Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 308 AM EDT Fri Apr 28 2017 Valid 12Z Fri Apr 28 2017 - 12Z Sun Apr 30 2017 ...Severe thunderstorms and flash flooding possible from portions of the southern plains to the Ohio valley... ...Heavy snow possible for portions of the Rockies and the High Plains... ...Above average temperatures expected for much of the eastern U.S... An active weather pattern is expected to persist from much of the central U.S. into the Ohio valley through the next few days, with hazards ranging from severe thunderstorms and flash flooding to heavy snow. A frontal boundary is forecast to linger from the southern plains to the mid-Mississippi and Ohio valleys into the weekend as multiple waves of low pressure traverse the boundary. A deepening upper-level low moving from the Rockies into the southern plains will keep deep southerly flow in place across the central U.S., transporting abundant moisture northward for precipitation. Scattered to numerous showers and thunderstorms are expected today through Sunday for much of the southern and central plains, the Mississippi valley, and the Ohio valley. Severe thunderstorms and flash flooding are both possible from portions of the southern plains to the Ohio valley today and Saturday. Please refer to products issued by the Storm Prediction Center for further details on the severe weather threat. Cold air on the northwestern side of the system will produce a mix of rain and snow from the Rockies into portions of the northern and central High Plains today. Heavy snow is possible for some areas in the central and northern Rockies as well as the adjacent High Plains. As colder air spreads south on Saturday, rain is expected to change to snow across the southern Rockies as well as portions of the southern High Plains, with heavy snow once again possible for some areas. Across the eastern U.S., high pressure at the mid and upper levels of the atmosphere will support well above average temperatures. High temperatures today and Saturday are expected to be 10 to 20 degrees above average for some areas. A cold front may produce some scattered showers and thunderstorms across the Mid-Atlantic region Saturday afternoon into Sunday. Ryan Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php