US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 338 PM EDT Thu Sep 17 2020 Valid Sunday September 20 2020 - Thursday September 24 2020 Hazards: - Heavy rain across portions of the Pacific Northwest and the Northern Great Basin, Wed-Thu, Sep 23-Sep 24. - Heavy rain across portions of the Southern Plains, the Lower Mississippi Valley, and the Southeast, Sun-Thu, Sep 20-Sep 24. - Flooding possible across portions of the Southeast, the Mid-Atlantic, the Southern Appalachians, and the Tennessee Valley. - Flooding occurring or imminent across portions of the Southeast. - Flooding likely across portions of the Southeast. - Much below normal temperatures across portions of the Great Lakes, the Ohio Valley, the Central Appalachians, the Mid-Atlantic, and the Northeast, Sun-Tue, Sep 20-Sep 22. - Heavy precipitation across portions of mainland Alaska, Mon-Tue, Sep 21-Sep 22. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Tue-Wed, Sep 22-Sep 23. - Heavy rain across portions of the Alaska Panhandle, Tue-Thu, Sep 22-Sep 24. - High winds across portions of the Alaska Panhandle, Tue-Wed, Sep 22-Sep 23. Detailed Summary: The medium range period (Sunday, Sep 20 - Thursday, Sep 24) will feature an initially fairly amplified upper-level pattern, with a trough in the Northeast. This upper trough and a cool Canadian surface high pressure system will cause fall-like below normal temperatures across the East through early next week. This could lead to the first frost or freeze in some areas of the Lower Great Lakes region and interior Northeast, but mainly north of the major growing regions. A hazard area was drawn where temperatures could be below around 40 degrees, but below normal temperatures extend southward all the way to the Southeast under the influence of the surface high. Some record lows could be set, especially for low maximum temperatures, but the temperatures will not be considered hazardous. Given the placement of the high in the East and lower pressure offshore in the Atlantic (due to the remnants of Sally followed by Teddy moving northward), high wave heights are possible in the western Atlantic. Significant waves should remain offshore, but parts of the Atlantic coast may have the potential for beach erosion and rip currents through the first part of next week. Meanwhile farther west, an upper-level ridge of high pressure is expected to shift from the Upper Midwest toward the Great Lakes early next week, with additional ridging building for the north-central U.S. and across the Great Basin to northern Rockies later in the week. Underneath, high temperatures should be around 10 to 15 degrees above average centered in the Central/Northern Plains through the period, but temperatures in the 70s to mid-80s are not expected to be hazardous. By midweek, a potent upper low in the northeastern Pacific could bring heavy rain to northern portions of the Pacific Northwest. Far south of the main jet stream, a tropical area of low pressure is expected to meander in the Bay of Campeche/western Gulf of Mexico over the next several days, and there is a high probability from the National Hurricane Center that it should become a tropical cyclone. It is forecast to cause heavy rain especially over water, but potentially along the western and central Gulf Coast as well. Uncertainty remains with how much rain will fall along the Texas and Louisiana coastlines as well as the timing, but a heavy rain hazard area is in place to cover the potential threat. After busy weather in the short range period, Alaska should have another round of active weather in the medium range. A large surface low pressure system is forecast to move southeast from the Bering Sea Sunday across the Aleutians around Monday and across the Gulf of Alaska through Thursday. Gusty winds are possible over the Aleutians, as well as potentially across south-central Alaska, though it will depend on the exact low track. High winds are most likely for southern coastal parts of the Panhandle late Tuesday into early Wednesday. Another threat with this system will be heavy precipitation from the Alaska Peninsula toward the Kenai Peninsula for Monday/Tuesday, shifting eastward Tuesday/Wednesday. Snow could fall in the higher elevations. Precipitation should remain rain in the southeastern Panhandle, and heavy rain is forecast Tuesday through Thursday. Tate