US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 433 PM EDT Tue Jun 29 2021 Valid Friday July 02 2021 - Tuesday July 06 2021 Hazards: - Heavy rain across portions of the Southern Plains, Fri, Jul 2. - Heavy rain across portions of the Northeast, the Mid-Atlantic, the Lower Mississippi Valley, the Central/Southern Appalachians, the Tennessee Valley, and the Southeast, Fri-Sat, Jul 2-Jul 3. - Heavy rain across portions of the the Lower Mississippi Valley and the Southern Plains, Sat-Tue, Jul 3-Jul 6. - Flooding possible across portions of the Central/Southern Plains, the Middle Mississippi Valley, the Ohio Valley, and the Great Lakes. - Flooding occurring or imminent across portions of the Central/Southern Plains, the Middle Mississippi Valley, and the Great Lakes. - Flooding likely across portions of the Middle Mississippi Valley. - Excessive heat across portions of the Pacific Northwest and the Northern Great Basin, Fri-Mon, Jul 2-Jul 5. - Excessive heat across portions of the Northern Plains, Fri-Sat, Jul 2-Jul 3. - Much above normal temperatures across portions of the Pacific Northwest, California, the Northern Great Basin, and the Northern Rockies, Fri-Mon, Jul 2-Jul 5. - Much above normal temperatures across portions of the Northern Rockies, the Northern Plains and the Upper Midwest, Fri-Sun, Jul 2-Jul 4. Detailed Summary: During the medium range period (Friday, July 2nd - Tuesday July, 6th) the highly anomalous ridging that has dominated the upper-level pattern over the western half of the United States will take its last breath as it progressively weakens, but it won't go down without a fight. Daily high temperatures throughout the Northwest will continue to hover 15 to 20 degrees above normal, consistently reaching the upper 90s or low 100s. These anomalously high temperatures will also begin spreading east into the Northern Rockies on Friday before settling into the Northern Plains and Upper Midwest over the weekend. Lucky for these regions the upper-level ridge is expected to quickly deteriorate by Monday, allowing temperatures to quickly fall closer to normal. Due to the ongoing and likely prolonged exposure to oppressively high daytime temperatures in parts of the Columbia Basin, an excessive heat area has been maintained for portions of eastern Washington, northern Oregon, and northwestern Idaho for much of the medium range period. Dangerous heat is also forecast to affect eastern Montana Friday and Saturday, where highs are anticipated to reach triple digits. Though South Dakota may also be exposed to high temperatures early next week, the inclusion of a hazard area was not warranted due to the temperatures being relatively close to average and the excessive heat threshold not being met. Regardless of whether or not an excessive heat hazard area was drawn, in each of these areas residents are urged to take proper precautions to safeguard their health and prevent the onset of heat-related illness. These precautions include: avoiding long periods of time outdoors in the sun, staying hydrated, remaining in a cool or air conditioned location, and canceling outdoor activities during the heat of the day. In stark juxtaposition to conditions out West, the South and East are forecast to experience cooler and wetter weather throughout the course of the medium range due to a deep cut-off low aloft and a slow-moving frontal system extending from the Northeast through the Tennessee Valley to the Central Plains at the surface. Fueled by moisture from the Gulf of Mexico pooling ahead of the system, this frontal boundary will serve as the primary focus for the development of showers and thunderstorms from New England to the Southern Rockies on Friday and Saturday. The slow progression of the system combined with high rainfall rates from convective precipitation could lead to accumulations of 1 to 2 inches in 24 hours in the outlined heavy rain areas. Though most of the affected regions have relatively dry soils and normal streamflow levels, the potential for isolated flooding will be an ongoing concern in areas with more saturated soils that experience multiple rounds or prolonged periods of heavy rainfall. Pushed south by high pressure settling over the Midwest, the frontal system is expected to creep towards and stall over the Gulf Coast for the remainder of the weekend. This stalled positioning will set the stage for a multi-day event along the coast from the Florida Panhandle to southern Texas, where accumulations could reach or exceed 3 to 4 inches over a 3 to 4 day period. Taking into account the highly saturated soils and much above normal streamflow in these areas from recent anomalously high amounts of rain, the risk of widespread flash flooding will be a significant concern. No hazards have been posted for Alaska on today's graphic, however, there are a couple marginal hazards worth noting. The first being relatively high temperatures affecting the eastern Interior on Friday, where daily highs throughout the region will have the potential to reach or exceed 85 degrees. Despite these conditions, a hazard area was not deemed necessary because these anomalously high temperatures will only last one day and are expected to drop closer to normal on Saturday. The second marginal hazard is the potential for heavy rainfall over the weekend on the mainland. Current guidance suggests that rainfall could reach or even slightly exceed the hazardous threshold, however, there is disagreement as to where the heaviest rainfall will occur. Due to the lack of a consensus among the models regarding the location of the highest accumulation totals, it was decided a heavy rainfall area would not be included on today's graphic. Zavadoff