US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 458 PM EDT Wed Aug 04 2021 Valid Saturday August 07 2021 - Wednesday August 11 2021 Hazards: - Heavy rain across portions of the Midwest, Sat-Sun, Aug 7-Aug 8. - Heavy rain across portions of the Southwest, Sat-Mon, Aug 7-Aug 9. - Flooding possible across portions of the Southeast. - Excessive heat across portions of the Central/Southern Plains and the Middle and Lower Missouri and Mississippi Valleys, Sun-Tue, Aug 8-Aug 10. - Excessive heat across portions of the Southern Plains and Lower Mississippi Valley, Sun-Wed, Aug 8-Aug 11. - Heavy rain across portions of the Alaska Panhandle and Southcentral mainland Alaska, Sun-Tue, Aug 8-Aug 10. Detailed Summary: The potential for heavy rain in the Midwest and hot weather in the central part of the country highlight the hazards outlook for the medium range forecast period (Saturday, August 7 - Wednesday, August 11). A shortwave trough will move east across the Northern Plains and Midwest Saturday (August 7) and Sunday (August 8). At the surface, a series of warm fronts will move north across the region, advecting higher moisture northward and further encouraging shower and thunderstorm development. Widespread heavy rain totals of 1 to 2 inches, with locally higher amounts, look likely from Iowa and central/southern Minnesota east across Wisconsin, northern Illinois, and western portions of Michigan. The rain chances are highest further west on Saturday and shift to the east on Sunday. As this trough departs to the east, heat will return to the Central/Southern Plains as well as the mid- and lower Missouri and Mississippi Valleys beginning on Sunday and last through the end of the period. High temperatures in the mid- to upper 90s combined with dewpoints in the 70s will lead to afternoon heat indices of 105 and higher. Additionally, there will be little relief overnight as temperatures only fall into the mid- to upper 70s. A cold front approaching the region from the north as well as another trough moving across the Northern Tier from the west look to bring cooler temperatures to the northern portion of the outlook area by Wednesday (August 11). In the southwest, heavy rain is also a concern for southeastern Arizona from Saturday through Monday (August 9) as moisture increases from the south, encouraging the chance for Monsoonal showers. Daily rainfall amounts greater than 0.5 inches appear probable. These showers may continue later into the period and spread further north into Arizona, but there is less consistency across the model guidance for heavier rainfall amounts as the surface moisture does not look to be as high. Elsewhere, showers and storms look likely to form across the eastern Carolinas along a dying stationary boundary on Saturday. However, rainfall amounts do not look to be particularly hazardous at this time. Additionally, an upper-level ridge will build to the north over the East Coast towards the end of the period. The combination of high temperatures above 90 as well as increasing humidity may lead to afternoon heat indices approaching 100 degrees and overnight lows in the 70s, particularly for southern portions of the Mid-Atlantic. This heat looks to continue beyond the current medium-range forecast period as well. For now, the heat does not look hazardous enough for an outlook area. However, the region will be monitored for a potential outlook area in the future if confidence increases in the potential for more widespread, oppressive, and long-lasting heat. In Alaska, the chance for significant rainfall of several inches over multiple days has been increasing for southern portions of the mainland and into the Panhandle. A storm system over the Bering Sea will move east across the southern mainland as well as the Gulf of Alaska Sunday morning. Increasing moisture ahead of a warm front moving north towards the coastal Kenai Peninsula, Southcentral, and the northwestern Panhandle will lead to daily showers from Sunday through Tuesday. Rainfall totals over 2 inches are likely with significantly higher amounts possible. Additional showers look likely further south into the Panhandle and may continue later into the period, but the current outlook area was chosen to highlight the region where model guidance is most consistent on the location of significant heavy rainfall. The Alaskan Peninsula may also see some heavy rain as well as high winds Sunday into Monday as the system moves through. However, the rainfall amounts and winds do not appear to be particularly hazardous at this time. Putnam