Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Fri Dec 27 2013 Valid 12Z Fri Dec 27 2013 - 12Z Sun Dec 29 2013 ...Developing storm system over the Gulf of Mexico to bring rain to the Gulf Coast states and Southeast... ...An arctic front dropping down from Canada will bring another surge of unseasonably cold air to the northern and central U.S. this weekend... ...Heavy snow possible for the upper Midwest and upper Great Lakes... Relatively mild temperatures across the Plains and Midwest on Friday will give way to yet another arctic front advancing south from Canada this weekend. Unseasonably cold air will overspread much of the northern and central U.S. in behind the front as arctic high pressure pushes down into the northern Plains. The front will also be accompanied by a band of accumulating snowfall, mainly for the northern Rockies and the northern Plains. However, the more significant snowfall potential will be Saturday and Saturday night across especially portions of the upper Midwest and upper Great Lakes region as low pressure advancing east along the front coupled with low level moisture enhancement from the relatively warmer Great Lakes helps to support the threat for heavy snow. Meanwhile, as cold air pours south from Canada for the northern and central U.S., the Gulf Coast states, Southeast and Mid-Atlantic will be warming up, and just in time as a storm system develops over the Gulf of Mexico. The storm system will begin lifting northeast up across the coastal plain of the eastern seaboard through the weekend. A large swath of rain will accompany the low center as it advances northeastward. The remainder of the U.S. should be generally dry and tranquil. The exceptions will be on Friday with some lingering lake effect snow downwind of mainly Lake Ontario. Also, the arrival of a weakening cold front in off the Pacific Ocean will bring some rain and snow shower activity to the Pacific Northwest and the northern Rockies through Friday night. The Southwest U.S. will again remain very dry and generally warm, although colder air advancing south through the Great Basin Saturday will likely result in somewhat cooler temperatures for the Southwest late in the weekend. Orrison Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php