Avalanche conditions remain dangerous at the mid and upper elevations. Yesterday in Grand Teton National Park, backcountry travelers triggered two large avalanches on southeasterly to easterly aspects between 7,500 and 8,000 feet. These slides likely failed on faceted layers, and similar persistent slabs could be triggered today. The likelihood of triggering these slabs will slowly rise as new snow increases the load on these weak layers. Skiers and riders still have some potential to trigger small to large wind slabs in steep, wind loaded terrain at the mid and upper elevations. Don’t let the abundant powder and the holiday weekend impair your judgement; conservative terrain choices and careful snowpack evaluation will be necessary for safe travel in avalanche terrain.
In steep, wind loaded terrain at the mid and upper elevations, skiers and riders could trigger wind slabs ranging in depth from 1 to 3 feet. As the day progresses, stronger winds and new snow will slowly increase the likelihood of triggering these slabs along with the development of small, new wind slabs.
Between 1.25 and 2.0 inches of snow water equivalent has been added to persistent weak layers in the snowpack since Thursday evening, and an additional half of an inch of water weight could be added by the end of the day. In the higher elevations, these faceted layers are deeply buried, mostly rounded and unlikely to be human triggered. At the mid and lower elevations, where the snowpack is shallower, these weak layers are more pronounced and easier for skiers or riders to impact. These persistent slabs are likely to range in depth from 2 to 4 feet, and could also step down from the release of a wind slab.
Snow is forecast to continue overnight and into Tuesday with decreasing intensity after sunrise. Additional accumulations of 10 to 18 inches are possible in the Tetons and in portions of the Greys River areas. Five to 8 inches are possible in the Togwotee Pass area. Temperatures will be in the teens in the mountains and in the 20’s at the lower elevations. Summit winds are forecast to be from the west at 15 to 20 with gusts to 30 miles per hour.New snow continues to increase the load on buried weak layers. As we tetter on the brink of failure on these problem layers conditions will be dangerous. Large to very large slab avalanches are likely to be triggered by humans. Naturally released avalanches are possible and could run long distances. Large avalanches involving only the most recent new snow could be 1 to 3 feet deep. Very large avalanches that fail on deeper layers will be destructive and could be up to six feet deep. The general avalanche hazard is expected to be considerable and may increase to high in areas where copious amounts of new snow has accumulated on a snowpack with reactive, persistent weak layers. Being caught in a very large avalanche tomorrow is likely to be un-survivable. Expert route selection skills will be necessary for safe travel in avalanche terrain tomorrow.
