TRUCKEE, Calif. — A strong atmospheric river made landfall early this morning and it is expected to bring heavy Sierra snow, rain, flooding possibilities and strong winds through Tuesday.

Caltrans started firing the Echo Summit cannon early Monday morning as moisture streams into the Lake Tahoe Basin. 

Schools are welcoming back students this week, but students at Donner Trail Elementary in the Tahoe-Truckee Unified School District will receive a snow day due to heavy snow at higher elevations.

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Chain controls are in effect on all mountain passes and on some highways around the basin.

For road conditions, call 511 or visit https://www.nvroads.com or https://quickmap.dot.ca.gov.

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The National Weather Service has a winter storm warning in effect through 4 a.m. Wednesday and said dangerous travel conditions are expected throughout the Sierra due to heavy, wet snow accumulation.

The advisory calls for 1 to 2 feet of snow through late Tuesday night, except 2 to 5 feet above 7,000 feet. Winds will also be strong with gusts on Sierra ridges with 130-plus gusts expected and 50 mph gusts in the basin leading to 4-foot waves on the lake.

Variable snow levels on Monday morning continue to bring “headaches to the forecast,” the service said.

“Deterministic models show snow levels bouncing between 5,500 to 7,000 feet before 10 a.m., the service said. “There remains a high boom/bust potential due to these widely variable snow levels throughout the day.”

A break in the weather is expected Monday afternoon into the evening before another wave of moisture will bring impacts early Tuesday morning.

The service said snow will reach all valley floors with 3 to 6 inches possible above 5,000 feet, 6 to 12 inches less than 7,000 feet and up to 2 feet above.

Flood and avalanche advisories were also issued.

The flood advisory was in effect through 6 p.m. Monday but the weather service eliminated that from the list of advisories on Monday morning, and the avalanche warning went into effect at 7 a.m. Monday and lasts for 48 hours.

“A winter storm with gale-force winds, high-intensity snowfall, heavy new snow accumulation, and rain on snow will result in widespread avalanche activity in the mountains,” the warning said. “Large avalanches could occur in a variety of areas.”

On Wednesday, a few more inches of snow are possible. 

The service said there is low confidence in a moderate storm affecting the Sierra on the weekend. In the extended forecast, the service said there are signals for storms to affect the west coast through the end of the month.

Bill Rozak is editor for the Sierra Sun. He may be reached at brozak@swiftcom.com.