New snow and strong winds have formed wind slabs on a variety of sliding surfaces including sun crusts and faceted snow. Since Tuesday night in the Greys River area, there have been about 18 inches of snow with 2 inches of snow water equivalent and strong southwest to west winds. Last night and early this morning WYDOT triggered large slab avalanches that ran across the Teton Pass roadway from 3 separate slide paths. Along with wind slabs, weak snow near the base of the snowpack could also fail, resulting in large persistent slab avalanches. Larger triggers such as cornice drops, snow machines, or a surface wind slab could trigger these persistent wind slab. Below an elevation of 7,500 feet, isolated pockets of soft slabs could be triggered in steep wind loaded avalanche starting zones. Cautious route-finding and conservative decision making are essential for safe travel in avalanche terrain today.
Strong west winds continue to transport new and recent snow into avalanche starting zones on leeward aspects. These slabs will be sensitive to backcountry travelers on all aspects. Slab depths could be one to three feet with the deeper depths favoring the upper elevation avalanche starting zones.
Above 8,500 feet, weak snow lies near the base of the snowpack. This weakness is most likely to be found on northwest through northeast aspects although it does exist on other aspects at the higher elevations. New snow is stressing this layer, making it more susceptible to failure. Crown depths could be up to five feet and if triggered, it would be difficult to survive one of these hard slab avalanches.
( Discussion is generated from the previous day's afternoon forecast. )Snowfall will become lighter after midnight and continue through the day. Additional accumulations of 4 to 8 inches are likely at the higher elevations with another 2 to 4 inches possible in the valleys. Westerly winds will continue with gusts from 35 to 45 miles per hour over the peaks on Thursday. Temperatures will be in the teens in the mountains and in the 20's in the valleys.Conditions are expected to be dangerous at the mid and upper elevations and in some steep active avalanche starting zones at the lower elevations. Westerly winds have formed new slab avalanches up to 30 inches in depth that can be triggered by humans and release naturally in steep wind loaded avalanche starting zones. Full depth avalanches can also be triggered by these surface slabs or by the weight of a person or a snowmachine. These dangerous slabs could be 3 to 5 feet deep. Expert terrain assessment and route finding skills will be essential for safe travel in avalanche terrain. The general avalanche hazard is expected to be considerable at the mid and upper elevations (7,500 to 10,500 feet) and moderate below an elevation of 7,500 feet.
