US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 318 PM EDT Fri Aug 14 2020 Valid Monday August 17 2020 - Friday August 21 2020 Hazards: - Heavy rain across portions of the Southeast, the Mid-Atlantic, and the Southern Appalachians, Tue-Wed, Aug 18-Aug 19. - Heavy rain across portions of the Southeast, Thu-Fri, Aug 20-Aug 21. - Flooding possible across portions of the Upper Mississippi Valley and the Northern Plains. - Excessive heat across portions of the Pacific Northwest, the Northern Rockies, the Northern Great Basin, and the Northern Plains, Mon-Tue, Aug 17-Aug 18. - Excessive heat across portions of California, the Central Great Basin, the Pacific Northwest, the Northern Rockies, and the Northern Great Basin, Mon-Wed, Aug 17-Aug 19. - Excessive heat across portions of the Central Great Basin, California, and the Southwest, Mon-Thu, Aug 17-Aug 20. - Much above normal temperatures across portions of the Central Rockies and the Central Great Basin, Mon-Thu, Aug 17-Aug 20. Detailed Summary: The dominant weather hazard during the medium range period (Mon, Aug. 17 - Fri, Aug. 21) is the ongoing heat wave across the western third of the CONUS. Excessively hot conditions look to persist across the Southwest and into the San Joaquin and Sacramento Valleys much of, if not all, of next week. The interior Northwest should be excessively hot temperatures the first half of the week before less intense, albeit still abnormally warm, temperatures the latter half of the period. Portions of the Great Basin and Intermountain West can also expect sizzling temperatures through mid-week. Temperatures may become a tad cooler as monsoonal flow returns to parts of the southern and central Rockies. That said, the presence of the upper ridge will keep abnormally hot conditions in the forecast. Due to the ongoing severe drought conditions and lack of rich moisture aloft, dry thunderstorms are likely to transpire across the Southwest and Rockies, which combined with a potentially breezier wind pattern aloft could lead to increased fire weather potential across these regions. Precipitation-wise, the presence of an upper trough over the east-central U.S. favors wetter than normal conditions over the Southeast mid-late week. The trough may become cut-off from the mean flow over southeast Canada and a stationary front is forecast to set up from the Carolinas to the Gulf Coast. This boundary should become the focal point for precipitation with rainfall rates that could become excessive in localized areas. If a more organized wave of low pressure develop along the Gulf Coast the second half of next week, then there could be a more pronounced area for heavy rainfall in the Southeast or along the Gulf Coast late next week. Where the heaviest rainfall amounts sets up more than likely come down to mesoscale features which this far out is difficult to nail down. We will also be monitoring a cold front swinging through the Upper Mississippi Valley that could lead to rounds of heavy showers and thunderstorms, but there remains uncertainty in both precipitation totals and areas most affected. In Alaska, a series of low pressure systems look to swing through the Gulf of Alaska both to start the period and into late next week. Model guidance does indicate perhaps some of the highest elevations of the Panhandle could receive rainfall amounts that could approach heavy rainfall criteria, but this Monday will be on the back-end of the heaviest rainfall occurring on Sunday, and ensemble guidance still shows considerable spread in rainfall totals in days 5-7. Still, the pattern stays quite wet in an area where the summer has been quite wet. Rivers and streams will likely be monitored not just this week but in the weeks to come thanks to the much above normal rainfall amounts this season. Temperatures are expected to be warmer than average across western regions and interior Alaska through early next week, with highs in the 70s and even nearing 80 degrees. Far northern Alaska may begin to cool to more seasonal levels the second half of the week. Mullinax