[R227R, Mammoth Mountain] topped the North American snow charts with up to 5 feet of snow delivered in 24 hours starting overnight Friday to Saturday, Dec. 17-18. The rapid-fire delivery of snow came via a storm that crashed into the Sierras, dumping snow from China Peak to North Lake Tahoe and rocketing the avalanche danger to extreme.

Skiers and riders at Mammoth woke Saturday, Dec. 18 to a 24-hour snowfall of 3.5 feet in the base area, but up to 5 feet in upper mountain elevations. The resort's snow reporter heralded it as the "storm of the year."

Snow fell so hard that Upper Panorama Gondola and several upper elevation lifts stood idle under a weather hold. Poor visibility rather than winds kept them closed for Saturday. Chains or four-wheel drives were required just to drive to Main Lodge.

"It's been dumping all day," spokesperson Deena Betcher told OnTheSnow Saturday afternoon. "The snow coming down is so thick, and the consistency is pretty heavy and dense. We haven't seen high winds yet, but they are expected tonight."

A second onslaught was expected to roll in heavy Saturday night and continue through Sunday. "We're supposed to get a small break in the storm on Monday and then it continues at least until Thursday," said Betcher. "We may not see the sky again until Friday." Temperatures hovering just below freezing are expected to keep the snow falling wet and heavy rather than light and powdery, but predicted accumulations run between 1 and 2 feet every 12 hours until Monday.

Other Central Sierra and Tahoe resorts saw less accumulation than Mammoth, but the storm's nasty side still made chains and four-wheel drive vehicles required on many roads to access resorts. [R361R, China Peak], [R34R, Bear Valley], and [R134R, Dodge Ridge] picked up 18-to-30 inches of snow by Saturday morning with a mix of rain and snow falling throughout the day.

Most Tahoe resorts woke Saturday morning to about 2 feet of fresh snow. [R299R, Northstar-at-Tahoe] picked up 27 inches at the summit, while [R419R, Squaw Valley USA] and [R201R, Kirkwood Mountain Resort] recorded 30 inches in upper elevations. By Saturday afternoon, rain pelted down, and some freezing rain clogged goggles.

Sierra Avalanche Center summed up the storm by rating the avalanche danger as high to extreme, the two highest levels of danger on the new North American scale. The snow pack makes large and very large avalanches certain; backcountry travelers should avoid all avalanche terrain. Andy Anderson, avalanche forecaster with Tahoe National Forest, pointed a finger at the weather culprits in the report: "a combination of heavy snow and rain, high winds, and a very widespread weak layer of buried surface hoar."  

"A second wave of the storm should arrive this evening (Saturday night, Dec. 18) and has even more moisture and wind associated with it," Anderson said on the Sierra Avalanche Center report. Wind gusts are expected to scream across ridges at speeds up to 125 mph. More snow is predicted by Sunday, piling up 3-to-6-feet deep depending on elevation. The freezing level is expected to waffle through Sunday around 7,000 feet.. Ski resorts and slopes below that elevation will see rain.

The National Weather Service issued a storm warning that predicted snowfall for the greater Lake Tahoe region and Mammoth area at rates of 2 to 4 inches per hour through Sunday. "Overall snowfall totals of 5 to 10 feet are likely in the Sierra above 7,000 feet," the warning said.

The warning also advised motorists to postpone travel plans to avoid dangerous travel conditions. Heavy snowfall mixed with gusty winds may produce whiteout conditions. The storm, which is expected to impact mountain passes the most, may close some roads.