Weak layers of faceted snow persist within the snowpack at the higher elevations and comprise the bulk of the snowpack in areas with a shallow snow cover. Yesterday a skier in the Snake River Range remotely triggered an 18 inch deep slab avalanche on a buried layer of surface hoar. Skiers in the Teton Range experienced a large collapse that failed on depth hoar. At the mid and upper elevations persistent weak layers may still be capable of failing due to the weight of a person. Slab failure may be more likely to be initiated on steep slopes by a larger triggers such as snowmachines and skiers or riders who hit a shallow weak spot in the snowpack. Avalanches are unlikely at the lower elevations except on isolated terrain features.
In steep terrain at the mid and upper elevations humans could trigger large slab avalanches one to three feet in depth. Avalanches are unlikely at the lower elevations.
Snow will develop and become steady by midnight. Moderate snowfall is expected to occur during the morning hours and gradually decrease during the afternoon hours. Winds will increase during this time and continue into Sunday night and Monday. After a brief break, snow will return late Sunday and continue through much of the day on Monday. Temperatures will be teens and 20s. Winds will be from the southwest and increase from 15 to 25 with gusts to 38 miles per hour. Sunday's system will favor the higher elevations and the Teton and Southwest Trails forecast areas. Several inches are possible by sunrise. Snowfall totals of 6 to 10 inches are likely in favored areas by sunset.New snow and moderate winds will begin to form new soft slabs on leeward aspects and will be increasing the load on buried persistent weak layers. In areas where new soft slabs begin to form on well-developed surface hoar they will quickly become sensitive to human triggers. Monitor conditions for increasing hazard. Carefully evaluate terrain features such as terrain traps, gullies and chutes that frequently avalanche and steep wind loaded avalanche starting zones. Pockets of new slab could grow to depths of 6 to 18 during the day. Deeper instabilities persist and present the potential for deeper slab avalanches, one to three feet deep, to be human triggered on steep slopes above an elevation of 7,500 feet. The general avalanche hazard is expected to be moderate but increasing above that elevation. The general avalanche hazard below that elevation is expected to be low and also will be on the increase.
