Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 153 PM EST Fri Dec 18 2020 Valid 00Z Sat Dec 19 2020 - 00Z Mon Dec 21 2020 ...Lower elevation rain and higher elevation snow continues across the Northwest... ...Light snow is possible across the Central Rockies/High Plains and Great Lakes region, while showers/thunderstorms will affect the south-central U.S. beginning late Friday... ...Cold temperatures in the Northeast to return to more seasonal levels by Sunday... An active weather pattern looks to persist through the weekend across the Pacific Northwest and Northern Rockies as wave after wave of low pressure systems usher in Pacific moisture to these regions. Coastal and lower elevations can expect rain while the mountainous terrain see snow that will fall heavily at times. A cold front is forecast to reach the western coast of Washington this afternoon bringing a swath of precipitation extending from the International border on south into Oregon. Precipitation associated with this frontal system then reaches the northern Rockies tonight and Saturday morning where snow is likely to be the primary precipitation type. A brief lull in the action near midday in the Pacific Northwest gives way to yet another Pacific storm directing another round of moisture towards the region with heavier precipitation amounts than the first. By Sunday, heavy snow reaches the northern Rockies along with strong winds. In fact, much of the northern Rockies and Plains are in for a windy weekend, some of which could be quite intense. As a result, High Wind Watches and Warnings have been issued for parts of central Montana and southeast Wyoming. In total, 1 to as much as 3 feet of snow is expected in the Washington Cascade and Olympic ranges. The interior mountain ranges of the northern Rockies such as the Sawthooths, Bitterroots, and Tetons can expect totals over a foot of snow as well. Meanwhile, coastal and lower elevations of the Pacific Northwest can expect 1 to 2 inches of rainfall with the highest totals along the coastal ranges of western Washington and Oregon where rainfall amounts may reach as high as 5 inches. An upper-level trough axis in the Four Corners region, into the central U.S. Saturday, and toward the Ohio Valley by Sunday morning. Associated with this trough, some light snow is possible across the Central Rockies today, while light mixed precipitation could also spread across the Central Plains. Then tonight into Saturday, rain showers and thunderstorms are expected to increase in coverage and intensity across the southern portions of the Plains and Mississippi Valley as Gulf of Mexico as the frontal system taps into rich Gulf of Mexico moisture. Also, farther north, a separate upper level disturbance is set to produce a round of light snow across the Upper Midwest today, then by Saturday, generate rain and snow showers over the Great Lakes region Saturday. Snow totals are expected to remain less than 2 inches there. Precipitation is forecast to push eastward into the Ohio and Tennessee Valleys late Saturday and toward the Eastern Seaboard Sunday. By Sunday evening showers will reach the Deep South and Ohio/Tennessee Valleys while spotty rain and snow shores track across the eastern Great Lakes and northern Mid-Atlantic. In the East, the historic nor'easter has pulled away from the coast and high pressure has arrived in its wake. This cold Canadian high pressure system will keep below normal temperatures entrenched up and down the Eastern Seaboard, likely staying below freezing in much of the Northeast this evening and Saturday thanks in part to the fresh snow-pack throughout the region. In fact, lows Saturday morning appear to be bitterly cold in the interior Northeast with temperatures in the single digits. High pressure slides east off the coast on Sunday allowing for the return of more seasonal temperatures as well as a chance for wet weather late in the day on Sunday. Other regions likely to witness below normal temperatures are the Intermountain West and Southeast. On the flip side, abnormally mild weather sets up shop in the North Central U.S. where temperatures of 10 to 20 degrees above average are forecast. Mullinax Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php