Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 347 PM EDT Tue Jun 19 2018 Valid 00Z Wed Jun 20 2018 - 00Z Fri Jun 22 2018 ...Flash flooding and strong thunderstorms expected from the Central Plains eastward across the Ohio Valley and into the Mid-Atlantic region... ...Heavy showers and flash flooding continues along and near the Texas coast... ...Hot weather continues across the Carolinas...and gradually builds again over the Southwestern U.S... A slow-moving frontal system extending from the Central Plains eastward across the Middle Mississippi Valley, Ohio Valley, and Mid-Atlantic states will remain a focus for multiple rounds of showers and thunderstorms through Thursday. With a very warm and humid air mass aligned with the front, some of the storms could be severe, as well as produce localized excessive rainfall and flash flooding. During Tuesday night and Wednesday, an upper level disturbance moving out of the Rockies will help bring the best chance of widespread rainfall to the Plains and Middle Mississippi Valley. As this disturbance pushes eastward on Thursday, the high Plains will begin to dry out, but widespread showers/thunderstorms will continue over the Mississippi Valley and extend eastward along the front through the Ohio Valley and central Appalachians. South of this front, deep tropical moisture and a trough of low pressure extending from a low in southern Texas will continue the threat for widespread heavy rainfall across eastern and southeastern Texas through Wednesday. Flash flood watches are posted across this region given the high moisture values in place and heavy rains that fell on Monday. During Thursday, the most organized activity of showers and thunderstorms will tend to be drawn north and eastward into the lower Mississippi Valley ahead of a slow-moving cold front, though a weak upper level disturbance will maintain the threat heavy, slow-moving storms and localized flooding across eastern Texas. Farther east over the Carolinas, the heat wave will continue, with highs ranging into the mid-upper 90s through Thursday. As a result, heat advisories remain in effect for eastern sections of North and South Carolina. Hot weather will begin to abate over southern Virginia and sections of the middle Mississippi Valley as clouds and the chance for rain increases in association with the aforementioned slow-moving frontal boundary. Across the western U.S., dry and very warm conditions will persist through Wednesday over the Pacific Northwest; however, an upper level trough moving in from the Pacific will bring clouds and cooler conditions by Thursday. Over the Southwest, a building upper ridge will bring increasingly hot conditions to the region through the end of the week. Excessive heat warnings are posted from sections of southeastern California, southern Nevada and southern Arizona. Over the northern tier of states, persistent clouds and showers over the northern Intermountain region/Rockies and high Plains will briefly abate on Wednesday as high pressure builds in. By Thursday, however, the upper trough that brings cooler temperatures to the Pacific Northwest will move inland and potentially trigger another round of rainfall for the region. Mostly dry conditions are expected from the upper Mississippi Valley eastward across the Northeast. A weakening cold front may bring scattered showers or thundershowers to New England Wednesday afternoon, but rainfall amounts should be light. Klein Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php