Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 248 AM EST Thu Dec 15 2016 Valid 12Z Thu Dec 15 2016 - 12Z Sat Dec 17 2016 ...Strong storm system to bring potential for heavy rain and winter precipitation to much of the country over the next few days... ...Arctic air and strong winds will create dangerous wind chills for some areas from the northern plains to New England... A strong Pacific storm system will continue to spread moisture and precipitation from the West Coast into the Intermountain West and Rockies through Friday. A relatively warm maritime air mass has overspread much of the western U.S., with snow confined to the higher elevations from the Sierras east to the Great Basin and central Rockies today. Farther north, colder arctic air remains entrenched, and widespread snow is expected today from the northern Intermountain West to the northern High Plains. On Friday, snow levels will begin to lower across the Great Basin and the central Rockies as the main upper-level trough begins to move inland. Heavy snow is possible across a wide area including portions of the northern Intermountain West, northern Rockies, and northern High Plains today, with heavy snow possible for the central Rockies on Friday. Additionally, heavy rain will be possible along the West Coast, from southern Oregon southward through much of California. Strong and gusty winds are also possible, especially at higher elevations. Late Thursday night into Friday, the system will begin to spread precipitation east across the central U.S. Snow will be possible on Friday over a large area from the Rockies to the Great Lakes, with heavy snow possible for some areas. Farther south, warmer air aloft overspreading the shallow arctic air mass will result in the potential for sleet or freezing rain from portions of the central plains to the mid-Mississippi valley. By Friday night and Saturday morning, the system will continue to progress eastward, spreading snow into the Northeastern U.S., with freezing rain possible across portions of the Mid-Atlantic and Southeast, generally east of the Appalachians. The low pressure system will also begin to draw moisture from the Gulf of Mexico northward by Saturday, with showers and thunderstorms possible from the lower Mississippi valley to portions of the Southeast. The other notable weather story during the short range forecast period will be the frigid temperatures and wind chills across much of the northern tier. An arctic air mass will be in place today across much of the central and eastern U.S. in the wake of a cold front. Afternoon high temperatures today are forecast to be 20 to 30 degrees below average from the northern plains and Midwest to the Ohio and Tennessee valleys, Mid-Atlantic, and Northeast. These cold temperatures will persist into Friday, with only slight warming set to occur. An additional round of arctic air will begin to move into the northern plains on Friday and into the central U.S. on Saturday, with high temperatures as cold as 40 degrees below average for some areas. Meanwhile, the eastern third of the nation will warm quickly on Saturday as southerly flow ahead of the incoming storm system draws warmer air northward. Ryan Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php