Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 359 PM EDT Mon May 09 2016 Valid 00Z Tue May 10 2016 - 00Z Thu May 12 2016 ...Strong to severe thunderstorms possible from the southern and central Great Plains to the lower and mid Mississippi Valley... ...Heavy rainfall accumulations possible for portions of the Midwest and northern High Plains... ...Locally heavy snows possible for portions of the northern Rockies into Tuesday... Warm, moist air transporting northward from the Gulf of Mexico is fueling the convection ahead low pressure system crossing the southern Plains and low pressure system that is moving from the Central into the central Great Plains. Scattered to widespread showers and thunderstorms spanning from the northern High Plains to the lower and mid Mississippi Valley will continue through night and into Tuesday. Periods of heavy rain are expected across the eastern half of Montana, which will increase the threat for flash flooding and river flooding. An excessive rainfall outlook has been issued for this area. Some of these storms may be strong to severe, particularly from northeast Texas, southeast Oklahoma into Arkansas and northwest Louisiana, where the air mass is expected to become highly unstable as well. The Storm Prediction Center has identified this area as having an enhanced risk for severe thunderstorms. Moisture spreading further to the north is likely to focus along a slow moving frontal band -- supporting widespread moderate to locally heavy rainfall accumulations across portions of the lower Missouri and mid Mississippi valleys. Excessive rainfall will be possible through Tuesday mornig from Arkansas northeastward to the Iowa and Illinois border. Organized showers and thunderstorms are expected to focus along the frontal boundary that will continue to extend from the mid Mississippi into the Ohio valley and Mid-Atlantic states. Back to the west, a well-defined cold front is forecast to drop through the western U.S. this period, with below-average temperatures spreading south and east from the northern Rockies and High Plains. Moderate to heavy precipitation is likely to develop west of an organizing area of low pressure over the northern High Plains. Heavy rain accumulations are expected to center over eastern Montana, with heavy mountain snows over the ranges of southwestern Montana and northwestern Wyoming. Campbell/Pereira Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php