US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 307 PM EDT Thu Aug 05 2021 Valid Sunday August 08 2021 - Thursday August 12 2021 Hazards: - Heavy rain across portions of the Middle Mississippi Valley, the Great Lakes, and the Upper Mississippi Valley, Sun-Mon, Aug 8-Aug 9. - Heavy rain across portions of the Southwest, Sun, Aug 8 and Thu, Aug12. - Flooding possible across portions of the Southeast. - Flooding likely across portions of the Southeast. - Excessive heat across portions of the Pacific Northwest and the Northern Great Basin, Wed-Thu, Aug 11-Aug 12. - Excessive heat across portions of the Central Plains, the Middle Mississippi Valley, the Lower Mississippi Valley, the Southern Plains, and the Ohio Valley, Sun-Tue, Aug 8-Aug 10. - Excessive heat across portions of the Lower Mississippi Valley, the Tennessee Valley, the Middle Mississippi Valley, the Southeast, the Southern Plains, and the Ohio Valley, Sun-Wed, Aug 8-Aug 11. - Excessive heat across portions of the Mid-Atlantic and the Northeast, Tue-Thu, Aug 10-Aug 12. - Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Sun-Thu, Aug 8-Aug 12. - Heavy rain across portions of the Alaska Panhandle, Mon-Wed, Aug 9-Aug 11. Detailed Summary: The potential for heavy rain in the Midwest and hot weather throughout sections of the country highlight the hazards outlook for the medium range forecast period (Sunday, August 8 - Thursday, August 12). A potent shortwave trough will move east across the Upper Midwest on 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 eastern Iowa across Wisconsin and northern Illinois. 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 lasting through at least Tuesday. High temperatures in the mid- to upper 90s combined with dewpoints in the 70s will lead to afternoon heat indices around 105 degrees 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 slightly cooler temperatures to the the outlook area by midweek. Heat and oppressive humidity will remain across the Gulf Coast regions and Lower Mississippi Valley, but temperatures are forecast to reach near normal for this time of year. In the southwest, heavy rain is also a concern for far southeastern Arizona on Sunday and again by Thursday as moisture periodically increases from the south, encouraging the chance for Monsoonal showers. Daily rainfall amounts greater than 0.5 inches appear probable. Elsewhere, an upper-level ridge will build to the north over the East Coast by Tuesday and could lead to dangerously hot temperatures. The combination of high temperatures above 90 as well as increasing humidity may lead to afternoon heat indices approaching 105 degrees and overnight lows in the 70s, particularly for southern portions of the Mid-Atlantic. Heat will also build along coastal and metropolitan regions in the Northeast as far north as southern Maine, but maximum heat indices here look to stay below 100 degrees as of right now. Excessive heat is also expected to build back into the Pacific Northwest on Wednesday as high temperatures increase to around 10-20 degrees above average. Highs into the mid-to-upper 90s are likely, with triple digits possible throughout interior Oregon and Washington. 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 Thursday as several more waves of rain enter the region. Daily rainfall totals over 2 inches are likely with significantly higher amounts possible throughout the entire period. Additional showers look likely further south into the Panhandle between Monday and the middle of the week., but confidence is much lower for this region. 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. Snell