Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 400 PM EDT Fri May 19 2017 Valid 00Z Sat May 20 2017 - 00Z Mon May 22 2017 ...Heavy rain associated with strong to severe thunderstorms could lead to flash flooding over the central/southern Plains tonight... ...Heavy rain could move into the Mississippi Valley and the Midwest on Saturday... ...Snow ending over the central Rockies... A late-season snowfall event is ending over the central Rockies as the associated cold upper low drifts slowly towards the northern Plains. Ahead of the upper low, a surface low pressure system has been developing along a frontal boundary over the central Plains. Moist and unstable air continues to stream northward ahead of the low. With favorable upper-level dynamics in place, areas across the central Plains will remain the focus for strong to severe thunderstorms through tonight. The rain could become heavy enough to cause areas of flash flooding. Farther to the east, very warm to hot weather along the East Coast in the last couple of days will be replaced by much cooler conditions, thanks to the passage of a rather sharp back-door cold front. Expect scattered thunderstorms early this evening followed by a chance of light rain or drizzle across the mid-Atlantic later tonight. This will be followed by overcast conditions through much of the weekend. The low pressure system over the central Plains will consolidate and move steadily northeastward, reaching the Great Lakes on Sunday. Showers and thunderstorms ahead of the system will then spread northward up the Mississippi Valley, into the Ohio Valley and the Midwest on Saturday, whereas mainly rain is expected to reach the upper Midwest and upper Great Lakes on Sunday. Meanwhile, showers and thunderstorms will edge slowly into the interior southeastern U.S. and along the Gulf Coast on Sunday. Meanwhile, upper-level energy moving southeastward from British Columbia will bring scattered showers and high-elevation snow showers across the Intermountain Region and northern Rockies on Saturday, reaching the central Rockies later on Sunday. Kong Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php