Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 436 AM EDT Tue Aug 27 2013 Valid 12Z Tue Aug 27 2013 - 12Z Thu Aug 29 2013 ...Late summer heatwave continues across the north central U.S.... ...Storms containing heavy downpours and severe weather possible from the Upper Great Lakes to the Central Appalachians... ...Widespread threat for flash flooding has diminished across the Southwest... A late summer heat wave will continue across the north central U.S. the next few days...underneath an expansive upper ridge anchored over the Central Plains and Middle Mississippi Valley. Excessive heat warnings and heat advisories remain in effect over a large portion of the Upper Midwest...where uncomfortably high temperatures and dew points will combine to create triple digit heat indices. â€In addition to the heat...weak energy rippling through the northern periphery of the upper ridge will help fire up convection while it tracks from the Upper Great Lakes to the Northern Mid-Atlantic. These storms will be developing in an environment ripe for organization...making heavy downpours and severe weather a possibility. A second piece of energy beginning to round the northern fringe of the upper ridge should help ignite convection across the Dakotas Wednesday evening. To the south of the expansive upper ridge...additional days of scattered showers and thunderstorms are expected across Florida as well as South Texas. Out west...energy rotating through an upper trough stationed over the northeast Pacific will bring surges of moisture and steady rains into coastal areas of the Pacific Northwest Tuesday and Wednesday. Farther south...the widespread threat for flash flooding has just about diminished across the Southwest. However...plenty of moisture getting pulled northeastward in-between the expansive ridge over the Central U.S. and the upper trough in the northeast Pacific will fuel numerous showers and thunderstorms over the Southwest...Great Basin...and Central Rockies. Some of these storms could contain moderate to locally heavy rains. Gerhardt Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php