Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 414 PM EDT Wed Apr 17 2013 Valid 00Z Thu Apr 18 2013 - 00Z Sat Apr 20 2013 ...Widespread heavy rainfall for the central U.S.... ...More snows from the central Rockies to the upper Midwest... A powerful system, driven by a deep upper low/trough moving out of the Rockies into the central U.S., is expected to deliver widespread showers and thunderstorms with heavy rains from the southern Plains and lower MS valley northward to the Great Lakes. As deep moisture streaming north from the Gulf of Mexico moves across a returning warm front, showers and thunderstorms will continue to fire and spread northeastward this evening from the central Plains and lower MO valley northeastward into the upper Great Lakes. As the leading edge of this precipitation spreads across the upper Great Lakes region this evening, heavy amounts are expected to redevelop back along the front over the mid MS Valley where a weak surface low is forecast to develop and lift northeastward with a deep plume of moisture in tow. As this low moves across the upper Great Lakes region as well, focusing additional showers and thunderstorms across the region overnight, a more defined surface cyclone is forecast to take shape back along the trailing front over the mid MS valley. Strengthening into a power cyclone, this system is forecast to follow a similar track into the upper Great Lakes region by Friday morning. With strong low level winds continuing to deliver moisture from the tropics, showers and thunderstorms producing heavy rains are expected to fall along a sharp trailing cold front as it sweeps across the mid and lower MS valley into the OH and TN valleys. Meanwhile, back to the northwest, closer to the track of the associated upper low, light to moderate snows are expected to spread from the central Rockies northeastward to northern MN and the Upper Peninsula of MI. In the western U.S., lower elevation rains and mountain snows are expected to spread across the Pacific Northwest into the northern Rockies late Thursday into early Friday as a weak upper disturbance moves across the region. Pereira Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php