US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 411 PM EDT Tue Sep 08 2020 Valid Friday September 11 2020 - Tuesday September 15 2020 Hazards: - Heavy rain across portions of the Central Appalachians, the Tennessee Valley, the Southern Plains, the Southern Appalachians, the Great Lakes, and the Ohio Valley, Sun-Mon, Sep 13-Sep 14. - Heavy rain across portions of the Central Plains, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Northern Plains, Fri-Sat, Sep 11-Sep 12. - Heavy rain across portions of the Southeast, the Mid-Atlantic, and the Southern Appalachians, Sun-Tue, Sep 13-Sep 15. - Flooding possible across portions of the Southern Plains. - Flooding occurring or imminent across portions of the Lower Mississippi Valley. - Much above normal temperatures across portions of the Central Great Basin, the Northern Plains, the Northern Rockies, California, the Northern Great Basin, and the Pacific Northwest, Fri-Mon, Sep 11-Sep 14. - Much above normal temperatures across portions of California, the Pacific Northwest, and the Northern Great Basin, Fri-Sat, Sep 11-Sep 12. - Much above normal temperatures across portions of the Central Plains, the Northern Plains, and the Northern Rockies, Sat-Mon, Sep 12-Sep 14. - Heavy rain across portions of mainland Alaska and the Aleutians, Sun-Mon, Sep 13-Sep 14. - High winds across portions of mainland Alaska and the Aleutians, Sun-Mon, Sep 13-Sep 14. Detailed Summary: The theme of the medium range period (Fri Sept. 11 - Tues Sept. 15) can be summarized in one word: transition. 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. Friday will likely still be quite cool in parts of the central Plains and Rockies with moderating temperatures into the weekend. The Pacific Northwest continues to deal with well above normal temperatures into the start of the weekend but a new storm system approaching the region ushers in a welcomed cooler temperature regime early next week. Unfortunately, the warm start to the week will also mean continued dry and hot conditions. Fire weather will continue to be favorable, especially in portions of Southern California where winds very low humidity levels and blustery winds take shape. 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, a low pressure system swinging through the Midwest may generate heavy rainfall amounts across the region Friday and into early this upcoming weekend. 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. It is possible rainfall could become excessive at times, which combined with above normal soil moisture content could lead to flooding into early next week. Another area that could experience upslope flow is West Texas where low level winds and elevated moisture levels could lead to persistent periods of rainfall this weekend and into early next week. For 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. The deep low is forecast to produce an area of high winds over parts of the Aleutian Islands and the Alaska Peninsula on Sunday and Monday. In addition, a plume of moisture associated with the storm moves into parts of the the Aleutians and the southwest mainland. The system will produce an area of heavy rain from parts of the Alaska Peninsula and the Southwestern mainland that could extend into the Gulf of Alaska Coast on Monday, but spread in ensemble guidance makes the precipitation amounts uncertain at this time there. Mullinax