US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 332 PM EDT Wed Sep 16 2020 Valid Saturday September 19 2020 - Wednesday September 23 2020 Hazards: - Heavy rain across portions of the Pacific Northwest and the Northern Great Basin, Wed, Sep 23. - Heavy rain across portions of the Lower Mississippi Valley and the Southern Plains, Sat-Wed, Sep 19-Sep 23. - Flooding possible across portions of the Southeast, the Mid-Atlantic, the Southern Appalachians, and the Tennessee Valley. - Flooding likely across portions of the Southeast. - Much above normal temperatures across portions of the Central Rockies and the Central/Northern Plains, Sat, Sep 19. - Much below normal temperatures across portions of the Great Lakes, the Ohio Valley, the Mid-Atlantic, the Central Appalachians, and the Northeast, Sat-Mon, Sep 19-Sep 21. - Much below normal temperatures across portions of the Great Lakes, Sat, Sep 19. - 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-Wed, Sep 22-Sep 23. - High winds across portions of mainland Alaska, Mon-Tue, Sep 21-Sep 22. - High winds across portions of the Alaska Panhandle, Tue, Sep 22. Detailed Summary: The medium range period (Saturday, Sep 19 - Wednesday, Sep 23) will feature an initially fairly amplified upper-level pattern, with a trough in the Great Lakes to Northeast. This upper trough and a cool Canadian surface high pressure system will cause fall-like below normal temperatures across those areas, shifting eastward through early next week. This could lead to the first frost or freeze in some areas of the Great Lakes region and interior Northeast, but mainly north of the major growing regions. Below normal temperatures extend southward all the way to the Southeast under the influence of the surface high. 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 Plains on Saturday toward the Great Lakes early next week, and above normal temperatures are forecast underneath it. Central/northern parts of the High Plains can expect temperatures nearing 90 on Saturday. Warmer than average temperatures should spread toward the Upper Mississippi Valley for the first half of next week, but temperatures in the 70s to mid-80s should not be hazardous. An upper-level trough is forecast to come in behind the ridge, helping cause modest rainfall particularly in the Northern Rockies over the weekend. Then, a potent upper low in the northeastern Pacific could bring heavy rain to northern portions of the Pacific Northwest by midweek. 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 are increasing probabilities 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, but a heavy rain hazard area was introduced to cover the potential threat, and will be refined in future issuances. After busy weather in the short range period, Alaska should have another round of active weather in the medium range. Showery conditions with locally modest rain totals are forecast for the Panhandle on Sunday as subtropical moisture is pulled into an initial frontal system. But the more notable weather will come from a large surface low pressure system that is forecast to move southeast from the Bering Sea Sunday across the Aleutians around Monday and through the Gulf of Alaska Tuesday and Wednesday. Gusty winds are possible over the Aleutians, but high winds may pose a greater threat across south-central Alaska, though it will depend on the exact low track. An area of high winds is also possible across southern coastal parts of the Panhandle on Tuesday. 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 Panhandle, and heavy rain is forecast Tuesday into Wednesday. Tate