Avalanche danger goes up when snow falls down as heavily as it has in the Sierra this week.
Two snow slides involving people have been reported to the Sierra Avalanche Center since Tuesday.
One slide, during Thursday's big storm, carried enough snow to push a Subaru in motion across Highway 89 near Squaw Valley, according to the center's website.
No one was injured in that incident. A skier was partially buried by an avalanche near Mount Rose in Nevada on Tuesday, suffering chest and face injuries.
Up to 150 inches of new snow have fallen over the last week, with 45 inches falling in one 24-hour period at Squaw Valley.
The National Weather Service in Reno forecast up to 18 additional inches to fall at higher elevations in the Tahoe basin today.
As a result of recent heavy snows, backcountry avalanche forecasters set the danger level at 4, or high, on a five-level scale.
For a time Thursday, avalanche closure concerns led South Lake Tahoe emergency officials to change plans for handling trauma causes.
Had the need arisen, they planned to route trauma ambulances east, to Nevada hospitals, rather than taking the usual, but snow-clogged, route over Echo Summit toward Sacramento.
Most high-country visitors aren't likely to encounter avalanches. Caltrans conducts avalanche control along Highway 50 near Echo Summit – the major route with avalanche danger.
They closed the road near midnight Thursday and fired air cannons to bring down a dangerous accumulation, after which they plowed the road to let traffic to resume.
Riskier roads are usually closed when there is danger.
Highway 89 along the south part of the lake has been closed since March 16, because clearing the area is impractical.
"There are just too many avalanche chutes," said Mark Dinger, a Caltrans spokesman.
Skiers at resorts are also largely protected from avalanche danger.
Resorts' ski patrols conduct avalanche inspections before opening daily.
Where accumulations pose a risk, patrols use a ski cut – skiing across the top of a potential avalanche zone – or explosive charges to dislodge snow that could otherwise come down on skiers.
"We won't open something unless we believe it's safe," said Russ Pecoraro, communications director for Heavenly Ski Resort.
More people are bypassing resorts to ski, snowboard and snowshoe in the backcountry.
"It's hard to say (how many), but it's definitely a growing sport," said Christa Lindsey, an outdoor school instructor for REI in Sacramento.
The Avalanche Center issues its alerts for those people, covering the Sierra between Yuba and Ebbetts passes.
When it's snowing and blowing hard, avalanche danger can reach a Level 4 or 5, but that's not when most people get hurt.
"Most people die on a 2 or 3 (level day)," said Steve Reynaud, an instructor with Alpine Skills International and an avalanche observer for the Avalanche Center.
That's because people go out more once storms abate and roads are cleared to trailheads. During storms, they can't.
There have been no Tahoe-area deaths from avalanche this year. There have been 13 nationwide.
Many people now attend avalanche courses to learn how to avoid danger.
Alpine Skills teaches classes in the mountains all winter, and REI had three full beginner classes at stores near Sacramento.
"Education is the biggest tool you have," Lindsey said. "The biggest thing with avalanches is to be aware of what causes them."
Slopes around 30 to 45 degrees – "which are the fun ones to ski on in the backcountry," said Lindsey – have the biggest avalanche risk. Lindsey said she avoids the danger spots.
Backcountry travel is discouraged, unless skiers and snowboarders know how to read snow conditions and carry appropriate equipment.
Snow beacons that beam a continuous signal allow avalanche victims to be found beneath the snow.
Shovels and probes are other must-haves for backcountry snow travelers.

