Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 349 PM EDT Fri Jul 21 2017 Valid 00Z Sat Jul 22 2017 - 00Z Mon Jul 24 2017 ...The hot and humid conditions plaguing the eastern U.S. from the central Plains to the Mid-Atlantic region will continue into the weekend... ...Heavy rain and severe weather will be possible in the Upper Midwest, Great Lakes, and Ohio Valley and will shift to the northern Mid-Atlantic region by the weekend... ...Monsoonal moisture moving into the Southwest in addition to the central and southern Rockies will bring a threat of localized flash flooding... The upper level ridge that spans from the central Plains to the Mid-Atlantic states will continue to maintain the hot and humid conditions across these regions through Friday and Saturday. Many states in the Plains, Middle Mississippi Valley, and even the Southeast have excessive heat warnings and heat advisories; high temperatures are expected to reach near or at the century mark and heat indices climbing to 110 degrees or higher. The Mid-Atlantic region and a large portion of North Carolina also have heat advisories in addition to a small area of excessive heat warnings. On Saturday, a cold front will push southward across the Plains and Mississippi Valley and will bring relief from the heat by Sunday across these areas. High temperatures are expected to cool down and be closer to seasonal average. However, hot and humid conditions will still continue for the Mid-Atlantic and the Carolinas on Sunday as the front will not move through these areas until early next week. A wavy frontal boundary that will stretch from the Upper Midwest and Great Lakes to the Ohio Valley and Mid-Atlantic region will be the dominant feature that help focus showers and thunderstorms along it through the weekend. With plenty of instability and moisture present, convection leading to flash flooding and severe weather will be possible in these regions. Tonight and into early Saturday morning, most of the convection is expected to occur in the Upper Midwest/Upper Great Lakes. Throughout most of Saturday, showers and thunderstorms will move along the boundary across the Ohio Valley and lower Great Lakes. By Saturday night and into Sunday, the focus of heavy rain and severe weather shifts to the northern Mid-Atlantic. See WPC's excessive rainfall outlook and SPC's convective outlook for specific information on flash flooding and severe weather, respectively. Monsoonal moisture combining with weak energy aloft will fire off showers and thunderstorms across the Southwest and the central/southern Rockies on Friday through Sunday. Most of this activity can be expected in the late afternoon and early evening as daytime heating will help trigger the convection. Some of these thunderstorms could produce heavy downpours and lead to localized flash flooding. Daytime heating will also lead to afternoon showers and thunderstorms across the Gulf Coast states. Meanwhile, a front approaching British Columbia bought bring light precipitation to northwestern Washington on Saturday. Reinhart Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php