US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 357 PM EST Fri Nov 12 2021 Valid Monday November 15 2021 - Friday November 19 2021 Hazards: - Heavy precipitation across portions of the Pacific Northwest and the Northern Great Basin, Mon, Nov 15. - Heavy rain across portions of the Pacific Northwest, Mon, Nov 15. - Flooding possible across portions of the Pacific Northwest. - Flooding possible across portions of the Pacific Northwest. - Flooding possible across portions of the Pacific Northwest. - Flooding occurring or imminent across portions of the Pacific Northwest and the Northern Great Basin. - 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. - Flooding likely across portions of the Middle Mississippi Valley and the Pacific Northwest. - High winds across portions of the Central Rockies, the Central Plains, the Northern Plains, the Northern Rockies, and the Northern Great Basin, Mon-Tue, Nov 15-Nov 16. - High winds across portions of the Central Plains, the Upper Mississippi Valley, and the Northern Plains, Tue-Wed, Nov 16-Nov 17. - Much below normal temperatures across portions of mainland Alaska, Mon-Thu, Nov 15-Nov 18. Detailed Summary: The upcoming medium range forecast period (Monday, November 15th - Thursday, November 18th) continues the very wet weather along the Pacific Northwest on Monday, before unsettled conditions shift into the Central U.S. toward midweek. Over the Pacific Northwest, guidance highlights the arrival of Eastern Pacific troughing and associated cold front off the British Columbia coast on Monday. 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 through Monday. As usual, the highest rainfall rates will be tied to favorable terrain along the Coastal, Cascade, and Olympic Ranges. However, with very wet antecedent soil conditions and localized burn scar areas throughout the region, even spillover precipitation from the terrain could cause runoff issues. 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 will decrease snow levels and change the precipitation mode to predominantly snow in the mountains. Moderate snowfall will eventually spill into the Northern Rockies as well, but is anticipated to remain below hazard criteria. Precipitation aside, the approach and amplification of the upper trough later on Monday is forecast to initiate lee cyclonegenesis along the slopes of the Canadian Rockies. The accompanying pressure gradient will produce increasingly gusty winds beginning Monday over the Northern Rockies, before spreading eastward with the low into the Northern Plains Tuesday/Wednesday. Strong wind gusts below hazard levels are possible over the Upper Midwest Great Lakes Wednesday/Thursday as the deep surface low skirts to the north, too. Meanwhile in the east, a shortwave trough will deepen and eventually close off as it sweeps across the the Northeast Monday/Tuesday with an attendant cold front. Rain and mountain snows are possible with the passage of this system, including lake enhanced precipitation for locations offshore Lake Erie and Ontario. Afterwards, the next weather-maker (aforementioned Pacific system) is forecast to arrive over the eastern half of the CONUS around midweek. Moisture streaming northward from the Gulf of Mexico ahead of the system will increase rain chances along a sprawling cold front from the western Gulf states into the Northeast, where rain totals should hover around light to moderate. Temperature wise, a large area of well above average warmth (10-25 degree anomalies) will reside over the western half of the U.S. to begin next week, and a few temperature records may be threatened along the West Coast and Plains ahead of the front. The arrival of the cold front through the West and Central U.S. will quickly drop temperatures to slightly below normal. In contrast to the West, the eastern half of the U.S. will begin with cool temperatures (highs 5-15 degrees below average) next week, which quickly warm to above average around midweek given the warm advection regime ahead of the cold front. Toward the end of next week, temperatures around the CONUS should largely reset to around normal following a trend toward a more zonal (west-east) flow pattern aloft. Alaska will remain largely dry, but cold throughout the medium range period. Guidance continues to advertise low pressure migrating out of the Bering Sea toward the Gulf of Alaska days 4-5, which will spread precipitation chances over the Panhandle. Strengthening high pressure on the back side of the low will keep cold temperatures locked over West/Southwest Alaska through next week. While spread remains regarding strength of the upcoming pattern, the possibility of high temperatures 15-30 degrees below normal in some locations prompted the addition of a Much Below Normal area for the 15th-18th. Asherman