404 FXUS21 KWNC 291936 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EST December 29 2025 SYNOPSIS: A significant and rapid mid-level pattern change is predicted across the Pacific during the week-2 period. While this favors a warming trend across Alaska, model solutions vary regarding the downstream response across the contiguous U.S. (CONUS) making for a low confidence and challenging hazards outlook. Continued onshore flow across the western CONUS early in the period favors increased chances of heavy precipitation (coastal rain and high elevation snow) near the West Coast. East of the Rockies, high latitude blocking combined with periodic shortwave disturbances could lead to a more active weather pattern depending on where various features line up. HAZARDS Slight risk of heavy precipitation across the west coast of the CONUS, Tue-Thu, Jan 6-8. 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, Tue-Thu, Jan 6-8. Slight risk of heavy snow across portions of the eastern Great Lakes, Northeast, and Central Appalachians, Tue-Thu, Jan 6-8. Slight risk of high winds across much of the CONUS west of the Rockies, Tue-Thu, Jan 6-8. Slight risk of much below-normal temperatures across portions of southwestern Mainland Alaska and the Alaska Peninsula, Tue-Thu, Jan 6-8. Slight risk of high winds across portions of the Alaska Peninsula, southern Mainland Alaska, and southeastern Alaska, Tue-Thu, Jan 6-8. DETAILED SUMMARY FOR THURSDAY JANUARY 01 - MONDAY JANUARY 05: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR TUESDAY JANUARY 06 - MONDAY JANUARY 12: 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 ridging over the western CONUS and eastern Alaska by the end of week-2. This would be consistent with a weakening negative phase of the Pacific North American (-PNA) pattern. While the 0z GEFS also depicts this transition to some degree, it is slower and more west-based with the trough and ridge features at the end of the period compared to the ECMWF and Canadian. Troughing near the West Coast of the CONUS at the outset of the period favors continued chances of heavy precipitation. 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 early in week-2, with greater than 40 percent chances for exceeding the 85th percentile over southern California. Uncalibrated guidance from the 0z GEFS favors a stronger moisture surge into southern California due to a more southward displacement of the amplified trough. However, the 0z ECMWF and Canadian ensembles favor the bulk of the moisture over the Pacific Northwest. Therefore, a broad slight risk for heavy precipitation is posted across the entire West Coast, valid Jan 6-8, with a corresponding slight risk of heavy snow across higher elevations of the Cascades, Klamath, and Sierra Nevada Mountains. 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 probabilities farther west precluding an extension of the hazard. A slight risk of high winds is also posted across parts of the western CONUS, Jan 6-8, with the ECMWF PET depicting a robust wind signal across the Northwest associated with the strongest onshore flow early in week-2. However, the much weaker GEFS adds to the uncertainty supporting only a slight risk. While enhanced precipitation may continue across the Northwest later in week-2 based on the ECMWF Integrated Vapor Transport (IVT) tool, the potential for a more amplified ridge over the West as depicted in the ECMWF and Canadian ensembles would favor less precipitation. As a result, the associated hazards are not extended later into week-2 at this time. Further downstream across the CONUS, multiple shortwave disturbances are likely to propagate through the mean flow. Many of today's deterministic solutions are not as robust regarding an initial northern stream surface low at the outset of the period (Jan 6) compared to yesterday, although probabilities for snowfall greater than 4 inches during the first 3 days of the period exceed 20 percent in both the 0z ECMWF and GEFS ensembles across parts the Northeast and eastern Great Lakes likely tied to another system around day-10 (Jan 8). This supports maintaining the slight risk for heavy snow over these areas, extending into the Central Appalachians, Jan 6-8. Further south, the ECMWF and GEFS PETs depict at least a 20 percent chance 3-day precipitation totals exceed 1-inch over parts of the Lower Mississippi Valley, Tennessee Valley, and Southeast, although the signals are weaker than yesterday in percentile space. Based on continuity, a slight risk of heavy precipitation remains in place, Jan 6-10. The northward trajectory of this moisture is uncertain, although a substantial high-latitude blocking ridge predicted over northeastern North America could result in a more significant synoptic system across the eastern half of the CONUS toward the second half of week-2 depending on the alignment and amplitude of shortwave features. Surface low pressure forecast over the Gulf of Alaska and relatively higher pressures over Mainland Alaska favor a strong pressure gradient over southern Alaska. This results in elevated chances for episodes of high winds across the Alaska Peninsula eastward 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 6-8. The mid-level pattern transition favors a moderation of persistently cold temperatures across Alaska. While signals in the ECMWF and GEFS PETs remain elevated over southwestern Alaska, actual temperatures are becoming less likely to reach hazards thresholds, with positive temperature anomalies emerging over most of the state by the end of the period. As a result, the moderate risk for much below normal temperatures is discontinued, with a slight risk posted across southwestern Mainland Alaska through Jan 8. Some interior areas may experience minimum temperatures below -10 deg F, although the Alaska Peninsula and southern coast are more likely to have minimum temperatures in the positive single digits or teens. 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. FORECASTER: Thomas Collow $$