Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 400 PM EDT Tue Aug 15 2017 Valid 00Z Wed Aug 16 2017 - 00Z Fri Aug 18 2017 ...Best chance of strong thunderstorms and heavy rain will be from Nebraska eastward into the upper Midwest through Thursday... An upper-level trough is forecast to slowly develop as another upper-level trough near the Canadian border merges and then interacts with a front across the northern and central Plains. A surface low pressure system is expected to slowly develop along the front over the north-central Plains and moves towards the Great Lakes for the next couple of days. The best chance of showers and thunderstorms is expected ahead of the low pressure system over the central High Plains this evening, which will gradually spread eastward into the Midwest Wednesday night, reaching the Great Lakes and the Ohio Valley on Thursday. Some of the thunderstorms could be severe over the central High Plains tonight through Wednesday morning, along with heavy downpours that could lead to flash flooding. Over the eastern U.S., a weak frontal boundary ahead of the base of a broad upper trough is associated with a batch of showers and thunderstorms over the Mid-Atlantic into southern new England coast. These showers should move off the coast this evening as cooler and drier air from the Great Lakes moves into the Northeast and Mid-Atlantic on Wednesday. Meanwhile, typical summer heat and humidity will continue across the South with scattered showers and thunderstorms lingering along the Gulf Coast and the southeast U.S. coast where a surface trough remains in the vicinity. Out West, some showers and thunderstorms can be expected over the central Rockies. Otherwise, much of the rest of the western U.S. should be rain-free with slightly above normal temperatures through Thursday. Kong Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php