Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 259 PM EST Wed Dec 14 2016 Valid 00Z Thu Dec 15 2016 - 00Z Sat Dec 17 2016 ...Pacific storm system to bring a multi-day period of potentially heavy rain and snow to the western U.S... ...Arctic air mass poised to overspread much of the north central and northeastern U.S... Much of the West will remain in an active wet pattern over the next few days. A nearly continuous stream of moisture will interact will a Pacific low pressure system pushing inland across northern California and the Pacific Northwest; which will spread rain and mountain snow from the West coast to Great Basin/Intermountain West. Snow levels will raise during the overnight hours and into Thursday morning as warm air lifts into the region. Areas along and north of the advancing warm front may have mixed precipitation (rain/snow, freezing rain and/or sleet); primarily at lower elevations where cold air could remain trapped for a longer period of time. The upper-level trough associated with this storm system is forecast to push further inland Thursday night and into Friday; which will cause the snow levels to lower again across the Pacific Northwest. Heavy mountain snow and valley rain will also spread into the central Rockies by Thursday night and Friday - some locations may have significant snow or ice accumulations. Further to the south, flooding rains will be possible across much of central and northern California. Please refer to products issued by local NWS forecast offices for further details specific to your area. Surface high pressure, moving southward through the Great Plains/Midwest in the wake of a fast-moving cold front, will allow arctic air to overspread much of the central and eastern states. Forecast highs are expected to be 20 to 30 degrees below average over the north-central tier of the U.S. The passage of the cold front will help generate another round of heavy snow/lake effect snow of the Great Lakes region and areas downwind. Another arctic high sliding southward into the High Plains will bring another surge of frigid air into the northern High Plains. Moisture associated with the western U.S. storm system will begin to overspread the central U.S. - generating snow Thursday night into Friday for the northern plains, with mixed precipitation possible across the central plains. Campbell Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php