Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 245 PM EST Fri Dec 29 2017 Valid 00Z Sat Dec 30 2017 - 00Z Mon Jan 01 2018 ...Reinforcing shot of bitter cold arctic air to bring temperatures to near or below zero across much of the northern Plains this weekend... ...Moderate to heavy lake effect snows will continue downwind of the Great Lakes... ...Heavy snowfall likely into Saturday across the higher terrain of the Northwest... The dominating weather story as we head into the weekend continues to be the cold air mass persisting across much of the country east of the Rockies with afternoon high temperatures of 5 to 10 degrees below normal. Meanwhile, a clipper type of system is expected to send a swath of light snow from the Midwest this evening, into the northern Mid-Atlantic on Saturday with only light accumulations expected. Across the Great Lakes, westerly flow on the backside of this system will allow for moderate to heavy lake effect snows to continue downwind of the lakes with localized totals of 6 to 12+ inches possible. In the wake of this cold front though, another reinforcing shot of very cold arctic air from Canada will drop into the northern Plains by Saturday. This will bring daytime high temperatures plunging to near or below zero readings this weekend, which is 30 to 40 degrees below normal for this time of the year. This air mass will spread eastward on Sunday with parts of the Northeast and Mid-Atlantic expected to be near 20 degrees below average. Out west, heavy snowfall will continue tonight and into Saturday across the northern Intermountain West and the northern Plains as upper level energy moves through in the flow aloft. Winter storm warnings and winter weather advisories are in effect with additional snowfall accumulations of 1 to 2 feet possible in the highest terrain. The heavy rainfall across coastal regions of the Pacific Northwest should come to an end this evening as the associated cold front moves onshore. Finally, a developing wave of low pressure in the western Gulf of Mexico will bring light rain into eastern Texas tonight and spreading into the Lower Mississippi Valley and central Gulf States by Sunday. Some mixed precipitation or freezing rain will also be possible on the northern edge of the moisture shield from northern Texas to central Mississippi and Alabama. Santorelli Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php