US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 335 PM EDT Wed Aug 12 2020 Valid Saturday August 15 2020 - Wednesday August 19 2020 Hazards: - Heavy rain across portions of the Southeast, the Southern/Central Appalachians, and the Mid-Atlantic, Sat-Sun, Aug 15-Aug 16. - Excessive heat across portions of the Central Great Basin, California, and the Southwest, Sat-Wed, Aug 15-Aug 19. - Excessive heat across portions of the Lower Mississippi Valley and the Southern Plains, Sat-Sun, Aug 15-Aug 16. - Much above normal temperatures across portions of California, the Pacific Northwest, the Central/Northern Great Basin, and the Northern Rockies, Sat-Mon, Aug 15-Aug 17. - Heavy rain across portions of the Alaska Panhandle, Sat-Sun, Aug 15-Aug 16. Detailed Summary: The medium range period (Saturday, Aug. 15 to Wednesday, Aug. 19) will feature a front moving slowly southward across the eastern U.S., while another front located ahead of an upper-level trough should push through the Midwest, Great Lakes, Mississippi and Ohio Valleys, and Eastern Seaboard through the period. These fronts will provide focuses for rain and thunderstorms. Currently, it appears the best chance for widespread heavy rainfall will be across the Southern and Central Appalachians eastward into the Carolinas and Mid-Atlantic through the weekend. Farther north, rain and thunderstorms (which could be strong to severe) could spread from the Great Lakes region/Upper Ohio Valley Sunday to the Northeast Monday and Tuesday ahead of the front. However, the front is likely to be progressive enough that widespread heavy rainfall is not forecast, but locally heavy rain amounts are possible. The southeastern U.S. can also expect scattered rain and storms, potentially increasing in coverage by Tuesday and Wednesday of next week, and particularly during afternoon and evening hours as daytime heating increases the thunderstorm potential. Meanwhile, an upper-level high is forecast to meander across the Southwest and build ridging across the West over the weekend into early next week. Excessive heat will be persistent in the Desert Southwest, as high temperatures continue to be 110-120 degrees, hotter than average for this time of year as monsoon season has usually taken hold by now. Very hot temperatures are expected to stretch into the lower elevations of California, including the valleys and even approaching the coast in some areas. Excessive Heat Watches are already in effect. While hot weather with temperatures nearing or exceeding 100 degrees are forecast all across the West under the ridge, highs are expected to be most anomalous starting in the Pacific Northwest on Saturday and spreading to the Northern Great Basin early next week. The Northwest should cool down closer to normal around midweek as upper-level troughing coming in presses the high southward. Additionally, heat and high dewpoints will combine to create high heat indices in portions of the Southern Plains to Lower Mississippi Valley this weekend. Record high temperatures are possible for the West to Southern Plains. Meanwhile, temperatures look to be below average for the central U.S. next week. In Alaska, a low pressure system is forecast to spin offshore of Panhandle this weekend. Moisture inflow with this cyclone could lead to heavy rain particularly in the southeastern part of the Panhandle. Another low pressure system is currently forecast to track through the Bering Sea early next week, while another front drops southward across the western part of the state. There is some potential for gusty wind and heavy rain with these features in southwestern Alaska, but currently the large variability in model guidance precludes drawing hazard areas there. Temperatures are expected to be warmer than average for the southwestern part of the state and interior Alaska through early next week, with highs in the 70s and even nearing 80 degrees. Tate