US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 424 PM EDT Tue Sep 15 2020 Valid Friday September 18 2020 - Tuesday September 22 2020 Hazards: - Heavy rain across portions of the Southeast and the Mid-Atlantic, Fri, Sep 18. - Flooding possible across portions of the Southeast, the Lower Mississippi Valley, and the Tennessee Valley. - Flooding likely across portions of the Southeast and the Lower Mississippi Valley. - Much above normal temperatures across portions of the Central Great Basin, the Central/Northern Rockies, and the Central/Northern Plains, Fri, Sep 18. - Much above normal temperatures across portions of the Central Rockies and the Central/Northern Plains, Fri-Sat, Sep 18-Sep 19. - Much below normal temperatures across portions of the Great Lakes, the Mid-Atlantic, the Northeast, the Central Appalachians, and the Ohio Valley, Sat-Mon, Sep 19-Sep 21. - Much below normal temperatures across portions of the Great Lakes, Fri-Sat, Sep 18-Sep 19. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Fri, Sep 18. - Heavy precipitation across portions of mainland Alaska and the Aleutians, Mon-Tue, Sep 21-Sep 22. - Heavy rain across portions of the Alaska Panhandle, Sun, Sep 20 and Tue, Sep 22. - High winds across portions of mainland Alaska, Mon-Tue, Sep 21-Sep 22. Detailed Summary: The medium range period (Friday, Sep 18 - Tuesday, Sep 22) will first feature the remnants of Hurricane Sally moving through the Southeast before combining with a cold front off the U.S. East Coast likely by Saturday morning. While there remains some uncertainty with the speed at which Sally moves eastward, it appears that Friday could still see some heavy rain onshore over portions of the Carolinas/southern Mid-Atlantic. Tropical moisture overrunning the aforementioned front could spread lighter rain farther north across the Eastern Seaboard, with Cape Cod, Martha's Vineyard, and Nantucket having the best chance of rain with their eastern geographical position. Another area to watch for potentially heavy rain is the western/central Gulf Coast. A tropical area of low pressure is expected to meander in the Bay of Campeche/western Gulf of Mexico over the next several days causing heavy rain over water. At this time, it remains questionable if much of this rainfall will make its way onto the Texas and Louisiana coastlines, so no heavy rain hazard area was drawn there for now. The upper-level flow in the medium range is forecast to start out fairly amplified, 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. Below normal temperatures are forecast all the way south to the Southeast. Farther west, an upper-level ridge of high pressure is expected over the Four Corners to Northern Rockies Friday, with its axis shifting to the Plains over the weekend as an upper-level low pushes eastward across the Northwest. Above normal temperatures are forecast under the ridging before a cooldown with the upper low, which could also cause modest rainfall, particularly over the Northern Rockies. Meanwhile, fire danger is a possibility south of the jet stream over the Great Basin. Alaska can expect a busy period weather-wise. A first round of low pressure systems traversing the area is expected late this week, which could cause locally heavy precipitation along the Gulf of Alaska coast (with potential for snow at higher elevations) on Friday after a windy and rainy/snowy Thursday in the south-central part of the state (now in the short range period). Some possibly heavy rainfall could occur over much of the Panhandle on Sunday as subtropical moisture is pulled into the frontal system. Then, another large surface low pressure system is forecast to move southeast from the Bering Sea across the Aleutians around Monday into the Gulf of Alaska Tuesday. 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. Another threat with this system will be a round of heavy precipitation from the eastern Aleutians into the Alaska Peninsula toward the Kenai Peninsula for Monday/Tuesday, along with heavy rain potential once again for the Panhandle by Tuesday. Tate