US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 341 PM EST Thu Nov 11 2021 Valid Sunday November 14 2021 - Thursday November 18 2021 Hazards: - Heavy precipitation across portions of the Pacific Northwest and the Northern Great Basin, Sun-Mon, Nov 14-Nov 15. - Heavy rain across portions of the Pacific Northwest, Sun-Mon, Nov 14-Nov 15. - Flooding possible across portions of the Pacific Northwest. - Flooding possible across portions of the Pacific Northwest. - Flooding occurring or imminent across portions of the Southeast. - Flooding occurring or imminent across portions of the Southeast. - Flooding occurring or imminent across portions of the Southeast. - Flooding likely across portions of the Pacific Northwest. - Flooding likely across portions of the Pacific Northwest and the Northern Great Basin. - High winds across portions of the Central Plains, the Northern Plains, and the Northern Rockies, Tue, Nov 16. Detailed Summary: The upcoming medium range forecast period (Sunday, November 14th - Wednesday, November 17th) continues the very wet pattern along the Pacific Northwest through Monday, before unsettled conditions shift into the Central U.S. toward midweek. Over the Pacific Northwest, guidance maintains general agreement regarding the arrival of Eastern Pacific troughing and associated frontal system off the British Columbia coast days 3-4. Ahead of the southeast diving cold front in British Columbia, southwesterly flow will focus warm advection and moisture flux overhead to produce moderate to heavy rainfall and elevation mixed precipitation beginning Sunday. As usual, the highest rainfall rates will be tied to favorable terrain along the Coastal and Cascade Ranges. However, the very wet antecedent soil conditions throughout the region (including the valleys) make it more vulnerable to runoff, which justifies the slight extension of the Heavy Rain area eastward through Monday. High snow levels will initially keep mixed precipitation in the forecast for most of the Coastal and Cascade Ranges, with the best snow chances relegated to the peaks of the Cascades. However, the passage of the cold front on Monday will decrease snow levels and change the precipitation mode to predominantly snow in the mountains. As the frontal system continues east across the Intermountain West, snow chances will also ramp up over the Northern Rockies, with moderate accumulations possible. Beginning Tuesday, low pressure is forecast to deepen as it ejects eastward across the Northern Plains. The tightening pressure gradient and downsloping flow will facilitate hazardous gusty winds across the High Plains into Wednesday, before high pressure builds in behind the system. Meanwhile over the Midwest, a shortwave trough over the Great Lakes is forecast to slide southeast and reinforce mean troughing over the eastern half of the U.S. on Sunday. An associated cold front will sweep across the eastern half of the CONUS and inject cool continental air southward, which translates to high temperatures 10 degrees below normal early next week. No hazardous precipitation is anticipated with this activity, although cool northwesterly flow atop the uncovered Great Lakes will favor periods of lake enhanced precipitation in the Upper Midwest/Northeast. Moreover, the frontal passage in New England early next week may support mountain snows in the peaks of the Adirondack, Green, and White Mountains, but hazardous weather is not expected. Eventually toward days 6-7, the Pacific Northwest system will spread rain chances over the Midwest as Gulf inflow increases ahead of the cold front, which will be monitored in future hazards updates. Temperature wise, well above average warmth will reside over the western half of the U.S. to begin next week, and a few overnight low records may be threatened along the West Coast and High Plains ahead of the front. The arrival of the cold front through the West and Central U.S. will quickly moderate temperatures to slightly below normal, however. In the eastern half of the U.S., initial cool temperatures beneath a Canadian airmass will warm as southwesterly flow ramps up ahead of the aforementioned Pacific system. Overall however, no hazardous temperatures are anticipated. Generally quiet weather continues over Alaska. Some of the rain associated with the aforementioned British Columbia trough may spill into the southern Alaska Panhandle later this weekend, but the highest precipitation totals are expected to stay south of the area. Afterwards, guidance advertises the general return of a wet pattern the over Panhandle toward the end of the medium range with low pressure off lingering the Gulf of Alaska. Additionally, a cold period is expected for Southwest Alaska early next week, which may gradually build in with high pressure overhead. In general, high temperatures over West-Central Alaska will be below normal through much of the medium range. Asherman