Two avalanche problems confront backcountry users today. First, small to large wind slabs could be easily triggered in steep, wind loaded terrain at the mid and upper elevations. Second, persistent deep slab avalanches remain a concern on a variety of aspects above 7,500 feet. These large to very large slab avalanches could be triggered directly by skiers and riders or indirectly from the release of a smaller wind slab. As the day progresses, continued snowfall and strong winds will increase the likelihood, depth and volume of both the wind slabs and persistent deep slabs. Loose snow sluffs will also be possible in very steep, upper elevation terrain that is not significantly wind affected. Monitor weather conditions, and utilize a conservative approach to terrain management. Avalanches below 7,500 feet are not expected today except for on small, isolated features.
Ridgetop winds picked up overnight and are expected to remain strong during the day. With ample snow available for transport along with steady snowfall throughout the day, wind slabs will continue to build. Skiers and riders could trigger these one to two feet slabs in steep, leeward terrain at the mid and upper elevations.
Since last Friday, around two inches of snow water equivalent has been added to weak, faceted snow that formed during the December drought period. Large triggers, such as snowmobiles, are more likely to be able to impact this deeply buried weak layer. However, the weight of a single person could cause failure of this weak layer if a shallow trigger point is encountered. These slabs could propagate long distances, have depths to five feet and are likely to carry severe consequences to anyone involved.
Light to moderate intensity snow showers will continue overnight before beginning to taper off during the day on Sunday as a ridge of high pressure begins to move into the region. Overnight lows in the mountains will remain in the low teens before rising into the low to mid 20s in the afternoon. Southwesterly to westerly ridgetop winds will range from 20 to 30 miles per hour.Strong ridgetop winds are expected to continue overnight, and daytime highs will be around 10 to 15 degrees warmer than Saturday. This scenario could lead to upside-down conditions. In the Tetons, where significantly more snow has fallen since Thursday, the general avalanche hazard is expected to be CONSIDERABLE above 9,000 feet. There, skiers and riders could easily trigger newly developed wind slabs one to two feet deep in steep, leeward terrain particularly near ridgelines.Between 7,500 and 9,000 feet in the Tetons and above 7,500 feet in the Togwotee Pass and Southwest Trails forecast zones, the hazard is expected to be MODERATE. In these areas, persistent deep slabs remain the primary concern. Large triggers, such as snowmobiles, are more likely to be able to impact the deeply buried December drought faceted layer. However, the weight of a single person could cause failure of this weak layer if a shallow trigger point is encountered. These dangerous slabs, which could be up to five feet in depth, could also step down from the release of a smaller wind slab. With the exception of small, isolated pockets of soft slab, avalanche activity is not expected below 7,500 feet.
