Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 442 AM EDT Sun May 12 2013 Valid 12Z Sun May 12 2013 - 12Z Tue May 14 2013 ...Slight risk of severe thunderstorms on Monday for portions of the northern Intermountain West and northern U.S. Rockies... ...Below average temperatures expected for the eastern U.S. with above average temperatures for the West... A cold front will move off the coast of the eastern U.S. into the Atlantic Ocean today, carrying the threat of widespread showers and thunderstorms with it. Portions of coastal Maine as well as Cape Cod may see the potential for showers and thunderstorms lingering into early afternoon before coming to an end. Behind the cold front a polar air mass which has already taken hold across the Midwest early this morning will filter into the eastern U.S., including the Southeast. Many areas from the Midwest to the Northeast will see the potential for freezing temperatures tonight, with low temperatures in the 30s possible as far south as the southern Appalachians. Snow is occurring this morning across portions of the Upper Great Lakes and this will continue through the morning before beginning to taper off by this afternoon. Some light snow is also possible Sunday night into Monday morning across Upstate New York as the upper-level trough crosses the region, with some enhancement from lakes Erie and Ontario. An upper-level ridge of high pressure currently over the West Coast will begin to build eastward into the central U.S. by Monday, and temperatures will warm up quickly, with above average temperatures possible by Monday across the plains. A Pacific frontal boundary will move onshore in the Northwest today, with showers and a few thunderstorms expected. The showers and thunderstorms should be relatively widespread today before becoming more scattered in nature by tonight as the front moves inland. A second Pacific front is forecast to reach the Northwest by late Monday, again increasing the coverage of showers and thunderstorms. Ryan Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php