US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 333 PM EST Tue Dec 21 2021 Valid Friday December 24 2021 - Tuesday December 28 2021 Hazards: - Heavy precipitation across portions of California and the Pacific Northwest, Fri-Mon, Dec 24-Dec 27. - Heavy rain across portions of California, Fri, Dec 24. - Heavy snow across portions of California and the Pacific Northwest, Fri-Mon, Dec 24-Dec 27. - Heavy snow across portions of the Central Great Basin and California, Sat-Mon, Dec 25-Dec 27. - Heavy snow across portions of the Southern Rockies, the Central Rockies, the Central Great Basin, and the Southwest, Fri, Dec 24. - Flooding occurring or imminent across portions of the Pacific Northwest. - High winds across portions of the Central Plains, the Central Rockies, the Northern Plains, the Southern Rockies, the Southern Plains, and the Southwest, Fri, Dec 24. - Much below normal temperatures across portions of the Pacific Northwest, the Northern Rockies, and the Northern Great Basin, Sun-Tue, Dec 26-Dec 28. - Much below normal temperatures across portions of the Northern Plains and the Northern Rockies, Sat-Tue, Dec 25-Dec 28. - Heavy snow across portions of mainland Alaska, Sun, Dec 26. - High winds across portions of mainland Alaska, Fri, Dec 24. - Much below normal temperatures across portions of the Alaska Panhandle, Fri-Tue, Dec 24-Dec 28. Detailed Summary: During the upcoming medium range period (Friday, December 24 - Tuesday, December 28), persistent upper troughing will be locked over the western third of the lower 48, while mainly zonal flow or slight ridging remains prevalent across the central and eastern states. This pattern will maintain very unsettled weather from the Rockies westward as a series of weather systems rotates through the upper trough. There has been a lot of uncertainty with exactly how the details will unfold, but general consensus favors the most significant precipitation across the Pacific Northwest southward into northern and central sections of California. The heaviest amounts through the period are expected over the west-southwest facing slopes of the Cascades, Klamath mountains, coastal ranges of northern California and the Sierra. Some locations are likely to see several feet of snow in total by the early part of next week. Along with the unsettled conditions, there's a lot of cold air associated with this system, so snow levels will tend to be relatively low. And by late in the weekend into early next week, snow levels across parts of the Pacific Northwest will be near sea level, so accumulating snow is possible across the major cities west of the Cascades. Right now, amounts are not likely to be too heavy, but may pose driving hazards as this is likely the first snow of the season for many of these areas. Elsewhere in the west, a strong southern stream short wave moving inland Friday will bring locally heavy rains to southern California and bring widespread rain/high elevation snow into the southwestern states and southern/central Rockies. Strong westerlies through the mid layers of the atmosphere and low pressure developing in the lee of the Rockies associated with this system will bring locally windy conditions during Friday, primarily focused over sections of southeastern Wyoming and eastern New Mexico, but impacts may be felt east of the Colorado Rockies as well. Across the north-central states, a very cold Arctic air mass will build from western Canada into northern Montana later this week, then spread south and eastward to encompass much of Montana and the Dakotas(especially North Dakota) by early next week. High temperatures over the weekend will mostly range in the single digits, with below zero readings across parts of northern Montana. Lows will drop into the teens to over 20 degrees below zero (upwards of 20-30 degrees below average). Arctic air will also gradually spill westward into parts of northern/central Idaho and eastern Washington and Oregon, resulting in temperatures well below freezing during the early part of next week. Across Alaska, the same Arctic air mass impacting the north-central part of the lower 48 will be deeply entrenched over the Alaska Panhandle through much of the period. Temperatures will average well below normal, with the most anomalous readings likely across the southern half to two-thirds of this region. Farther north, there will likely be one more day (Friday) with strong gap winds off the south-central mainland, most prominent between Kodiak Island and Kenai Peninsula. Finally, the models are in reasonable agreement that a storm system and associated cold front will move quickly across interior sections of the mainland Sunday. Deep moisture preceding the front will support an area of heavy snow across the Seward Peninsula, southern part of the Brooks Range and eastward toward the Fairbanks area. Snow will likely be accompanied by strong winds, leading to blowing snow and local blizzard conditions. Klein