US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 335 PM EDT Tue Aug 11 2020 Valid Friday August 14 2020 - Tuesday August 18 2020 Hazards: - Heavy rain across portions of the Upper Mississippi Valley, Fri, Aug 14. - Heavy rain across portions of the Southeast, the Southern/Central Appalachians, and the Mid-Atlantic, Fri-Sun, Aug 14-Aug 16. - Flooding occurring or imminent across portions of the Middle Mississippi Valley. - Excessive heat across portions of the Central Great Basin, California, and the Southwest, Fri-Tue, Aug 14-Aug 18. - Excessive heat across portions of California, Sat-Sun, Aug 15-Aug 16. - Excessive heat across portions of the Southern Plains, Fri, Aug 14. - Excessive heat across portions of the Lower Mississippi Valley and the Southern Plains, Fri-Sun, Aug 14-Aug 16. - Much above normal temperatures across portions of California, the Pacific Northwest, the Great Basin, and the Northern Rockies, Sat-Mon, Aug 15-Aug 17. - Much above normal temperatures across portions of the Southern Plains, Fri, Aug 14. - Heavy rain across portions of the Alaska Panhandle, Sat-Mon, Aug 15-Aug 17. Detailed Summary: The medium range period (Friday, Aug. 14 to Tuesday, Aug. 18) 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, first across the Upper Mississippi Valley on Friday, where heavy rain could continue from the short range period. The southeastern to east-central U.S. can also expect scattered to widespread rain and storms, particularly during afternoon and evening hours as daytime heating increases the thunderstorm potential. Currently, it appears the best chance for focused heavy rainfall will be across the Southern and Central Appalachians eastward into the Carolinas and Mid-Atlantic through the weekend. The Northeast may see some rain on Monday/Tuesday as a front moves across, but amounts and placement of the heaviest rain are uncertain there, and the front is likely to be progressive, so a heavy rain hazard area was not delineated there. Meanwhile, an upper-level high is forecast to retrograde across the Southwest and build ridging across the West over the weekend into early next week. Excessive heat will be most 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. Late this week will be hot for the Southern Plains to Lower Mississippi Valley. Temperatures of over 100 degrees are forecast for the Southern High Plains, but lower humidity will hold heat indices down. Farther east, higher heat indices are more likely with higher dewpoints across eastern portions of the Southern Plains into the Lower Mississippi Valley. While warm to hot weather is forecast all across the West under the ridge, with temperatures several degrees above average, highs are expected to be most anomalous starting in the Pacific Northwest on Saturday and spreading to the Northern Great Basin early next week. Additionally, excessive heat is a concern for the California valleys this weekend. Record high temperatures are possible for the West to Southern Plains. In Alaska, a low pressure system is forecast to move across the Gulf of Alaska and approach the Panhandle this weekend. Moisture inflow with this cyclone could lead to heavy rain in the southeastern part of the Panhandle Saturday, and heavy rain chances increase for the rest of the Panhandle on Sunday into Monday. Another low pressure system is currently forecast to track near the Aleutians early next week, while another front drops southward across the western part of the state. There is some potential for heavy rain and wind 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 through early next week, with highs in the 70s. Tate