Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 318 AM EST Fri Dec 29 2017 Valid 12Z Fri Dec 29 2017 - 12Z Sun Dec 31 2017 ...Heavy snowfall likely in the higher terrain of the northern Intermountain West and northern Rockies... ...A reinforcing surge of arctic air is forecast to overspread much of the eastern two-thirds of the U.S. this weekend... A cold weather pattern is expected to persist through the weekend. Much of the country east of the Rockies has already been in the grip of an arctic air mass. Another reinforcing shot of arctic air is currently taking shape over northwestern Canada as the associated strong high pressure system is forecast to slide southeastward and dominate the weather pattern across the U.S. mainland through the weekend. Meanwhile, heavy snow is expected to fall across the Cascades and into the northern Rockies today before gradually tapering off on Saturday as moisture from a Pacific system moves over the cold and dense arctic air at the surface. As much as 2 to 3 feet of snow is possible in the highest terrain of the Washington Cascades and the northern Rockies before ending Sunday morning. Farther to the west, heavy rainfall can be expected for coastal regions of the Pacific Northwest today into tonight. A clipper type system is expected to send a swath of light snow rapidly from the Dakotas into the Midwest today, across the Ohio Valley tonight, and into the northern Mid-Atlantic on Saturday with only light accumulations expected. In the wake of this clipper system will be the arrival of a reinforcing surge of arctic air from Canada, sending temperatures down to as much as 30 to 35 degrees below normal with below zero readings as far south as Nebraska. Meanwhile, a wave of low pressure is expected to bring light rain into eastern Texas tonight, spreading eastward into much of the central Gulf states by Sunday. Some mixed precipitation can be expected near the northern edge of the moisture shield across northern Texas into Arkansas and central Mississippi. Elsewhere, lake-effect snowfall can be expected to continue downwind of the Great Lakes. Kong Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php