513 FXUS21 KWNC 222122 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EST December 22 2025 SYNOPSIS: Mid-level low pressure over the northeastern Pacific is expected to expand southward throughout week-2, bringing increased risk of heavy precipitation and heavy snow initially to the Pacific Northwest, expanding southward to parts of California by the middle of the period. 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. The pattern may lead to high winds across southern Alaska, leading to dangerously low wind chills. As a possibly strong surface low from the end of week-1 departs the Northeast at the beginning of week-2, there is enhanced risk of high winds for the northeastern CONUS. HAZARDS Moderate risk of heavy precipitation for the Pacific Northwest, Mon, Dec 30. Moderate risk of heavy snow for the Cascades, Tue-Mon, Dec 30-Jan 5. Moderate risk of heavy snow for the Klamath Mountains and Sierra Nevada, Thu-Sat, Jan 1-3. Slight risk of heavy precipitation for the Pacific Northwest and central and northern California, Tue-Mon, Dec 30-Jan 5. Slight risk of heavy snow for the Cascades, Klamath, and Sierra Nevada Mountains, Tue-Mon, Dec 30-Jan 5. Moderate risk of heavy snow for the Northern Rockies and part of the Northern Intermountain West, Tue-Mon, Dec 30-Jan 5. Slight risk of heavy snow for the higher elevations of the interior West, Tue-Mon, Dec 30-Jan 5. Moderate risk of high winds for parts of the West, Tue-Mon, Dec 30-Jan 5. Slight risk of high winds for much of the West, Great Plains, and Upper Mississippi Valley, Tue-Mon, Dec 30-Jan 5. Slight risk of high winds for the Northeast and northern portions of the Mid-Atlantic, Tue-Wed, Dec 30-Dec 31. Moderate risk of much below-normal temperatures for parts of central and southern Mainland Alaska and Southeast Alaska, Tue, Dec 30 and Fri-Mon, Jan 2-5. Slight risk of much below-normal temperatures for southern and central Mainland and Southeast Alaska, Tue-Mon, Dec 30-Jan 5. Slight risk of high winds for much of southern Alaska, including the Alaska Range, Tue-Mon, Dec 30-Jan 5. Flooding possible for parts of northern California and the Pacific Northwest. DETAILED SUMMARY FOR THURSDAY DECEMBER 25 - MONDAY DECEMBER 29: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR TUESDAY DECEMBER 30 - MONDAY JANUARY 05: The ECENS, GEFS, and CMCE continue to be in good agreement and 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. Early in week-2, the ECENS depicts large increased probabilities for enhanced integrated vapor transport (IVT) values initially impacting the Pacific Northwest and shifting southward through week-2. Areas of high risk for heavy precipitation and/or heavy snow time off before the period. Areas of moderate risk for heavy precipitation for the Pacific Northwest, Dec 30, and heavy snow for the Cascades throughout week-2, continue to be designated based on uncalibrated model guidance. A moderate risk is highlighted for the Klamath Mountains and Sierra Nevada the middle of week-2, as the enhanced moist flow shifts southward given increased signal in the IVT and uncalibrated tools. The slight risk area is expanded to include portions of central California in addition to northern California and the Pacific Northwest throughout the period given increases in IVT signal further south compared to yesterday. 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. 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. 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 across the West. 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. As a potentially strong surface low exits the Northeast at the beginning of week-2, enhanced winds could linger from the end of week-1 for the northeastern CONUS. A slight risk of high winds are designated for portions of the Northeast and northern portions of the Mid-Atlantic Dec 30-31. The ECENS PET shows at least a 20% chance of wind speeds exceeding the 85th percentile climatologically and 20 mph, further supported by recent deterministic models and uncalibrated ensemble guidance. Arctic high pressure is likely to persist over Alaska into the New Year. The risk of much below normal temperatures expected initially to be most likely across eastern Alaska, expanding westward during week-2. A brief easing of the anomalous cold is expected December 31 to January 1, before building back again by January 2. 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. Additionally, this pattern may be conducive to heavy precipitation lingering from the end of week-1 into the onset of week-2, resulting in a slight risk of heavy snow for northern portions of Southeast Alaska (the Panhandle) and heavy precipitation (more likely rainfall) across southern portions, December 30. A storm system is predicted to form in the Central Pacific by the start of week-2, which could approach Hawaii. This would increase chances for above-normal precipitation initially for the western islands shifting eastward with time. Some areas may have increased likelihood of heavy precipitation during week-2. FORECASTER: Melissa Ou $$