A storm dropped as much as 15 inches of snow in the Sierra Nevada, hastening the state of the ski season but bogging down traffic on mountain highways.

The Boreal resort atop Donner Summit reported up to 15 inches of snow from late Monday into Tuesday, and said it hopes to open Thursday. Alpine Meadows resort just north of Lake Tahoe reported as much as 14 inches of snow during the night, and hopes to open Nov. 26.

"Winter has made an entrance," said David Thatcher, snowmaking manager at Alpine Meadows.

Most Tahoe resorts typically open around Thanksgiving.

"A significant change like this in the weather pattern gets the phones ringing," said Andy Chapman, tourism director of the North Lake Tahoe Resort Association.

Chains or snow tires were required during the night on all three major highways linking Lake Tahoe and Sacramento, Calif.: Interstate 80 over Donner Summit, U.S. 50 over Echo Summit and Highway 88 over Carson Pass. Similar controls were in effect around the Reno-Tahoe area.

Farther south, Mammoth Mountain, located near Yosemite National Park, opened for the season on Monday, the first in California, after a separate storm piled up as much as 18 inches of snow during the weekend.