US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 323 PM EDT Wed May 06 2020 Valid Saturday May 09 2020 - Wednesday May 13 2020 Hazards: - Heavy rain across portions of California and the Pacific Northwest, Mon-Tue, May 11-May 12. - Heavy rain across portions of the Southern Plains, Sat, May 9. - Heavy rain across portions of the Southeast, Sun-Mon, May 10-May 11. - Flooding occurring or imminent across portions of the Middle/Lower Mississippi Valley, the Great Lakes, and the Northern Plains. - Flooding likely across portions of the Northern Plains. - Much above normal temperatures across portions of the Central/Northern Great Basin, the Northern Rockies, California, the Pacific Northwest, and the Southwest, Sat-Sun, May 9-May 10. - Much above normal temperatures across portions of the Central/Northern Great Basin and the Northern Rockies, Sat-Mon, May 9-May 11. - Much below normal temperatures across portions of the Plains, the Mississippi Valley, the Ohio Valley, the Tennessee Valley, the Great Lakes, the Southern/Central Appalachians, the Southeast, and the Mid-Atlantic, Sat-Tue, May 9-May 12. - Much below normal temperatures across portions of the Great Lakes, the Mid-Atlantic, the Northeast, the Central Appalachians, and the Ohio Valley, Sat-Wed, May 9-May 13. - Much above normal temperatures across portions of mainland Alaska, Sat-Wed, May 9-May 13. - Much above normal temperatures across portions of the Alaska Panhandle, Sat-Mon, May 9-May 11. Detailed Summary: The medium range period (Saturday 5/9 to Wednesday 5/13) will be characterized by an upper-level trough across the eastern half of the contiguous U.S., with shortwave troughs progressing through the general troughing pattern. Much below normal temperatures are forecast due to the below normal heights, with multiple rounds of cold air in some areas as cold high pressure systems build in behind cold fronts. Temperatures will be closer to March values than May, below freezing temperatures are forecast for parts of the Midwest to Ohio Valley and Northeast on Saturday, and dozens of record low minimum and maximum temperatures will be set over the weekend. The cold air is expected to persist across the Great Lakes region to portions of the Ohio Valley and Mid-Atlantic Northeast through midweek, but farther south and west temperatures should moderate to about normal after Tuesday. With the cold temperatures, there is even the possibility for a few inches of snow in the Central Appalachians to interior Northeast behind a low pressure system forecast to be near the coast of Maine on Saturday morning. Heavy snow should be limited to localized areas, but would certainly be unusual for May. Meanwhile over the West, an upper-level ridge should shift from the West Coast Saturday eastward into the Great Basin for the beginning of next week. Above normal temperatures are expected underneath the ridge, and a handful of record highs and high minimum temperatures could be set. Heat could be close to excessive across the Southwest once again, particularly Saturday. Then an upper-level low is forecast to approach the West on Monday and Tuesday, cooling down temperatures and leading to precipitation in the Pacific Northwest and northern California. Heavy rain is possible, with the best chance currently across northwestern California and southwestern Oregon. But some rain is forecast all across the Pacific Northwest toward the Cascades, then spreading into the Northern Great Basin and Northern Rockies by Tuesday and Wednesday. Most precipitation should fall as rain, but the highest elevations could see a couple of inches of snow. Given the strong trough in the eastern half of the contiguous U.S., a cold front will be pushed far south into southern Texas, across the Gulf, and into Florida, leading to heavy rain in those areas. Southern Texas can expect locally heavy rain for the end of the week, and the front stalling over the Florida peninsula on Sunday and Monday will create heavy rain potential there, likely lingering over the Keys on Tuesday, and with some potential for moisture return over coastal parts of southern Florida by midweek. The rain should keep temperatures there a few degrees below normal, and on Sunday record low maximum temperatures could be set in the peninsula. Elsewhere, a frontal system moving through the Northern Plains to Midwest could cause some moderate rain over the weekend there, with gusty to potentially strong winds behind the cold front across the Northern/Central Plains on Saturday. Then, rain chances increase over portions of the Central/Southern Plains and Middle/Lower Mississippi Valley by Monday and Tuesday, but uncertainty remains regarding the axis of heaviest precipitation and if amounts will be truly heavy. Over Alaska, above normal temperatures can be expected over the mainland with a persistent upper-level ridge overhead. A strong low pressure system in the Bering Sea could bring rain and gusty winds to the Aleutians Saturday, but stay quite a bit west of the mainland. Meanwhile, ice jam and snowmelt flooding remain threats across some areas of the mainland where rivers have not yet opened up, particularly the Middle Yukon River. Tate