779 FXUS21 KWNC 142043 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EST December 14 2025 SYNOPSIS: A persistent pattern featuring strong mid-level and surface low pressure over the North Pacific will favor a variety of weather hazards, including high winds, heavy precipitation, and high-elevation snow across the western Contiguous U.S. (CONUS) throughout week-2. The best chances for impactful weather extends across northwestern and northern California, the Sierra Nevada, and adjacent southwestern Oregon, where high risks for heavy precipitation and heavy mountain snowfall are posted. Surface low pressure over the Great Plains along with surface high pressure over the Southeast U.S. are expected to induce potentially hazardous winds over much of the Plains, Mississippi Valley, and western Great Lakes. Farther north, strong surface high pressure over the Yukon and interior Alaska is favored to entrench extremely cold air into southeastern Alaska for all of week-2. HAZARDS High risk of heavy precipitation for the Sierra Nevada, northern and northwestern California, and adjacent southwestern Oregon, Mon-Thu, Dec 22-25. High risk of heavy snow for the Sierra Nevada and California Cascades, Mon-Thu, Dec 22-25. Moderate risk of heavy precipitation for the Sierra Nevada, northern California, the central California Coast, and southwestern Oregon, Mon-Fri, Dec 22-26. Moderate risk of heavy precipitation for southwestern California including the Coastal Ranges, Tue-Thu, Dec 23-25. Moderate risk of heavy snow for the southern Cascades, Klamath Range, and Sierra Nevada, Mon-Fri, Dec 22-26. Moderate risk of heavy snow for much of the Bitterroot and Absaroka Ranges, Mon-Fri, Dec 22-26. Slight risk of heavy snow for the Cascades, Klamath, and Sierra Nevada, Mon-Sun, Dec 22-28. Slight risk of heavy snow for the central and northern Rockies, Mon-Sun, Dec 22-28. Slight risk of heavy precipitation along and near the entire West Coast, Mon-Sun, Dec 22-28. Moderate risk of high winds for much of the central and northern West Coast States, Great Basin, Intermountain West, and central and northern Rockies, Mon-Sun, Dec 22-28. Slight risk of high winds for much of the central and western Contiguous United States (CONUS), Mon-Sun, Dec 22-28. Moderate risk of much below-normal temperatures for southeastern Alaska, Mon-Sun, Dec 22-28. Slight risk of much below-normal temperatures for much of south-central and southeastern Alaska, Mon-Sun, Dec 22-28. Slight risk of high winds for much of southern Alaska, including the Alaska Range, Mon-Sun, Dec 22-28. Flooding possible along much of the West Coast. DETAILED SUMMARY FOR WEDNESDAY DECEMBER 17 - SUNDAY DECEMBER 21: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR MONDAY DECEMBER 22 - SUNDAY DECEMBER 28: Today's model solutions continue to be in excellent agreement forecasting an amplified quasi-stationary pattern featuring a strong mid-level ridge over the north-central Pacific and the Bering Strait, below-normal downstream 500-hPa heights stretching from a strong polar vortex feature near Hudson Bay through southwestern Canada and into the eastern North Pacific, a broad ridge across much of the CONUS, and mid-level troughing from eastern Canada into the North Atlantic. The strength of these features will wax and wane slightly over time, and their exact positions will drift slightly, but the overall pattern remains remarkably stable throughout week-2, as shown by almost all guidance. PETs continue to highlight enhanced chances for hazardous below normal temperatures across portions of south-central and southeastern Alaska. The Bering Sea mid-level ridge and the downstream mid-level trough should maintain stable, cold high pressure across interior Alaska and the Yukon throughout week-2. Deterministic models show temperatures below -30 deg. F periodically across the southeastern Alaska mainland, and below -15 deg. F as far south as the eastern tier of the Panhandle. The largest departures from normal are expected in Southeast Alaska, where deterministic models forecast temperatures 20 to 30 deg. F below normal at times. The GEFS PET indicates a greater than 20 percent chance for temperatures to drop among the coldest 2 percent of the historic observations. This justifies a moderate risk of much below normal temperatures in southeastern Alaska. The mid-level ridge in the Bering Sea weakens slightly with time, but with the downstream trough remaining potent, cold surface high pressure should expand westward with time. This will entrench frigid conditions in southeastern parts of the state, and bring much colder air farther west, eventually covering most of the state. Today's guidance does not hint at any weakening of the cold high pressure system later week-2, and the beginning of week-2 may be slightly milder than conditions at the end of week-2. 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. The 0z ensembles from the European (ECENS), Canadian (CNENS), and GEFS depict an amplified mid-level ridge centered over the Bering Sea, with an amplified downstream mid-level trough extending from the North Pacific well west off the California Coast into the high latitudes of Canada. This set-up should keep surface high pressure across much of Alaska and the Yukon throughout week-2. At the same time, mean low pressure is favored in the Gulf of Alaska, centered near the south-central or southeastern Alaska coast. The pressure gradient between these features increases the likelihood for episodes of high winds across much of southern Alaska from the central Aleutian Islands through Southeast Alaska, including some interior mountains. High winds would be particularly favored in gaps and inlets, and close to the lowest surface pressures, but the precise locations of the highest winds will vary from day to day. Probabilistic Extremes Tools (PETs) show enhanced chances of wind speeds exceeding the 85th climatological percentile. Therefore, a slight risk of high winds is posted for most of southern and southeastern Alaska for all of week-2. Most model guidance maintains an amplified mid-level trough with an axis stretching from southwestern Canada into the North Pacific upstream from a broad anomalous ridge covering most of the CONUS. This will likely result in an enhanced jet stream across much of the western CONUS that will essentially persist through week-2. As a result, stormy conditions featuring heavy precipitation (including heavy mountain snowfall) and high winds will be common across the western CONUS through the period. The location of atmospheric rivers will determine where the most impactful conditions occur, and at this time it looks like the focus will be over the central and southern Far West through the middle of the period before shifting northward toward the Pacific Northwest. Today's PETs are even more robust than yesterday in forecasting high chances of heavy precipitation and heavy high-elevation snowfall across California for much of week-2. The ECENS PET shows chances exceeding 60 percent that precipitation totals will be among the wettest 15 percent of the historic envelope during one 3-day period, with the GEFS and ECENS PET indicating similar odds for raw amounts exceeding 3 inches in parts of the Sierra Nevada, California Cascades, and the central West Coast during this period. Therefore, a high risk of heavy precipitation and heavy high-elevation snows is posted across this region into the middle of week-2. The GEFS snow water equivalent (SWE) PET indicates a better than 20 percent chance that more than 2 inches of precipitation will fall as snow in the higher elevations, with deterministic models dropping the largest amounts on the central Sierra Nevada. To the north and south of this area, moderate risks of heavy precipitation and heavy high-elevation snows are posted through the middle of week-2. For a few days near the middle of the period, most tools agree that heavy precipitation will extend southward into southern California, and a moderate risk of heavy precipitation is posted there for Dec 23-25. Late in the week, most guidance shows the heaviest precipitation shifting northward into the Pacific Northwest, but there is not enough agreement on the specifics of location and intensity to justify a moderate risk of any precipitation hazard there. But with the mid-level set-up remaining favorable for inclement weather through the period, slight risks of heavy precipitation and heavy high-elevation snowfall are maintained across a large portion of the Far West for the entirety of week-2. These factors also indicate a risk of flooding along and near most of the West Coast, especially in areas where antecedent conditions were unusually wet. Continued precipitation accumulations on saturated soils also brings the additional risk of landslides and debris flows in steep terrain or burn scars. The incoming moisture associated with this enhanced jet is likely to push well inland, resulting in potentially heavy snow for parts of the central and northern Rockies. Models have backed off somewhat on their snowfall forecasts compared to yesterday, but the GEFS SWE PET and raw deterministic snowfall output support a moderate risk of heavy snow over the Bitterroot Ranges, extending southeastward into northwestern Wyoming. In several areas, liquid-equivalent totals could exceed an inch within 3 days. Over a much broader portion of the central and northern Rockies, the persistent mid-level pattern is expected to maintain a set-up favorable for heavy high-elevation snowfall across the higher elevations of the Interior West, and a slight risk of heavy snow is posted for all of week-2 over most of the central and northern Rockies. Along with heavy precipitation and snow, high winds reaching hazardous criteria are also possible associated with this atmospheric river (AR) event. This is well indicated by the ECENS PET, which shows at least a 20% chance of 3-day maximum wind speeds exceeding the 85th percentile for much of the CONUS at times throughout the week. In the GEFS and ECENS PETs, the most elevated odds for high winds are from the Rockies westward, The ECENS shows a greater than 30 percent chance for winds above the 85th percentile there, with chances reaching as high as 60 to 80 percent in southern Utah, northern California and parts of the northern Intermountain West and Pacific Northwest. The CNENS is also fairly robust in depicting odds for high winds in the West, with the GEFS PET being more muted but still indicating somewhat enhanced chances for high winds. These indicators are consistent with the persistent stormy pattern forecast for much of the West during week-2. Farther east, individual shortwaves will periodically be ejected eastward from the North Pacific trough, inducing one or more episodes of cyclogenesis over the Plains. Farther east, surface high pressure should be fairly persistent downstream from the axis of the mid-level ridge covering the CONUS. Between these systems, a tight pressure gradient may periodically be established across the central CONUS, somewhat increasing the odds for episodes of high winds across the central CONUS. With the pattern changing little over the course of week-2, a slight risk of high winds is supported for the entire period. FORECASTER: Rich Tinker $$