SAN FRANCISCO (CBS SF) — A pair of winter storm systems began rolling into the San Francisco Bay Area Friday, carrying with them the promise of another weekend filled with rain showers, gusty winds and several more feet of snow in the Sierra.

A winter storm warning was to go into effect for the Lake Tahoe area at 4 p.m. Friday and stretch until Sunday night. As much as 4 feet of new snow could fall by the time systems move eastward.

“Travel could be very difficult to impossible,” the National Weather Service warned. “The hazardous conditions could impact the ski commute Friday evening and again Sunday evening. Very strong winds could cause extensive tree damage.”

The new snow totals will be adding to what it already an impressive snowpack in the Sierra. According to the California Department of Water Resources, the central Sierra which includes the Lake Tahoe area is at 126 percent of normal.

When travel is allowed in the mountain passes on 50 and 80, Caltrans warns travelers that chain controls will be in effect.

The Sierra Avalanche Center in Truckee has issued a backcountry avalanche watch for the greater Tahoe area starting at 7 a.m. Saturday until 7 a.m. Monday.

“Periods of CONSIDERABLE to HIGH avalanche danger may occur from Saturday morning into Monday morning,” the center warned. “Very dangerous avalanche conditions may occur. Travel in avalanche terrain is not recommended during HIGH avalanche danger. Large destructive avalanches could occur.”

In the Bay Area, Friday’s frontal system was predicted to drop as much as an inch of rain over an area stretching from Half Moon Bay to Santa Rosa. The California Highway Patrol warned motorists to drive with caution and expect slow travel during the evening commute.

Showers were expected into Saturday and then be followed by another round of rain on Sunday.