Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 306 PM EDT Sat Aug 13 2016 Valid 00Z Sun Aug 14 2016 - 00Z Tue Aug 16 2016 ...Flash flooding possible from the southern plains and lower Mississippi valley to the Northeast... ...Dangerous heat expected to continue through Sunday across portions of the Mid-Atlantic and Northeast... An area of low pressure of tropical origin continues to drift slowly west across the lower Mississippi valley this afternoon. The system continues to produce very heavy rainfall, and has resulted in catastrophic flash flooding across Louisiana. This area of low pressure is forecast to continue moving generally westward tonight as it merges with a stationary frontal boundary. As the tropical moisture associated with this area of low pressure interacts with and spreads out along the stationary frontal boundary, the threat of heavy rainfall will expand along the front, with at least a slight risk of flash flooding tonight over a large area from the southern plains to the mid-Mississippi/Ohio valleys and even the Northeast. Showers and thunderstorms with very heavy rain will continue into Sunday and even Monday from the southern plains to the mid-Mississippi and Ohio valleys as the frontal boundary moves very little and the area of low pressure drifts northeastward along the front. A ridge of high pressure aloft will persist along the Eastern Seaboard through Monday, keeping conditions hot and humid. Afternoon high temperatures will once again be 5 to 15 degrees above average on Sunday across much of the Mid-Atlantic and Northeast, with temperatures only cooling by a couple degrees on Monday. These hot temperatures will combine with extremely high humidity to produce dangerous heat indices which may near or surpass 110 degrees in some areas. Heat advisories and excessive heat warnings remain in effect from the Mid-Atlantic to southern New England. Farther west, high pressure will keep conditions mostly dry with above average temperatures across the western U.S. A few isolated showers and thunderstorms will be possible each afternoon across the higher terrain of the Rockies. By Monday afternoon, an upper-level disturbance will move into the northern plains from the Canadian Rockies, resulting in scattered showers and thunderstorms. Ryan Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php