363 FXUS21 KWNC 122001 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EST December 12 2025 SYNOPSIS: Strong mid-level and surface low pressure over the North Pacific bring the potential for a variety of hazardous weather including high winds, heavy precipitation, and high-elevation snow across the western Contiguous U.S. (CONUS) throughout the week-2 period. Surface low pressure over the Great Plains along with surface high pressure over the Southeast U.S. pair to produce potentially hazardous winds over much of the Plains, Upper Mississippi Valley, and Great Lakes. Strong surface high pressure over the Yukon is favored to push extremely cold air into southeastern Alaska, potentially below hazardous criteria. HAZARDS Moderate risk of heavy snow for the Cascades, Klamath, and northern and central Sierra Nevadas, Sat-Fri, Dec 20-26. Moderate risk of heavy snow for the Northern Rockies, Sat-Fri, Dec 20-26. Moderate risk of heavy snow for the Central and Southern Rockies, and the Wasatch Range, Mon-Fri, Dec 22-26. Slight risk of heavy snow for the Cascades, Klamath, and Sierra Nevadas, Sat-Fri, Dec 20-26. Slight risk of heavy snow for the Rockies and the ranges of the Intermountain West, Sat-Fri, Dec 20-26. Moderate risk of heavy precipitation of portions of northern California and coastal portions of Oregon and Washington, Sat-Fri, Dec 20-26. Moderate risk of heavy precipitation for coastal portions of central and southern California, Mon-Fri, Dec 22-26. Slight risk of heavy precipitation along the entire West Coast, Sat-Fri, Dec 20-26. Moderate risk of high winds for much of northern California, the Pacific Northwest, northern Great Basin, and Northern Rockies, Sat-Fri, Dec 20-26. Slight risk of high winds for much of California, Pacific Northwest, Great Basin, Northern Rockies, Northern and Central Plains, Middle and Upper Mississippi Valley, and Great Lakes, Sat-Fri, Dec 20-26. Slight risk of high winds for the Alaska Peninsula, southern Mainland Alaska, and southeastern Alaska, Sat-Fri, Dec 20-26. Moderate risk of much below-normal temperatures for southeastern Alaska, Sat-Wed, Dec 20-24. Slight risk of much below-normal temperatures for much of south-central and southeastern Alaska, Sat-Fri, Dec 20-26. Flooding possible for portions of the Pacific Northwest and northern California. DETAILED SUMMARY FOR MONDAY DECEMBER 15 - FRIDAY DECEMBER 19: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR SATURDAY DECEMBER 20 - FRIDAY DECEMBER 26: Todays model solutions continue to depict with excellent agreement an active an d persistent synoptic pattern over the North Pacific and western North America. The 0z ECMWF, GEFS, and Canadian ensembles depict an amplified mid-level ridge c entered over the Bering Sea, with an amplified downstream mid-level trough exten ding from the North Pacific across the Pacific Northwest and into the high latit udes of Canada. At the surface, this set-up favors persistent high pressure acro ss 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 brings increased chances for episodes of high winds across much of southern Alas ka from the central Aleutian Islands through Southeast Alaska. High winds would be particularly favored in gaps and inlets. Probabilistic Extremes Tools (PETs) show enhanced chances of wind speeds exceeding the 85th climatological percentil e. Therefore, a slight risk of high winds is posted for most of southern and sou theastern Alaska for all of week-2. PETs continue to highlight enhanced chanc es for temperatures to fall to near hazardous thresholds across portions of sout h-central, Interior, and Southeast Alaska. As the Bering Sea ridge slowly weaken s, the anomalous cold (and associated northerly flow) will gradually expand west ward across the state. A moderate risk is posted for Southeast Alaska for Dec 20 -24, while a broader slight risk is maintained for much of south-central and sou theast Alaska for all of week-2. Temperatures between -20 deg F and -35 deg F ar e predicted to be widespread across much of inland Alaska, with -40 deg F temper atures indicated by the PETs over the eastern Interior to the north of Fairbanks . Closer to the coast, temperatures are expected to range between 0 and -15 deg F (Anchorage near -10 deg F), while the southern half of Southeast Alaska is pre dicted to be somewhat milder, with high temperatures about +10 deg F. The combin ation of very cold weather and high winds along the southern tier of the state i ncreases the threat for heavy freezing spray at times near larger bodies of wate r. The 0z ECENS, 0z GEFS, and 0z CMCE model solutions depict persistent mid-l evel troughing over the North Pacific and broad positive 500-hPa height anomalie s across much of the southern CONUS, resulting in an enhanced jet stream over th e Pacific Northwest. The Integrated Vapor Transport (IVT) tool also indicates de ep low-level moisture streaming into the West Coast throughout the forecast peri od, with both the ECMWF and GEFS showing probabilities exceeding 40% for IVT to exceed 250 kg/m/s. The PETs and uncalibrated precipitation guidance supports a s light risk of heavy precipitation along the entire West Coast for all of week-2. A moderate risk for heavy precipitation is indicated for the Pacific Northwest, Northern and portions of Central California, also for all of week-2. Precipitat ion amounts of 2 inches are predicted by PET guidance within this broad region o f elevated onshore flow from Washington state southward to Central California. B oth the GEFS and ECMWF indicate AR activity to shift further south by the middle of week-2, and the potential for heavy precipitation with it, therefore a moder ate risk of heavy precipitation is posted for coastal portions of central and so uthern California for Dec 22-26. This forecasted heavy precipitation, in additio n to the antecedent week-1 precipitation, is likely to aggravate flooding issues for the Pacific Northwest, with a flooding possible hazard remaining posted and extended into northwestern California. Continued precipitation accumulations on saturated soils brings the additional risks of landslides and debris flows in s teep terrain or burn scars, as well as the potential for urban and flash floodin g across the region. The incoming moisture associated with this atmospheric r iver is likely to push well inland, resulting in potentially heavy snow for many mountain ranges across the West. Uncalibrated probabilities from both the ECENS and GEFS for daily accumulations of over 6 inches exceed 40% in some locations throughout the week, and the GEFS PET for snow water equivalent (SWE) indicates at least a 20% chance of 3-day SWE to exceed the 85th climatological percentile and at least 1 inch for much of the Cascades, Sierras, and Northern and Central Rockies throughout the week. Based on the GEFS PET and uncalibrated daily snowfa ll totals, a moderate risk of heavy snow for all of week-2 for the Cascades, Kla math, and northern and central Sierras, and a slight risk of heavy snow extendin g over the southern Sierras, also for the whole week. Further east, a broad area encompassing most of the Rockies and ranges of the Intermountain West is indica ted for a slight risk of heavy snow throughout the forecast period. Additionally , a moderate risk is posted for the Northern Rockies for all of week-2, as well as a moderate risk of heavy snow for the Wasatch, and the Central and Southern R ockies, covering the period Dec 22-26. Along with heavy precipitation and sno w, high winds reaching hazardous criteria are also possible associated with this atmospheric river (AR) event. This is well indicated by the ECMWF and GEFS PETs which indicate at least a 20% chance of 3-day maximum wind speeds exceeding the 85th percentile for much of the CONUS throughout the week. Over the western CON US, enhanced winds are likely the result of deep troughing and AR over the West Coast, while periods of surface low pressure over the Plains and high pressure o ver the Southeast U.S. are the features enhancing winds elsewhere. A slight risk of high winds is posted for most of the western CONUS as well as the Northern a nd Central Plains and Great Lakes regions for all of week-2. The ECMWF PET is es pecially bullish, with probabilities exceeding 80% for much of the northwestern CONUS early in week-2, further backed by pattern recognition, warranting a moder ate risk of high winds for much of the Pacific Northwest, northern Great Basin, and Northern Rockies, also for the whole forecast period. FORECASTER: Danny Bar andiaran $$