Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 210 AM EST Sat Dec 17 2016 Valid 12Z Sat Dec 17 2016 - 12Z Mon Dec 19 2016 ...Strong storm system will affect the southern and eastern U.S. this weekend... The weather pattern this weekend will continue to be quite active with a strong low pressure system currently over the central Rockies and another surface low over the Ohio Valley. A fresh surge of arctic air is flowing southward from western Canada and this will reinforce the very cold conditions already in place across the northern tier states for a few more days. The arctic front will join forces with the low pressure area traversing the Ohio Valley and Great Lakes region. A tremendous temperature gradient is expected in the vicinity of the front across Oklahoma and Texas, with 60s and 70s south of the front, and sub-freezing temperatures behind it. Readings could fall as much as 25 degrees in one hour with the cold frontal passage! The cold weather currently across the eastern U.S. will modify quite a bit on Saturday as the aforementioned storm system across the Ohio Valley lifts northeastward towards the Great Lakes region. The warming trend will likely be heralded by some snow and mixed wintry precipitation across parts of the northern Mid-Atlantic region and the interior Northeast, before changing to rain later in the day. Some cold air damming is likely near the Appalachian Mountains with a shallow layer of cold air in place Saturday morning, before strong southerly winds aloft erode this cold layer by Saturday evening. A brief period of mild weather can be expected Saturday night and early Sunday before colder weather arrives in time for the beginning of the work week for the East Coast. A large and expansive surface high should establish residence across much of the central U.S. on Sunday and also across much of the West. Once the front clears the coast, a quieter weather pattern is likely to commence. D. Hamrick Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php