Yesterday’s storm brought 6 to 12 inches of new snow to the Tetons. Up to three feet of snow has fallen since December 11. Persistent weak layers exist at the interface beneath this new snow and old snow surfaces that formed during a long dry period. On avalanche prone slopes, the weight of a single person could trigger a slab avalanche on this interface. At the mid and upper elevations these slabs could be large enough to seriously injure or fully burry a person. This persistent weak layer was especially active yesterday between an elevation of 7,800 and 7,300 feet. The slides that occurred in this elevation zone were smaller than what you might trigger up higher where new snow depths are greater. This type of hazard is best managed by terrain assessment skills and conservative terrain choices. Evaluate steep slopes carefully and anticipate the potential consequences of triggering a slab avalanche of any size above terrain traps or on slopes with low snow hazards that can cause serious trauma.
At the mid and upper elevations large slab avalanches formed by southwest to west winds could be human triggered. These slabs could be two to three feet deep. Slab avalanches triggered at the lower elevations are likely to be a foot deep.
Overnight, a transitory ridge of high pressure will build ahead of a fast-moving short wave trough. Cloud cover is expected to increase, and by tomorrow morning, skies should be mostly cloudy. Light snowfall will develop across Western Wyoming with accumulations of one to four inches. Mountain temperatures will be in the teens and valleys should climb into the twenties. Westerly ridgetop winds are expected to be 15 to 20 miles per hour with higher gusts. The general avalanche hazard above 8,000 feet is expected to be Moderate. Skiers and riders could trigger slab avalanches one to two feet deep, where these slabs lie over persistent weak grains. The snowpack structure across the forecast area varies, and where a slab has formed dangerous avalanche conditions could exist. Below 8,000 feet, where large grain facets and buried surface hoar continue to be reactive, the small soft slabs will likely be isolated to terrain features steeper than 35 degrees. Careful terrain management is essential as the snowpack continues to adjust to the new load.
