"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.

Winter storm warnings have been issued for parts of the U.S. this Thanksgiving week—here's where snow could fall.

That's because of "another atmospheric river event" that will bring copious rainfall to coastal and valley locations and 3 to 4 feet of snow to the Sierra, forecasters said. The storm will move into the Rockies by midweek: "One tricky travel area will be in and around the Denver area as snow spreads across the area on Wednesday,

Snow is headed to the Midwest and the West ahead of Thanksgiving, while rain will target the East Coast on Thanksgiving Day.

Looking ahead to Thanksgiving, there may be issues for travelers across parts of the country due to cold temperatures and possible rain and snow across the country.

One person found dead in submerged vehicle in California as storm warning issued for Sierra Nevada through Tuesday

Across the country, snow and rain could make conditions difficult for people traveling for Thanksgiving. Rob Marciano has the forecast.