Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 435 PM EDT Mon Aug 12 2013 Valid 00Z Tue Aug 13 2013 - 00Z Thu Aug 15 2013 ...Heavy rain and flash flooding possible across Oklahoma and the Lower Mississippi Valley... ...Noticeable cool-down in the forecast for the Great Lakes...Ohio Valley...and northern Mid-Atlantic States... Widespread showers and thunderstorms will continue to develop along and to the south of a frontal boundary stretched all the way from the Central Plains to the Mid-Atlantic states. Impulses of energy aloft should help ignite some organized areas of strong to potentially severe convection...and given the amount of moisture in place to the south of the boundary...heavy downpours will be possible within the developing storms. The greatest threat for any flash flooding will be across Oklahoma and eastward into a good portion of the Lower Mississippi Valley. By early Tuesday...a large area of high pressure building in over the north central U.S. will finally help push the boundary southeastward towards the Eastern Seaboard and Gulf Coast. Strong to severe storms containing heavy downpours will still be a possibility with the passing front...but noticeably cooler and drier air will quickly fill in behind it. Conditions will become especially cool across the Great Lakes...Ohio Valley...and northern Mid-Atlantic States...where northwesterly flow within a broad trough aloft will be bringing in reinforcing shots of Canadian air. Out west...the western portion of the front pressing southeastward towards the Atlantic and Gulf coasts will stay banked up against the terrain of the central and northern Rockies. The front will serve as a focal point for showers and thunderstorms across the Rockies and adjacent High Plains. The northwestern corner of the Nation should stay precipitation free for the next few days...but some showers from an approaching Pacific cold front could infringe upon the coastal regions by the end of the forecast period. Gerhardt Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php