Slab avalanches that were triggered by skiers and snowmoblers in the Teton and Snake River Ranges on Friday and Saturday were some of the larger events of the season. One of these avalanches was remotely triggered by a skier in Grand Teton National Park. Another avalanche in the Snake River Range caught four snowmobilers. One did not survive. Northwest winds were strong overnight and continued to load leeward aspects. Persistent weak layers continue to be potential problem layers in some areas at all elevations and aspects. Large slab avalanches could be triggered by humans who venture onto steep avalanche prone slopes. Snowpack collapses are a sign of instability. In these conditions the consequences of a poor terrain choice could be severe. Expert route finding skills and conservative terrain choices are essential for safe travel in avalanche terrain.
Strong northwesterly winds have loaded lee slopes and cross loaded gullies and other terrain features. Slab avalanches formed by those winds could be triggered by humans in steep wind loaded avalanche starting zones. These slabs could be up to two feet deep at the mid and upper elevations and up to 18 inches deep below an elevation of 7,500 feet
On steep avalanche prone slopes, large persistent slab avalanches could fail on buried weak layers of faceted snow. These dangerous slabs could be two to four feet deep at the mid and upper elevations and 1 to 2 feet below an elevation of 7,500 feet. These slabs could be triggered by the weight of a single person or by the release of a wind slab.
( Discussion is generated from the previous day's afternoon forecast. )A cold front will bring colder air to the region. Snow showers are possible overnight. On Monday temperatures will be in the single digits. Skies will become mostly sunny. Northwesterly winds will decrease to 10 to 15 miles per hour.Persistent weak layers continue to be failure planes for avalanche release. These weak layers include buried layers of surface hoar in areas with a deeper snowpack and a base of well-developed faceted snow in areas where the snowpack is less than four feet deep. Large slab avalanches could be triggered by backcountry travelers who venture onto steep avalanche prone slopes. These dangerous slabs could be 2 to 4 feet deep at the mid and upper elevations where the general avalanche hazard is expected to be considerable and up to two feet deep below an elevation of 7,500 feet where the general avalanche hazard is expected to be moderate.
