Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 352 PM EDT Thu Jun 27 2013 Valid 00Z Fri Jun 28 2013 - 00Z Sun Jun 30 2013 ...Slight risk of severe thunderstorms through tonight across much of the eastern U.S., portions of the central and southern plains, and the Upper Midwest... ...Slight to moderate risk of excessive rainfall/flash flooding across portions of the Mid-Atlantic and northeastern states... ...Significant heat wave expected for much of the western U.S... The upper-level pattern across the contiguous U.S. over the short range period will become more amplified than is typical for late June, with a deep upper-level trough digging into the eastern U.S. and an anomalous upper-level ridge building across the western states. The result will be two distinctly different weather patterns across the nation. As the upper-level trough digs into the eastern U.S. and closes off as an upper-level low over the eastern Great Lakes by Friday night, surface low pressure system will move slowly from the Mid-Atlantic states tonight into northern New England by late Friday. A plume of moisture spreading into the Northeast ahead of the frontal system will produce widespread showers and thunderstorms starting tonight and continuing into Friday. Very heavy rainfall will be possible in this area; and much of the Northeast is outlined in a slight to moderate risk of excessive rainfall/flash flooding through tonight and continuing into Friday. Additional areas of scattered to widespread showers and thunderstorms will be possible along and ahead of the front into the southeastern and south central U.S. In addition to the threat of flash flooding, severe thunderstorms are also possible across a few areas of the central and eastern U.S. Please refer to the Convective Outlook products issued by the Storm Prediction Center for further information on the severe weather threat. By Saturday, much of the widespread showers and thunderstorms will be right along the East Coast, trailing southward along the frontal boundary into the coastal plain of the Southeast. As the deep upper-level trough persists across the eastern U.S., however, scattered showers and thunderstorms will remain a possibility across many areas from the Great Lakes into the southern U.S. Across the western states, the building large upper-level ridge will keep most areas dry and very hot. A few light showers may be possible through Saturday across extreme northwestern Washington, as some moisture from the Pacific streams inland. Most of this precipitation should remain in British Columbia, however. The big story across the West will be the intense heat wave beneath the upper-level ridge. Excessive heat watches and warnings have been issued by NWS local forecast offices for much of the western/southwestern states as temperatures in excess of 100 degrees will be widespread, with high temperatures potentially approaching or even exceeding 120 degrees forecast on Friday and Saturday for the hottest areas. Ryan Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php