Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 400 PM EDT Wed Jun 20 2018 Valid 00Z Thu Jun 21 2018 - 00Z Sat Jun 23 2018 ...Additional flash flooding expected for portions of the Texas coast before improving conditions by the end of the week... ...A threat for flash flooding will continue from the Midwest to the Mid-Atlantic through the end of the week... ...Increasing temperatures expected through the end of the week from California into the Southwest and Texas... A slow moving front stretching from the Mid-Atlantic coast to the southern Plains will continue to pose a threat for thunderstorms and flash flooding over the next couple of days, but with waning coverage across the lower 48 each day. Conditions near and south of the frontal boundary will see high humidity with anomalously high moisture values which will support diurnally driven thunderstorms during the afternoon and evening hours. Some of these thunderstorms will have the ability to produce strong to locally severe weather in addition to heavy downpours with flash flooding. One of two significant threats for flash flooding through Thursday morning exists in the vicinity of northwestern Iowa into portions of eastern South Dakota/Nebraska near a surface low and out head of an upper level disturbance crossing the Plains. An equally concerning threat is in place from South Texas, up the coastal plain into the Sabine River valley where some locations have received 5 to 15 inches over the past 72 hours. A slow moving upper level low over South Texas will gradually begin to shift south and west over the next 12 to 36 hours, allowing for a reduction in available moisture and lift which should end the flash flood threat with Friday likely a dry day for the region as well as Saturday. Thursday's threat for flash flooding will again be focused in the vicinity of the front, with a focus over Illinois, Indiana into eastern Kentucky, but with reduced coverage for much of the Plains. Widespread coverage of thunderstorms will still be expected near and south of the front however. Out West, ahead of an upper level disturbance approaching through the eastern Pacific, high temperatures are expected to increase across California, the Southwest and Texas with triple digit heat forecast for all three locations on Friday. Excessive heat watches have already been posted for portions of the Sacramento valley into southern Arizona in anticipation of temperatures rising to and above 105 degrees. Otto Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php