US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 251 PM EDT Thu May 07 2020 Valid Sunday May 10 2020 - Thursday May 14 2020 Hazards: - Heavy rain across portions of California and the Pacific Northwest, Mon-Tue, May 11-May 12. - Heavy rain across portions of the Central/Southern Plains, the Mississippi Valley, the Great Lakes, and the Ohio Valley, Mon-Thu, May 11-May 14. - Heavy rain across portions of the Southeast, Sun-Wed, May 10-May 13. - Heavy rain across portions of the Southeast, Sun, May 10. - 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 California, the Central/Northern Great Basin, the Pacific Northwest, and the Southwest, Sun, May 10. - Much above normal temperatures across portions of the Central Great Basin, the Northern Rockies, and the Northern Great Basin, Sun-Mon, May 10-May 11. - Much below normal temperatures across portions of the Plains, the Mississippi Valley, the Tennessee Valley, the Ohio Valley, the Great Lakes, the Central/Southern Appalachians,the Mid-Atlantic, and the Southeast, Sun-Tue, May 10-May 12. - Much below normal temperatures across portions of the Northeast, the Central Appalachians, the Mid-Atlantic, the Upper Mississippi Valley, the Great Lakes, and the Ohio Valley, Sun-Wed, May 10-May 13. - Much above normal temperatures across portions of mainland Alaska, Sun-Thu, May 10-May 14. - Much above normal temperatures across portions of mainland Alaska, Sun-Tue, May 10-May 12. Detailed Summary: The medium range period will begin on Sunday 5/10 with much below normal upper-level heights across the central and eastern parts of the U.S., as a potent upper trough settles overhead with shortwave troughs progressing through. This will lead to continued below normal temperatures on Sunday, with many record lows forecast from the Lower Mississippi Valley to the Northeast. Late frosts and freezes are expected in some areas. The general troughing pattern is expected to persist across the Midwest/Great Lakes to Mid-Atlantic/Northeast through midweek, keeping temperatures cold there, but should relax farther south and west, bringing temperatures to about normal in the Plains and Gulf Coast states after Tuesday. Meanwhile over the West, an upper-level ridge over the Great Basin on Sunday should shift slowly eastward and relax during the workweek. A couple days of much above normal temperatures are forecast underneath the ridge, and a handful of record highs and high minimum temperatures could be set. 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 precipitation is forecast all across the Pacific Northwest toward the Cascades and Sierra Nevada, 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 few inches of snow. Given the deep trough in the eastern half of the contiguous U.S., a cold front will be pushed far south across the Gulf and southern Florida, leading to heavy rain there as the front stalls. Sunday is expected to be the wettest day for much of the Florida peninsula, which will also keep temperatures below normal, and record low maximum temperatures could be set. The front should linger near the Keys on Monday, and another front approaching by midweek should create additional chances for rounds of locally heavy rain for southern Florida. Another area where heavy rain is possible is from the Central/Southern Plains toward the Mississippi Valley, as moisture interacts with a stationary front to the south which eventually becomes a warm front. Deterministic model guidance is not in very good agreement with the placement and amounts of the potential rain, so confidence is low, but tried to stay close to the position of the GEFS and ECENS means to outline the Heavy Rain hazard area. Rain and thunderstorms are currently expected to spread northeastward from the Plains Monday to the Middle Mississippi Valley through the week. Over Alaska, above normal temperatures can be expected over the mainland with a persistent upper-level ridge overhead. Temperatures should moderate across the Brooks Range and North Slope by midweek. 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