US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 203 PM EST Fri Nov 26 2021 Valid Monday November 29 2021 - Friday December 03 2021 Hazards: - Heavy precipitation across portions of the Pacific Northwest and the Northern Great Basin, Tue-Wed, Nov 30-Dec 1. - Heavy rain across portions of the Pacific Northwest, Tue-Wed, Nov 30-Dec 1. - Flooding occurring or imminent across portions of the Pacific Northwest. - Flooding likely across portions of the Pacific Northwest and the Northern Great Basin. - Heavy precipitation across portions of mainland Alaska, Mon, Nov 29. - High winds across portions of mainland Alaska, Mon, Nov 29. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Tue-Wed, Nov 30-Dec 1. - Much below normal temperatures across portions of mainland Alaska, Mon-Tue, Nov 29-Nov 30. - Much below normal temperatures across portions of mainland Alaska, Mon-Fri, Nov 29-Dec 3. Detailed Summary: During the medium range period (Monday, November 29th - Friday, December 3rd) much of the impactful activity over the CONUS will be isolated to the Pacific Northwest as an atmospheric river soaks the region with an influx of tropically-sourced moisture. The moderately strong atmospheric river is forecast to move onshore Tuesday afternoon ahead of a progressing warm front. Though snow levels over the Pacific Northwest will initially be low enough to support snow and mixed precipitation over the northern Washington Cascades, warm air behind the front will quickly raise snow levels and restrict a majority of the liquid precipitation to fall as rain only throughout much of the region, save for at the highest elevations. However, a cold front expected to move onshore Wednesday will force snow levels to plummet, allowing for a greater coverage of moderate snowfall and mixed precipitation over the northern Washington Cascades and the Olympics. In the neighboring Northern Rockies, a tight surface pressure gradient is forecast to set up on the lee side of the mountains Tuesday into Wednesday, generating isolated high winds with gusts up to 50 mph to the east of the Lewis Range in northwest Montana. Additionally, moisture from the previously discussed atmospheric river is expected to reach the region Wednesday, allowing for light mountain snow accumulations over the Lewis Range, the Absaroka Range, and the Bighorn Mountains through Thursday. Further east, a low pressure/frontal system passing through southern Quebec may deliver light lake effect and mountain snow to the Upper Midwest, Upstate New York, and interior New England Wednesday and Thursday. Temperature-wise, a cool airmass is expected to pass through the eastern half of the country at the start of the period, driving daily highs and lows slightly below normal on Monday and Tuesday before rebounding back to near normal for the remainder of the week. Conversely, temperatures out west will remain well above normal throughout the period as a building upper-level ridge and pair of passing warm fronts at the surface keep temperatures stably warm. This is particularly true for the Northern and Central Plains where daily highs may reach 20 to 25 degrees above average on Monday, Wednesday, and Thursday. In Alaska, a deep low pressure system is forecast to make its way through the Gulf early next week, bringing high winds in excess of 55 mph and heavy precipitation to Kodiak Island, Katma National Park, and the Kenai Peninsula on Monday. As the system progresses further east it will draw a significant amount of lower latitude moisture northward before redirecting it into the Panhandle and adjacent southern mainland. With liquid precipitation in excess of 2 inches forecast to move onshore, heavy coastal rain and inland mountain snow is expected to fall over these regions Tuesday into Wednesday. With regard to temperature, frigid below average highs and lows are forecast for much of the mainland throughout the period due to persistent surface high pressure systems over the East Siberian Sea funneling icy air southward. The southwestern, western, and Interior portions of the state are expected to experience the most severe temperature anomalies, with overnight lows on track to plummet 20 to 30 degrees below normal. With nighttime temperatures falling to and below -30F in some areas, residents should limit time outdoors and take proper precautions to prevent the onset of frostbite and/or hypothermia. Warmer air is expected to arrive in the Interior mainland on Wednesday to help bring temperatures back up closer to normal, however, the other afflicted regions will have to wait until at least next weekend to experience any relief from the bitter cold. Zavadoff