Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 318 AM EDT Tue Sep 09 2014 Valid 12Z Tue Sep 09 2014 - 12Z Thu Sep 11 2014 ...There is a slight risk of severe thunderstorms from the central Plains to the mid and upper Mississippi Valley Tuesday, continuing into the Great Lakes and Ohio Valley Wednesday... ...Heavy rain possible from parts of the Upper Great Lakes to the Middle Mississippi Valley... ...Heavy rain possible Tuesday over the southwest to the southern Great Basin and parts of Central Rockies... An area of low pressure will develop in the central Plains Tuesday night and move northeast into the upper Mississippi Valley and then the upper Great Lakes by Wednesday. Moisture will move northward over the Plains to the Middle Mississippi Valley to combine with ascending motion to produce showers and thunderstorms from the central Plains to the Middle/Upper Mississippi Valley by Tuesday evening and in the Great Lakes and Ohio Valley Wednesday. Both a severe weather threat and excessive rainfall threat exist in the mid-upper Mississippi Valley to the Great Lakes. Monsoonal moisture will also aid in producing showers and thunderstorms over parts of the Southwest/Southern California into parts of the Great Basin and the Central/Southern Rockies on Tuesday. Flash flood watches remain in effect in these areas. As drier air aloft filters into the region, coverage and amounts of rain will decline on Wednesday. A front extending from the Upper Mississippi Valley to the Northern Rockies will move southward to the Central Plains and eastward to the Upper Great Lakes. Cold air behind the front will aid in the development of snow over parts of the Northern Rockies through Wednesday. In addition, upslope flow associated with high pressure over Western Canada will aid in producing rain showers over parts of the Northern Plains Tuesday night into Wednesday. Meanwhile, low pressure moving along a stationary front along the mid Atlantic coast will produce showers and thunderstorms through Tuesday night, then move offshore through Wednesday night. Diurnal showers and thunderstorms will also develop over parts of the Central/Eastern Gulf Coast to Florida both Tuesday and Wednesday. Petersen Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php