Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 418 AM EDT Mon May 18 2015 Valid 12Z Mon May 18 2015 - 12Z Wed May 20 2015 ...Dry and cooler conditions developing across the northern Great Plains and upper Midwest... ...Showers and thunderstorms shifting east across the eastern U.S. ahead of a well-defined cold front... ...Widespread showers and thunderstorms across the West... ...By early Tuesday heavy precipitation developing across portions of the central and southern High Plains... Precipitation, including some wet snowflakes, will continue to diminish across the Dakotas and northern Minnesota on Monday as a strong low pressure system continues to track across northern Minnesota before reaching southwestern Ontario later in the day. In the wake of this system, dry and colder conditions will develop across much of the northern Great Plains and upper Midwest on Monday as cold high pressure drops south from Canada. Forecast highs are expected to be several degrees below normal across much of the region. Behind a well-defined cold front, this colder air is forecast to spread further to the south and east, with temperatures staying below their normal highs across much of the central U.S. and Midwest on Tuesday. In the warm, moist air ahead of the front, expect showers and thunderstorms to fire, falling from Texas northeastward through the lower Mississippi, Tennessee and Ohio valleys into the eastern U.S. on Monday; refocusing further to the south and east as the front continues to progress on Tuesday. In the West -- showers and thunderstorms are expected across a large portion of the Pacific Northwest, northern California, the Great Basin and parts of the Southwest on Monday as a deep upper-level system settles into the southwestern U.S. Showers and thunderstorms, falling in the form of snow across the higher elevations, are expected to spread across the central and southern Rockies as this upper system continues to shift east across the Southwest late Monday into Tuesday. By early Tuesday, the threat for organized heavy rains is expected to increase along the eastern front of the central and southern Rockies into the High Plains as moist and unstable air from the Gulf of Mexico is drawn north ahead of the approaching upper level system, supporting showers and thunderstorms across the region. Pereira Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php