736 FXUS21 KWNC 211911 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EST December 21 2025 SYNOPSIS: 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. Heading into the New Year, mid-level low pressure may shift closer to the West Coast or even inland, which would lower snow elevation levels across the Pacific Northwest. An elevated chance of heavy snow and high winds are forecast to continue for much of the West into the beginning of January 2026. 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 and northwestern Oregon, Mon, Dec 29. High risk of heavy snow for the northern Cascades, Mon, Dec 29. Moderate risk of heavy precipitation for the Pacific Northwest, Mon-Tue, Dec 29-30. Moderate risk of heavy snow for the Cascades and Klamath mountains, Mon-Sun, Dec 29-Jan 4. Slight risk of heavy precipitation for the Pacific Northwest and northern California, Mon-Sun, Dec 29-Jan 4. Slight risk of heavy snow for the Cascades, Klamath, and Sierra Nevada Mountains, Mon-Sun, Dec 29-Jan 4. Moderate risk of heavy snow for the Northern Rockies and part of the Northern Intermountain West, Mon-Sun, Dec 29-Jan 4. Slight risk of heavy snow for the higher elevations of the interior West, Mon-Sun, Dec 29-Jan 4. Moderate risk of high winds for parts of the West, Mon-Sun, Dec 29-Jan 4. Slight risk of high winds for much of the West, Great Plains, and Upper Mississippi Valley, Mon-Sun, Dec 29-Jan 4. Moderate risk of much below-normal temperatures for much of southern Mainland and Southeast Alaska, Mon and Thu-Sun, Dec 29 and Jan 1-4. Slight risk of much below-normal temperatures for southern and central Mainland and Southeast Alaska, Mon-Sun, Dec 29-Jan 4. Slight risk of high winds for much of southern Alaska, including the Alaska Range, Mon-Sun, Dec 29-Jan 4. Flooding possible for parts of northern California and the Pacific Northwest. DETAILED SUMMARY FOR WEDNESDAY DECEMBER 24 - SUNDAY DECEMBER 28: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR MONDAY DECEMBER 29 - SUNDAY JANUARY 04: The ECENS, GEFS, and CMCE depict a 500-hPa trough amplifying southward from the Gulf of Alaska to the Pacific Northwest early in week-2. This anomalous 500-hPa trough favors a continuation of the wet pattern over the West and also the return of an atmospheric river (AR) to the Pacific Northwest prior to or by December 29. The GEFS and ECENS have near a 60 percent chance that integrated vapor transport values (IVT) values exceed 250 kg/m/s across western Washington and northwestern Oregon which is a good signal for an AR. The ECENS indicates that this AR does not shift south to California and implies at least a brief end to AR events along the West Coast, beginning on December 31. This would be consistent with the multi-model ensemble mean solutions trending towards the 500-hPa trough axis shifting to the West Coast or perhaps even inland. If this were to occur, then chances for heavy precipitation may decrease later in week-2 but lower 500-hPa heights would increase the chance of lower elevation snowfall outside of the Cascades. Based on the evolving 500-hPa longwave pattern, IVT model guidance, and 1 to 3-day precipitation amounts from the ECENS and GEFS, a high risk (> 60% chance) of heavy precipitation is designated for western Washington and northwestern Oregon on December 29 with the moderate risk (40-60% chance) discontinued after the 30th. The highest risk of heavy snow remains across the northern Cascades, valid on December 29. Although chances for heavy precipitation are expected to decrease later in week-2, the amplified 500-hPa trough along with the GEFS Probabilistic Extremes Tool (PET) having near a 40 percent chance of snow water equivalent (SWE) amounts exceeding 1 inch per 3-day period supports a moderate risk of heavy snow for the Cascades and parts of the Klamath Mountains throughout week-2. Based on the GEFS and ECMWF PETs, slight risks of heavy precipitation and high elevation snow are also posted for the Pacific Northwest and parts of California, valid from December 29 to January 4. Given the ongoing river flooding and saturated soils along with an increased chance of above-normal precipitation during week-2, a possible flooding hazard remains posted for portions of the Pacific Northwest and northern California. The amplified 500-hPa trough upstream and model guidance favor a slight to moderate risk of heavy snow throughout week-2 from the northern Rockies south to the higher elevations of Utah and Colorado. Since the models have trended towards the amplified 500-hPa trough shifting eastward with associated height falls, the slight risk of heavy snow was expanded to include parts of Utah. The large spatial extent of hazardous snow is supported by the GEFS SWE PET and also consistent with the week-2 outlook having a 40-50% chance of above-normal precipitation. A moderate risk of heavy snow remains focused on the northern Rockies where the heaviest snowfall is predicted. The longwave pattern and enhanced Pacific flow support periods of high winds across much of the West 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 over the Great Plains. Therefore, a slight risk of high winds is posted for much of the Great Plains and Upper Mississippi Valley. Although above-normal precipitation is favored for southern California and the Southwest during week-2, low forecast confidence on the timing of any heavy precipitation precludes any hazard for southern California, Arizona, or New Mexico. In addition, snow levels are likely to be on the higher side until the eastern Pacific trough shifts well inland and 500-hPa heights fall. Models are trending towards this outcome later in week-2 and the introduction of a heavy snow hazard may be necessary for the higher elevations of Arizona and New Mexico in subsequent outlooks. Arctic high pressure is likely to persist over Alaska into the New Year. Based on consensus of the GEFS and ECMWF PETs indicating more than 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 eastern Aleutians on December 29. A brief easing of the anomalous cold is expected before bitterly cold temperatures return by New Year's Day. Therefore, the moderate risk for much below normal temperatures is also valid from January 1 to 4. The slight risk goes through the entirety of week-2 and includes all of Alaska south of the Brooks Range. Gusty northerly winds may accompany the 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 $$