Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 308 AM EDT Sat Jul 22 2017 Valid 12Z Sat Jul 22 2017 - 12Z Mon Jul 24 2017 ...Flash flooding and severe weather will be possible over portions of the Ohio Valley and Mid-Atlantic states this weekend... ...Another day of dangerous heat is expected from the Central Plains and Middle Mississippi Valley to the Mid-Atlantic coast on Saturday... ...Monsoonal moisture will keep localized flash flooding a threat from the Southwest to the Southern and Central Rockies over the next few days... A wavy frontal boundary stretching from the Central Plains to the Mid-Atlantic coast early Saturday will continue to serve as a focus for showers and thunderstorms while it gradually sinks southeastward this weekend. An abundance of moisture and instability along and south of the boundary could lead to heavy downpours and severe weather within developing convection, especially for locations across the Ohio Valley and northern Mid-Atlantic states on Saturday. Strong to severe storms will also be possible farther north over the Upper Mississippi Valley and Great Lakes as amplifying shortwave energy progresses from the Northern Plains to Interior New England this weekend. Hot and humid conditions will persist for locations south of the wavy frontal boundary stretching from the Central Plains to the Mid-Atlantic coast. Widespread excessive heat warnings and heat advisories remain in effect for much of the Central to Southern Plains, Middle to Lower Mississippi Valley, and southern Mid-Atlantic states, where the dangerous combination of high temperatures and dew points will lead to triple digit heat index values on Saturday. Locations across Kansas and Missouri should begin to see relief from the heat as the wavy frontal boundary sinks through the region Saturday night, but elsewhere, the dangerous heat will persist into Sunday. Weak impulses of energy aloft combined with monsoonal moisture should help trigger and fuel scattered convection over the Southwest and Southern to Central Rockies Saturday and Sunday afternoon and evening. Localized flash flooding will be possible given the anomalous moisture in place across the region. Gerhardt Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php