Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 236 AM EDT Wed Sep 11 2013 Valid 12Z Wed Sep 11 2013 - 12Z Fri Sep 13 2013 ...Relief from the recent heat and humidity is in the forecast from the Midwest and Ohio Valley to the Mid-Atlantic and Northeast... ...Strong to severe thunderstorms will be possible from the Great Lakes into New England... ...Heavy showers and thunderstorms will persist over the Southwest...promoting additional concerns for flash flooding... After seeing a significant resurgence of summertime heat and humidity, much of the Midwest...Ohio Valley...and Mid-Atlantic states will start to see some relief as a large scale upper trough begins to amplify over the Eastern U.S. and allows for cool high pressure to settle southeast from Canada. The associated cold front leading the way for the expected drop in temperatures will serve as forcing mechanism for scattered showers and thunderstorms, which will impact the Great Lakes and Middle Mississippi Valley today and stretch ultimately into the Ohio Valley...Mid-Atlantic and Northeast on Thursday. There will be a risk of strong to severe thunderstorms along the front, with the primary threat expected to be confine to the Lower Great Lakes region and New England. Locally heavy rains cannot be ruled out either with the frontal passage where the stronger thunderstorms organize. By Friday, much cool air will have infiltrated the Eastern U.S. behind the frontal passage. Meanwhile, widespread showers and thunderstorms will continue across much of the Southwest and up across the Southern and Central Rockies and into central High Plains. These areas are expected to see additional moderate to heavy rainfall amounts, as deep monsoonal moisture interacts with energy associated with a weak upper low aloft and its associated trough axis. This coupled with upslope flow in the vicinity of the Rockies should help concentrate the shower and thunderstorm activity and will support a continued threat for flash flooding. The cloud cover will help keep temperatures relatively cool here as the rains continue through the balance of the week. Elsewhere across the southern tier of the country, moist easterly flow will support continued showers and thunderstorms across South Texas. Also there will be a weak upper low meandering over Florida which should help initiate some widely scattered showers and thunderstorms. The remainder of the South should be dry. The remainder of the nation should see pleasant and tranquil weather. Orrison Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php