US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 428 PM EDT Wed Sep 09 2020 Valid Saturday September 12 2020 - Wednesday September 16 2020 Hazards: - Heavy rain across portions of the Pacific Northwest, Mon-Tue, Sep 14-Sep 15. - Heavy rain across portions of the Northeast, the Central Appalachians, the Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, the Southern Plains, and the Ohio Valley, Sat-Sun, Sep 12-Sep 13. - Heavy rain across portions of the Southeast, the Mid-Atlantic, and the Southern Appalachians, Sat-Mon, Sep 12-Sep 14. - Heavy rain across portions of the Southeast, the Mid-Atlantic, and the Southern Appalachians, Mon-Wed, Sep 14-Sep 16. - Flooding possible across portions of the Southern Plains. - Much above normal temperatures across portions of California, the Central Great Basin, the Pacific Northwest, and the Northern Great Basin, Sat-Sun, Sep 12-Sep 13. - Much above normal temperatures across portions of the Central Great Basin, the Northern Rockies, the Northern Great Basin, and the Northern Plains, Sat-Mon, Sep 12-Sep 14. - Much above normal temperatures across portions of the Central Plains and the Northern Plains, Mon-Tue, Sep 14-Sep 15. - Heavy rain across portions of mainland Alaska and the Aleutians, Sun-Mon, Sep 13-Sep 14. - Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Tue-Wed, Sep 15-Sep 16. Detailed Summary: The medium range period (Sat Sept. 12 - Tues Sept. 16) features a gradual warm up across the Rockies and Nation's Heartland. After the significant cold snap and heavy snow blanketing the Rockies through mid-week, the upper low is forecast to make its way east into the Plains to start the weekend, then open up into a shortwave trough over the Great Lakes by Sunday. Moderating temperatures look to transpire across the central Rockies and Plains throughout the weekend. By early next week, upper level ridging returns to the Intermountain West, resulting in the arrival of much above normal temperatures across the northern Rockies and Plains. The East Coast may see a slight reprieve from being at the mercy of a large subtropical high over the northwest Atlantic as a pair of cold fronts swing through the Northeast early next week, but in general, the upper level ridge looks to stick around just offshore, keeping warm and humid conditions in the forecast for most of the period in the Southeast. Precipitation-wise, periods of rain in the Upper Midwest early Saturday but the bulk of the heavy rainfall is forecast to occur on Friday. In the Southeast, southeasterly flow tapping into Atlantic and Gulf moisture sets up a scenario where several days worth of precipitation is likely in the southern Appalachians. Rainfall could become excessive at times, which combined with above normal soil moisture content may lead to flooding opportunities next week. Another area that could experience upslope flow is West Texas where low level winds and elevated moisture levels foster persistent periods of rainfall this weekend and into early next week. In the Pacific Northwest, well above normal temperatures and dry conditions this weekend gives way to a welcomed cooler and wetter regime early next week. Rainfall rates will need to be monitored closely, however, as heavier rainfall rates in burn scarred areas could trigger debris flows. In Alaska, a potent low pressure system over the North Pacific will deepen more as the storm moves passes over the Aleutians and into the Bering Sea early next week. Latest guidance has backed off on wind speeds over the last 24 hours, so have taken high winds out of the forecast for now. In addition, a plume of moisture associated with the storm moves into parts of the the Aleutians and the southwest mainland this weekend. By next week, a new wave of low pressure is forecast to develop in the Gulf of Alaska that could have a moisture source that taps into the subtropics and as far west as West Pacific typhoon activity. This would set the stage for a heavy rainfall, and potentially mountain snow, event next week. There is still plenty of uncertainty in days 6-7 but this set up does bear watching in the days to come. Mullinax