HOUR PRECIPITATION TOTALS IN THE UNCALIBRATED GUIDANCE.
STRONGER WINDS MAY ALSO BE POSSIBLE ACROSS THE PACIFIC NORTHWEST, WITH THE
ECMWF PET DEPICTING HIGH PROBABILITIES (GREATER THAN 60 PERCENT) FOR WIND
SPEEDS EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE ASSOCIATED WITH A
TIGHTENING SURFACE PRESSURE GRADIENT. TRENDS WILL CONTINUE TO BE MONITORED FOR
A POTENTIAL UPGRADE TO A MODERATE RISK TOMORROW.
FURTHER DOWNSTREAM ACROSS THE CONUS, SHORTWAVE DISTURBANCES ARE LIKELY TO
PROPAGATE THROUGH THE MEAN FLOW. THE FIRST IS FAVORED EARLY IN THE PERIOD, WITH
ANOTHER SYSTEM POSSIBLE LATER ON IN WEEK-2. THE ECMWF ENSEMBLE ALONG WITH
RECENT DETERMINISTIC RUNS DEPICT A MORE AMPLIFIED SYSTEM AND ASSOCIATED SURFACE
LOW PRESSURE ACROSS THE NORTHEASTERN U.S. EARLY IN WEEK-2 WHICH COULD BRING
INCREASED CHANCES FOR HEAVY SNOW INITIALLY ACROSS THE UPPER MISSISSIPPI VALLEY
AND GREAT LAKES, AND THEN INTO PORTIONS OF THE NORTHEAST. THE GEFS IS FLATTER
WITH THIS INITIAL WAVE, ALTHOUGH ITS CORRESPONDING DETERMINISTIC SOLUTIONS ALSO
DEPICT AREAS OF SNOW OR WINTRY WEATHER ACROSS THESE SAME AREAS. THEREFORE, A
SLIGHT RISK FOR HEAVY SNOW IS HIGHLIGHTED ACROSS PORTIONS OF THE UPPER
MISSISSIPPI VALLEY, GREAT LAKES, AND THE NORTHEAST, JAN 4-6. A SECOND SHORTWAVE
LATER IN WEEK-2 MAY HAVE MORE OF A SOUTHERN STREAM COMPONENT WITH BOTH THE
ECMWF AND GEFS PETS DEPICTING AT LEAST A 20 PERCENT CHANCE 3-DAY PRECIPITATION
TOTALS EXCEED THE 85TH CLIMATOLOGICAL PERCENTILE AND 1-INCH OVER PARTS OF THE
LOWER MISSISSIPPI VALLEY, TENNESSEE VALLEY, AND SOUTHEAST DURING THE SECOND
HALF OF THE PERIOD. THIS SUPPORTS A SLIGHT RISK FOR HEAVY PRECIPITATION OVER
THESE AREAS, JAN 6-10. THE NORTHWARD TRAJECTORY OF THIS MOISTURE IS UNCERTAIN,
ALTHOUGH A SUBSTANTIAL HIGH-LATITUDE BLOCKING RIDGE PREDICTED OVER NORTHEASTERN
NORTH AMERICA COULD SUPPORT GREATER AMPLIFICATION OF NEGATIVE 500-HPA HEIGHT
ANOMALIES UNDERNEATH THIS FEATURE AT THE END OF WEEK-2.
SURFACE HIGH PRESSURE IS FORECAST TO PERSIST ACROSS MUCH OF ALASKA AND THE
YUKON THROUGHOUT WEEK-2. CONVERSELY, MEAN LOW PRESSURE IS FAVORED IN THE GULF
OF ALASKA. THE PRESSURE GRADIENT BETWEEN THESE FEATURES RESULTS IN ELEVATED
CHANCES FOR EPISODES OF HIGH WINDS ACROSS MUCH OF SOUTHERN ALASKA FROM THE
CENTRAL ALEUTIAN ISLANDS THROUGH SOUTHEAST ALASKA. HIGH WINDS WOULD BE
PARTICULARLY FAVORED IN GAPS AND INLETS. THE PETS DEPICT AT LEAST A 20 PERCENT
CHANCE WIND SPEEDS EXCEED THE 85TH CLIMATOLOGICAL PERCENTILE AND 40-MPH OVER
SOME OF THESE AREAS THROUGH THE MIDDLE OF THE PERIOD. THERE IS STILL SOME
SIGNAL FOR HIGH WINDS AT THE END OF WEEK-2, BUT GIVEN INCREASING MODEL SPREAD
AND A TRANSITIONING PATTERN THERE IS INSUFFICIENT CONFIDENCE TO ISSUE A
FULL-WEEK HAZARD. THEREFORE A SLIGHT RISK OF HIGH WINDS IS POSTED FOR MOST OF
SOUTHERN AND SOUTHEASTERN ALASKA FOR JAN 4-7.
PETS CONTINUE TO HIGHLIGHT ENHANCED CHANCES FOR TEMPERATURES TO FALL TO NEAR
HAZARDOUS THRESHOLDS ACROSS MUCH OF SOUTHERN, INTERIOR, AND SOUTHEAST ALASKA,
DRIVEN IN PART BY THE PRESSURE GRADIENT DISCUSSED ABOVE. A MODERATE RISK OF
MUCH BELOW-NORMAL TEMPERATURES IS POSTED FOR SOUTHERN ALASKA WEST OF PRINCE
WILLIAMS SOUND, THE LOWER YUKON, AND THE ALASKAN PENINSULA, VALID JAN 4-5,
WHILE A BROADER SLIGHT RISK IS POSTED FOR ALL OF THE ALASKAN MAINLAND WITH THE
EXCEPTION OF THE NORTH SLOPE AND SOUTHEAST ALASKA FOR JAN 4-7. THE COMBINATION
OF 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. AS THE RIDGE OVER THE CENTRAL PACIFIC BEGINS TO BREAK DOWN, MODERATION
OF TEMPERATURES IS LIKELY TOWARD THE SECOND HALF OF WEEK-2, PARTICULARLY ACROSS
INTERIOR AND EASTERN PARTS OF MAINLAND ALASKA.
FORECASTER: THOMAS COLLOW
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