US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 344 PM EDT Wed Jul 15 2020 Valid Saturday July 18 2020 - Wednesday July 22 2020 Hazards: - Heavy rain across portions of the Central/Northern Plains and the Middle/Upper Mississippi Valley, Sun-Wed, Jul 19-Jul 22. - Heavy rain across portions of the Great Lakes and the Upper Mississippi Valley, Sat, Jul 18. - Flooding possible across portions of the Middle/Upper Mississippi Valley and the Great Lakes. - Flooding occurring or imminent across portions of the Northern Plains. - Flooding likely across portions of the Upper Mississippi Valley. - Excessive heat across portions of the Central/Northern Plains, the Middle/Upper Mississippi Valley, the Great Lakes, the Ohio Valley, and the Southern/Central Appalachians, Sat-Sun, Jul 18-Jul 19. - Excessive heat across portions of the Middle/Lower Mississippi Valley, the Tennessee Valley, the Ohio Valley, and the Southeast, Sat-Tue, Jul 18-Jul 21. - Excessive heat across portions of the Mid-Atlantic, the Northeast, and the Central Appalachians, Sun-Wed, Jul 19-Jul 22. - Much above normal temperatures across portions of the Great Lakes, the Mid-Atlantic, the Northeast, the Central Appalachians, and the Ohio Valley, Sun, Jul 19. - Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Sat-Mon, Jul 18-Jul 20. Detailed Summary: The medium range period (Saturday, July 18 - Wednesday, July 22) will continue to feature a summer-like pattern with expanding heat across the Southwest into the central/eastern U.S. as high pressure persists south of the jet stream located across the northern states. Hot temperatures combined with high dewpoints will lead to high heat indices over much of the Plains, Mississippi Valley, the Tennessee/Ohio Valleys, and Southeast. Warm overnight lows are expected as well, exacerbating the heat threat. The heat in the central U.S. is expected to subside somewhat as a front pushes through over the weekend, but heat indices over 105 could remain across the Lower Mississippi and Tennessee Valleys through Tuesday. Additionally, high heat indices over 100, even approaching 110 in some places, are forecast across the Mid-Atlantic region to the New York City area for the first half of next week, leading to an Excessive Heat area there. Farther north, the Lower Great Lakes and Northeast can expect temperatures several degrees above average, especially Sunday when highs should be in the 90s. The Desert Southwest, southern Texas, and the Florida peninsula should also remain hot, but all those areas are around normal for this time of year. Rain and thunderstorms are possible in the vicinity of fronts moving through north-central and eastern parts of the country through the period. One potential focus for organized convection will be in the Upper Great Lakes region Saturday along a frontal boundary. Then next week, a front is forecast to stall over the Middle Mississippi Valley and Central Plains. As copious amounts of moisture flow into this boundary, heavy rain could occur in those areas. The exact placement of the heavy rainfall amounts will change depending on the positioning of the front, but the ingredients for heavy rainfall are there, so a Heavy Rain hazard area was added to show the potential threat. Rain and thunderstorms are also expected along the Eastern Seaboard, but model guidance is not currently consistent on areas where the rain could focus to become heavy. Over Alaska, the weather looks to be active through the first half of next week. Confidence has increased that moisture streaming ahead of a low pressure system tracking across the southern coast could lead to heavy rainfall for south-central Alaska this weekend and into the Panhandle early next week. Showers are also likely over interior Alaska, but organized heavy rainfall is not expected there. A cold upper-level trough will lead to cooler than normal conditions across much of the state through the period, but especially over the North Slope, where high temperatures could be up to 30 degrees below average. Tate