Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 356 AM EDT Mon Mar 20 2017 Valid 12Z Mon Mar 20 2017 - 12Z Wed Mar 22 2017 ...Moderate to heavy snow possible over the Sierras... ...Heavy rain over parts of Northern California... Showers and thunderstorms are forecast from the Mid-Mississippi valley to the Mid-Atlantic/Northeast today and Tuesday as a low pressure system tracks east across the central U.S. Snow or possibly a mix of rain and snow will spread across portions of the Northern Plains and the Great Lakes/Northeast as Arctic air spills into the northern tier states. Much of the West Coast will be in an active wet pattern through at least midweek as a cold front advances toward the coast. Rain will become widespread from central California to Washington and may be heavy at times -- especially for northern California. Higher rainfall rates/intensity may lead to rapid runoff... flash flooding may develop. During the overnight hours snow will develop over the Cascades and Sierras and will spread east to the Northern Rockies on Tuesday. The Sierras will likely have heavy snow on Tuesday and Wednesday. Campbell Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php