US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 252 PM EST Wed Feb 26 2020 Valid Saturday February 29 2020 - Wednesday March 04 2020 Hazards: - Heavy precipitation across portions of the Pacific Northwest, Mon-Tue, Mar 2-Mar 3. - Heavy rain across portions of the Central/Southern Plains, the Middle/Lower Mississippi Valley, the Tennessee Valley, the Ohio Valley, the Great Lakes, the Central/Southern Appalachians, the Mid-Atlantic, and the Northeast, Mon-Wed, Mar 2-Mar 4. - Heavy snow across portions of the Pacific Northwest, the Northern Rockies, and the Northern Great Basin, Mon-Wed, Mar 2-Mar 4. - Heavy snow across portions of the Central/Northern Rockies, the Central/Northern Great Basin, and the Northern Plains, Tue-Wed, Mar 3-Mar 4. - Heavy snow across portions of the Southern Rockies, the Central Rockies, and the Central Great Basin, Sun-Wed, Mar 1-Mar 4. - Flooding occurring or imminent across portions of the Central Plains, the Lower Mississippi Valley, the Tennessee Valley, the Middle Mississippi 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 Great Lakes, the Ohio Valley, and the Upper Mississippi Valley, Sat, Feb 29. - Much below normal temperatures across portions of the Southeast, Sat-Sun, Feb 29-Mar 1. - High winds across portions of mainland Alaska and the Aleutians, Sat-Sun, Feb 29-Mar 1. - Much below normal temperatures across portions of mainland Alaska, Sat, Feb 29 and Tue-Wed, Mar 3-Mar 4. - Much below normal temperatures across portions of mainland Alaska, Sat-Wed, Feb 29-Mar 4. - High significant wave heights for coastal portions of the Aleutians, Sat-Sun, Feb 29-Mar 1. Detailed Summary: The upper-level pattern in the medium range will begin with troughing over the eastern U.S. Saturday, which will lead to colder than normal temperatures underneath it. The coldest air is expected over the Midwest to Great Lakes region into the Ohio Valley. Additionally, the Florida peninsula will remain cooler than average by 10 degrees or so through the weekend with those below normal heights. Upstream, an upper-level ridge across the western to central U.S. Saturday is forecast to redevelop over the eastern U.S. by midweek. Thus, above average temperatures are likely across the western to central U.S. over the weekend, shifting into the Mississippi, Ohio, and Tennessee Valleys early next week and toward the Eastern Seaboard midweek. Another upper-level trough is forecast to move southward along the West Coast Saturday through Monday before turning eastward at the beginning of the workweek. A round of precipitation could spread across the West with this, 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 into Monday. As the trough pivots through the Southwest into the Plains, Gulf of Mexico moisture ahead of it will flow into the Southern/Central Plains eastward and cause the potential for heavy rainfall into the Mississippi, Ohio, and Tennessee Valleys, where flooding could be a threat. This rainfall should spread a bit eastward into the Southern and Central Appalachians on Wednesday. Some light wintry precipitation is possible on the northern edge of the precipitation shield in the Midwest to Great Lakes and the interior Northeast, and this potential threat will continue to be monitored, but the warmth extending so far northward will mean this is mostly a rain event. Onshore flow from the Pacific should increase by Tuesday and Wednesday into the Northwest. Differences in the models regarding the forcing remain, but it seems higher elevations of the Cascades could see some heavy snow and the Pacific Northwest coast can expect heavy precipitation (higher elevation snow and lower elevation rain) by Monday. The Rockies and Wind River Range/Tetons can expect heavy snow as well by Tuesday and Wednesday in particular. 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 and significant waves over the Aleutians. Additionally, precipitation could 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. The precipitation in model guidance seems to stay below thresholds for drawing hazard areas, but will continue to be monitored. Eastern/central portions of mainland Alaska are expected to remain colder than average throughout the period under slightly below normal heights. Western portions of the mainland should start out cold but may warm up for a time early next week before cooling down again. 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. Tate