SOUTH LAKE TAHOE, Calif. — The incoming atmospheric river event is gathering more moisture as it barrels toward Lake Tahoe.

The National Weather Service upgraded its advisory to a winter storm warning and is calling for triple digit winds, multiple feet of high elevation snow and heavy rain which could lead to flooding and widespread travel difficulties. The service also has issued a flood watch. Both advisories go into effect at 4 p.m. Thursday and last through 11 a.m. Sunday.

The service better dialed in the snow forecast for the storm, which has been the trickiest part with snow levels fluctuating throughout the event.

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Heavy snow with periods of heavy rain will bring up to a foot of snow to Tahoe communities, and 2 to 6 feet above 6,500 feet. Winds will gust up to 60 mph and up to 120 mph along the Sierra crest. In the service’s advisory on Wednesday, 4 feet of snow was expected at the higher elevations.

The heavy snow dump will again lead to travel disruptions and possible road closures. The snow combined with wind will also create visibility problems and could cause tree damage and power outages.

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The combination of heavy rain and snow has Tahoe home and business owners scrambling to clear roofs of several feet of snow before the weighted snowpack could cause structural issues along with dangerous roofalanches.

Multiple advisories have been issued regarding snow load on roofs, including an emergency alert on Wednesday from the El Dorado County Sheriff’s Office urging roofs to be cleared and for seniors who need assistance to contact the department for possible help.

Snow levels will be fluctuating significantly, the service said. They are expected to start out around 6,500 feet Thursday afternoon and rise to 8,500 feet in the evening through Friday afternoon. Levels will drop to 6,000-6,500 feet Friday night into Saturday.

The atmospheric river will soak the deep snowpack and the service said rain may pass through during the prolonged event bringing a substantial hazard of flooding which may occur in poor drainage and urban areas due to deep snow confining flow and limiting drainage. 

Free sandbags are available in South Lake Tahoe behind the fire station at 2101 Lake Tahoe Boulevard. Sand, shovels, sandbags and filling station are all available to use.

The active weather will continue later in the weekend and into next week, the service said.

The steady heavy precipitation will begin to taper back on Saturday afternoon but almost continuous snow showers are expected in the Sierra. Another 1 to 2 feet of snow is possible from late Saturday to Monday along the Sierra crest with light accumulations at lake level.

The active weather is expected to continue beyond Monday with more rain and snow possible.