US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 400 PM EST Tue Nov 09 2021 Valid Friday November 12 2021 - Tuesday November 16 2021 Hazards: - Heavy rain across portions of the Mid-Atlantic, the Northeast, and the Pacific Northwest, Fri, Nov 12. - Heavy snow across portions of the Pacific Northwest and the Northern Great Basin, Fri, Nov 12. - Flooding occurring or imminent across portions of the Southeast. - Flooding occurring or imminent across portions of the Southeast. - High winds across portions of the Central Plains, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Northern Plains, Fri, Nov 12. - Heavy precipitation across portions of the Alaska Panhandle, Fri, Nov 12. Detailed Summary: The upcoming medium range forecast period (Friday, November 12th - Tuesday, November 16th) features scattered areas of hazardous precipitation and wind to begin this weekend over the CONUS, before a period of generally calm conditions set in afterwards. Guidance is in good agreement on the pattern on day 3, including a deep closed low and strong associated frontal system pivoting northeast across the Great Lakes into Canada. A period of strong winds is possible across the Northern Plains on Friday as high pressure builds behind the low, where some blowing snow concerns may arise over portions of the Northern Tier atop freshly fallen snowfall. In the warm sector over the Northeast, an influx of Atlantic moisture ahead of an approaching cold front will facilitate efficient rainfall rates, although the progressive cold front should relegate the excessive rain threat to the 12th before cool and dry air sets in overhead. While much of the area will remain dry afterwards, the cold advection behind the front supports a favorable pattern for multiple days of potential lake effect snow offshore Lake Michigan, Erie, and Ontario. Moreover, High Plains shortwave activity is forecast to eventually slide southeast by early next week and force a fresh injection of cool air southward, which may further enhance lake effect snow chances. Otherwise, the precipitation forecast remains on track over the Pacific Northwest on Friday for a period of moderate to heavy rainfall and mountain snow, as onshore flow strengthens with plentiful Pacific moisture to work with. The next possibility of enhanced rainfall and mountain snow will appear later this weekend as troughing off the British Columbia coast approaches and pulls another plume of Pacific flow inland, which will be monitored in subsequent hazards updates. With respect to temperatures, no hazardous conditions are anticipated at this time. Rising heights along and west of the Continental Divide will generally keep high temperatures in the western CONUS 10-15 degrees above average through the medium range period, before well above average warmth creeps into the Plains toward day 7. Overnight lows will remain quite warm as well, and a few locations along the West Coast may challenge their record over the medium range. Strong southerly flow on the 12th will also support well above average warmth over the Mid-Atlantic and Northeast, where some overnight low records could similarly fall. However, the cool weather quickly takes over beyond Friday in the eastern CONUS as a series of cold fronts maintain high temperatures 10-15 degrees below average. After a quiet period of hazardous weather for Alaska, heavy mixed precipitation is possible over the Panhandle from Yakutat southward on Friday as potent low pressure approaches the coastline and moist southwesterly flow ascends the terrain. The deep pressure gradient will support locally hazardous gap wind flows as well on Friday, although the small scale nature of these gusty winds precludes a hazard area. A cooling trend will set in over the southwest part of the state as high pressure builds in on the backside of the low pressure system. High temperatures will be well below normal through much of the medium range, although hazardous conditions are not expected. Asherman