The National Weather Service said "travel could be difficult to impossible" in places where snowfall is forecast to continue into the beginning of the week.

"Heavy coastal and mountain rain may lead to instances of flash flooding, particularly over the windward foothills of the southern Sierra Nevada below 8,000 feet, where excessive rainfall may cause land/rock/mudslides," the NWS said in a forecast Tuesday morning.

Parts of the Great Lakes region are seeing new snow and face the prospect of even more this week after U.S. travelers battled harsh weather to get home after Thanksgiving.