COLUMBUS (WCMH) — Millions of Americans are expected to hit the roads and skies ahead of Christmas this week.

In parts of the United States, heavy rain, damaging winds, snow, and freezing temperatures could cause travel headaches.

In Virginia, fog and icy conditions are believed to have caused a massive pileup on Interstate 64 Sunday morning. All lanes in both directions were closed as crews cleared at least 35 vehicles from the roadway.

On the west coast, days of rain have drenched parts of Oregon and Washington. The heavy rain has pushed into the valleys of California, also bringing snow to higher elevations in the Sierra Mountains.

Down south, a storm system churning in the Gulf of Mexico is bringing heavy rain and gusty winds. In Alabama and Georgia, wind gusts could top 30 miles per hour.

More than 10 million people are under flood watches across Georgia and South Carolina, with two to five inches of rainfall possible, with some areas possibly seeing as many as eight inches of rain.

The possibility of severe storms in the southern tip of Florida is raising concerns, with damaging winds and isolated tornados being the primary threat. That system is expected to move out of the southeast by Christmas eve.

Weather will be mild and dry on Christmas day in the central U.S., the northeast and the southeast.