Heavy snowfall and high winds are forecast Wednesday in the Lake Tahoe area, and travel will be “very difficult,” the National Weather Service said.

A winter storm warning is in effect through 1 a.m. Thursday in the northern Sierra Nevada, from the Mount Lassen area to Yosemite. Snow accumulations of 12 to 18 inches are forecast for Truckee and South Lake Tahoe, with up to 30 inches on the highest Sierra peaks. Gusty winds could exceed 100 mph on the ridges, the weather service said.

There is a high chance of snow squalls — snowfall of around 1 inch an hour, accompanied by winds — Wednesday afternoon at Tahoe and Wednesday evening in the Mammoth Mountain area.

Chain controls were in effect Wednesday morning on Interstate 80 between Nyack and Truckee and on Highway 50 between Strawberry and South Lake Tahoe. Vehicles in both directions must have chains, unless they have four-wheel drive and snow tires.

Snow is expected to decrease around 6 p.m. Wednesday, and driving conditions will be better on Thursday, though there is a risk of flash freezes causing icy roadways, the weather service said.