US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 354 PM EST Fri Dec 18 2020 Valid Monday December 21 2020 - Friday December 25 2020 Hazards: - Heavy precipitation across portions of the Cascades, Mon, Dec 21. - Heavy precipitation across portions of northwestern Washington, Mon-Tue, Dec 21-Dec 22 and Fri, Dec 25. - Heavy precipitation across portions of the central Appalachians into the interior Northeast, Thu-Fri, Dec 24-Dec 25. - Heavy rain possible across portions of the interior Southeast into the southern Appalachians, Wed-Thu, Dec 23-Dec 24. - Heavy rain possible across portions of the Mid-Atlantic into New England, Wed-Fri, Dec 23-Dec 25. - Heavy rain possible across portions of the North Carolina coast, Thu-Fri, Dec 24-Dec 25. - Heavy snow across portions of the northern Rockies, Mon-Tue, Dec 21-Dec 22. - Heavy snow possible over northwestern Wyoming, Tue, Dec 22. - Flooding possible across portions of western Washington. - Flooding likely across portions of the western Washington. - High winds across portions of southeastern Wyoming, Mon, Dec 21. - Heavy precipitation across the Alaska Peninsula into southern Alaska, Mon-Wed, Dec 21-Dec 23. - Heavy precipitation across portions of the Alaska Panhandle into southern Alaska, Wed, Dec 23. - High winds across the Alaska Peninsula into southern Alaska, Mon-Tue, Dec 21-Dec 22. - Much below normal temperatures across much of the lower elevations of eastern Alaska, Mon-Tue, Dec 21-Dec 22. Detailed Summary: The active synoptic pattern over the northeastern Pacific will continue into the medium range period (Monday, Dec 20 - Friday, Dec 25) as additional moisture-laden and energetic frontal systems are forecast to impact the Pacific Northwest with heavy precipitation along the Cascades and northwestern Washington early next week. Further inland, heavy snow is expected to continue across portions of the northern Rockies in Idaho and western Montana on Monday before tapering off later on Tuesday as a developing low pressure system exits into the northern Plains. Portions of northwestern Wyoming could see heavy snow as well on Tuesday. Meanwhile, strong Chinook winds over southeastern Wyoming should gradually diminish on Monday as the previous low pressure system moves away into the upper Midwest. This will be quickly followed by the aforementioned low pressure system which should deliver a period of wintry precipitation across the upper Midwest to the Great Lakes Wednesday to Thursday. In the wake of this low pressure system, it appears that the Pacific Northwest will catch a break from the active weather as a strong ridge of high pressure aloft is forecast to build near the West Coast by the middle of next week. It appears that moisture from the next Pacific system will still be off the coast of the Pacific Northwest on Christmas Eve. However, chance of precipitation will increase on Christmas Day which may become heavy across northwestern Washington. Along the Gulf Coast, moisture from the Gulf of Mexico is forecast to return by the middle of next week. A cold front approaching from the Great Plains together with a developing low pressure wave could increase the chance of heavy rainfall for the interior Southeast, possibly up the Appalachians by later on Wednesday into Thursday. Models have been showing an increasingly amplified synoptic pattern moving into the East Coast during the latter part of next week. There is a possibility of widespread strong wind gusts together with wild swings in temperatures up and down the East Coast on Christmas Eve to Christmas Day if the upper trough and the associated front amplify like it is depicted by the GFS and the latest ECMWF. Heavy rain is also possible preceding the strong cold front, and could rapidly change over to snow behind the front. Any heavy rain falling over the interior Northeast on top of the recent snow pack would be a bad recipe for snow melt, which could result in flash flooding. Temperature-wise, the active zonal flow from the Pacific will result in above to well above normal temperatures across the northern tier states into the Plains with temperatures ranging anywhere from 10 to 25 degrees above normal early in the medium range period. Though anomalous, these temperatures are not expected to be hazardous. As the aforementioned ridge of high pressure builds near the West Coast, colder air from central Canada will be encouraged to dip into the Plains by next Wednesday into Thursday, resulting in below normal temperatures to return. Meanwhile, the active synoptic pattern over the northeastern Pacific will continue to direct large and energetic cyclones downstream toward Alaska during the medium range period. One such cyclone is forecast to bring widespread gale to storm force winds into the Alaska Panhandle on Monday. By Tuesday, much of the Alaska Peninsula into the southern portion of mainland will likely be engulfed with very gusty south to southeasterly winds along with heavy precipitation which will probably linger into Wednesday. In addition, some of the heavy precipitation is forecast to reach the Alaska Panhandle on Wednesday. There could be another cyclone approaching the Alaska Panhandle on Thursday but uncertainty remains high at this time. Farther inland across the lower elevations of eastern Alaska, much below average high and low temperatures are expected to continue into early next week, where temperatures are expected to reach as low as -35 to -40F. However, a general warm-up is forecast spread from southwest to northeast through Alaska from early to middle of next week. Kong