US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 240 PM EST Thu Feb 27 2020 Valid Sunday March 01 2020 - Thursday March 05 2020 Hazards: - Heavy rain across portions of the Southern Plains, the Lower/Middle Mississippi Valley, the Tennessee Valley, the Ohio Valley, the Great Lakes, the Southern/Central Appalachians, the Southeast, and the Mid-Atlantic, Mon-Wed, Mar 2-Mar 4. - Heavy snow across portions of the Pacific Northwest, the Northern Rockies, and the Northern Great Basin, Mon-Tue, Mar 2-Mar 3. - Heavy snow across portions of the Central/Northern Rockies and the Central/Northern Great Basin, Tue, Mar 3. - Heavy snow across portions of the Southern/Central Rockies, the Central Great Basin, and the Central Plains, Sun, Mar 1. - Severe weather across portions of the Southeast, the Lower Mississippi Valley, the Southern Plains, and the Tennessee Valley, Tue, Mar 3. - Flooding occurring or imminent across portions of the Central Plains, the Lower/Middle Mississippi Valley, the Tennessee Valley, the Southeast, the Southern Plains, and the Ohio Valley. - Flooding likely across portions of the Southeast. - Much below normal temperatures across portions of the Southeast, Sun, Mar 1. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Sun-Mon, Mar 1-Mar 2. - High winds across portions of mainland Alaska and the Aleutians, Sun, Mar 1. - Much below normal temperatures across portions of mainland Alaska, Sun-Thu, Mar 1-Mar 5. - Much below normal temperatures across portions of mainland Alaska, Tue-Thu, Mar 3-Mar 5. Detailed Summary: The medium range period will begin on Sunday with an upper-level trough dropping southward along the U.S. West Coast, with slight ridging over the central U.S. and northwest flow across the Eastern Seaboard. This upper trough will be the main player causing potentially hazardous weather throughout the period as it moves south and then turns eastward. First, some gusty winds and higher than normal wave heights are possible early in the week along the West Coast, but do not appear to rise to the level of delineating hazard areas. Some light to modest precipitation is expected for the western U.S., but is not forecast to be particularly heavy. One exception could be upslope flow leading to heavy snow across portions of the Central Rockies Sunday. As the trough pivots through the Southwest into the Plains, Pacific Ocean moisture at middle to upper levels and Gulf of Mexico moisture at low levels will combine to cause the potential for widespread heavy rainfall beginning Monday. Currently, the best chance for multiple inches of rain is through Arkansas and parts of the Tennessee and Ohio Valleys. Uncertainty remains regarding the axis of the heaviest precipitation as well as the extent. Some model guidance takes heavy precipitation more to the west and some takes it farther south (which would cause further issues in the Southeast given how wet they have been over the past month or so), so the details have yet to be resolved. The magnitude of the rainfall amounts should decrease by Thursday as the trough moves more progressively farther east, but more rain is possible somewhere along the Eastern Seaboard Thursday. Onshore flow from the Pacific should increase into the Northwest early in the workweek. Differences in the models regarding the forcing remain, but it seems higher elevations of the Cascades and the Northern Rockies could see some heavy snow beginning Monday and continuing into Tuesday. Heavy snow is possible for the Wind River Range/Tetons by Tuesday, but snow chances should decrease in the West by midweek. Temperature-wise, the initial northwest flow over the East could create temperatures a few degrees below normal, with the Florida peninsula having one more day of anomalously cold temperatures on Sunday. Warmer than average temperatures are likely under the ridging ahead of the main trough across the central to eastern U.S. The warmth extending so far northward should keep most of the heavy precipitation in the East as rain, but some light wintry precipitation is possible on the northern edge of the precipitation shield in the Great Lakes and the interior Northeast. A deep surface low pressure system is forecast to track north of the Aleutians into the Bering Sea this weekend, which should cause high winds continuing over the Aleutians on Sunday. Additionally, precipitation should spread across the Aleutians into the southwestern mainland over the weekend, then along the south-central Gulf of Alaska coast and into the Panhandle as a long fetch of moisture streams into those areas. Model guidance did not give particularly high precipitation totals except over the Panhandle, so limited the Heavy Precipitation area to that area. General upper-level troughing should cause below normal temperatures over much of the mainland through the period, spreading southward midweek. Heavy rainfall is possible over Hawaii this weekend into early next week. An upper-level low over the islands will provide forcing, and ample moisture could be drawn into this low to lead to the potential for heavy rain, especially over the Big Island. The upper low is expected to erode by midweek, decreasing the heavy rain threat. Tate