US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 414 PM EDT Thu Jul 16 2020 Valid Sunday July 19 2020 - Thursday July 23 2020 Hazards: - Heavy rain across portions of the Northern/Central Plains and the Upper/Middle Mississippi Valley, Sun-Mon, Jul 19-Jul 20. - Flooding occurring or imminent across portions of the Upper Mississippi Valley and the Northern Plains. - Flooding likely across portions of the Middle Mississippi Valley. - Excessive heat across portions of the Central Plains, the Upper/Middle Mississippi Valley, the Great Lakes, the Ohio Valley, and the Central Appalachians, Sun, Jul 19. - Excessive heat across portions of the Middle/Lower Mississippi Valley, the Ohio Valley, the Tennessee Valley, and the Southeast, Sun-Mon, Jul 19-Jul 20. - 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 Central Appalachians, the Ohio Valley, the Mid-Atlantic, and the Northeast, Sun, Jul 19. - Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Sun-Mon, Jul 19-Jul 20. Detailed Summary: The medium range period (Sunday, July 19 - Thursday, July 23) will continue to feature a summer-like pattern with 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 Mississippi Valley, the Tennessee/Ohio Valleys, and Southeast early in the week. 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 Sunday, but heat indices over 105 could remain across the Lower Mississippi and Tennessee Valleys through Monday, but these high heat indices look to become more isolated later in the week. 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 or just a few degrees above normal for this time of year. The main consistent spot where temperatures could be below normal is the Northern Plains on the cool side of a front. 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 early next week is a frontal boundary forecast to stall over the Middle Mississippi Valley and Central Plains. Heavy rain could occur as copious amounts of moisture flow into this boundary. The exact placement of the heavy rainfall amounts will change depending on the positioning of the front. 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. Southwestern Florida could see heavy rainfall around Tuesday, but heavy amounts may remain offshore. Another area to watch for heavy rain potential is eastern North Carolina from midweek onward, but model guidance continues to vary. Over Alaska, moisture streaming ahead of a low pressure system tracking across the southern coast could lead to heavy rainfall for the Panhandle early next week. Showers are also likely over interior Alaska through the period, but organized heavy rainfall is not expected there. Some rain may also spread into the Aleutians around midweek as another low pressure system moves across. A cold upper-level trough will lead to cooler than normal conditions across much of the state, but especially over the North Slope, where high temperatures could be as much as 30 degrees below average through Tuesday, and low temperatures could be below freezing. Tate