US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 250 PM EST Mon Dec 06 2021 Valid Thursday December 09 2021 - Monday December 13 2021 Hazards: - Heavy rain across portions of the Lower Mississippi Valley, the Central Appalachians, the Tennessee Valley, the Southern Appalachians, the Great Lakes, and the Ohio Valley, Fri-Sat, Dec 10-Dec 11. - Heavy snow across portions of the Pacific Northwest and the Northern Great Basin, Thu-Sun, Dec 9-Dec 12. - Heavy snow across portions of the Central Plains, the Central Rockies, the Central Great Basin, the Southern Rockies, California, and the Southwest, Thu, Dec 9. - Heavy snow across portions of the Northern Rockies and the Northern Great Basin, Sat-Sun, Dec 11-Dec 12. - Heavy snow across portions of the Great Lakes, the Upper Mississippi Valley, and the Northern Plains, Fri, Dec 10. - High winds across portions of the Southern Rockies and the Southern Plains, Fri, Dec 10. - Heavy precipitation across portions of mainland Alaska, Thu, Dec 9. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Fri, Dec 10. - High winds across portions of mainland Alaska and the Aleutians, Thu-Sat, Dec 9-Dec 11. - Much below normal temperatures across portions of mainland Alaska and the Aleutians, Sat-Mon, Dec 11-Dec 13. Detailed Summary: A low pressure system moving through the Rockies on Thursday and ejecting into the Plains by Friday will spread a variety of weather hazards across portions of the U.S. for the first half of the medium range period. Amplified troughing through the West on Thursday will bring colder temperatures and lowering snow levels to spread the potential for heavy snowfall across the mountains of the West. Moderate to significant snowfall totals are possible on Thursday across the Washington/Oregon cascades, the Sierras, and into the higher terrain of the Intermountain West and central Rockies. By Friday, a deepening area of low pressure is expected to develop at the surface with a period of gusty winds likely on the backside of the low across portions of the southern High Plains. The low should be rather progressive as it lifts into the Upper Midwest by Saturday. On the north/cold side of the low, heavy snow appears possible on Friday across portions of the Upper Mississippi Valley from roughly southern Minnesota to northern Wisconsin, including the Minneapolis/St. Paul metro area. To the east, ample moisture from the Gulf of moisture will stream northward ahead of the associated cold front to fuel an expansive heavy rainfall threat across much of the Tennessee Valley to the lower Ohio Valley and central Applachians. Several inches of rain are possible on Saturday. A series of systems into the West through the weekend and into early next week will keep the potential for heavy snow in the forecast across the Cascades and also into parts of the northern Rockies. Moderate to heavy rainfall is also possible across the coastal Pacific Northwest but given the dry conditions across that region lately it's likely to be more of a beneficial rainfall rather than presenting any significant hazard. In Alaska, a powerful storm system will shift from the Bering Sea into the northern Gulf Thursday and into the weekend bringing a significant threat for winds and waves to the Aleutians, Alaska peninsula, and parts of coastal western Alaska. The system should weaken gradually as it shifts into the northern Gulf on Friday, but favorable moisture transport will continue to support a threat for heavy rain/mountain snow across portions of the southern Coast and especially the Panhandle late this week. In the wake of the system, much below normal temperatures will overspread much of the state (with the exception of the North Slope region). Daytime highs 20-30+ degrees below normal are possible, especially for southwest Alaska. The guidance continues to show potential for another storm system to enter the Bering Sea and impact parts of the Aleutians late this weekend into early next week, but there is enough uncertainty remaining that no hazards were depicted for this system today. This will need to continue to be monitored as the models come into better agreement on any potential hazards associated with this next storm. Santorelli