Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 258 PM EST Tue Dec 13 2016 Valid 00Z Wed Dec 14 2016 - 00Z Fri Dec 16 2016 ...Arctic air mass poised to overspread much of the north central and northeastern U.S... ...Pacific storm system to bring a prolonged period of potentially heavy rain and snow to the western U.S... A frontal system moving across the East this afternoon is bringing snow from the Great Lakes east to the Mid-Atlantic and Northeast. Much of the northern Mid-Atlantic and Northeast will remain cold over the next couple of days as the airmass remains entrenched along the northern portions of the Appalachians. Another round of snow, possibly heavy for areas downwind of the Great Lakes, is expected Wednesday afternoon through Thursday as another Canadian cold front moves through. The southern flank of this system will bring widespread rain to the southern Mid-Atlantic and Southeast, possible heavy across southern Georgia and coastal areas of the Carolinas. The northern Plains and Upper Midwest will remain frigid through the end of the work week as a fast-moving arctic frontal boundary surges southward. Forecast highs for Wednesday will range from 20 to 30 degrees below average for much of the northern plains and the Upper Midwest. This is the same system that will bring widespread snow from the Great Lakes to the Northeast on Thursday. Surface high pressure over a majority of the central Plains and Mississippi valley will keep much of the central U.S. dry, but rather cool. Widespread precipitation is forecast for much of the northern half of California, the Pacific Northwest and the Inter-mountain West as a Pacific low pressure system, accompanied by an expansive plume of moisture, moves inland. Rain, likely heavy at times, is forecast for northern California and southwest Oregon may result areas of flooding over the next few days. The snow levels will rise Wednesday evening through Thursday as warmer air advects into the region. The rain will quickly transition to a wintry mix near the Cascades and Sierras. Cold air trapped in the valleys of the northern Great Basin and Inter-mountain West will allow precipitation to fall as snow. Significant snow accumulations will be possible across portions of the Great Basin, northern Inter-mountain West, and Pacific Northwest, along with some ice accumulations in valleys. Additionally, flooding rains are possible across much of central and northern California. The threat for heavy precipitation is expected to persist into Thursday as multiple waves of low pressure move along the frontal boundary into the West Coast. Please refer to products issued by your local NWS forecast office for further details specific to your area. Campbell Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php