Yesterday, a snowmobiler triggered a large avalanche at 9,000 feet on a northeast slope. Today, similar events are likely. Above 7,500 feet, dangerous avalanche conditions could be encountered, and it is likely for skiers and riders to trigger large avalanches one to three feet deep on steep avalanche-prone slopes. Since these persistent layers lie beneath a thick slab of snow, it may be hard to detect the hazard without assessing the snowpack structure, and old tracks should not be trusted. At the lower elevations, there is only a few feet of snow, which has experienced above freezing temperature for over 24 hours, and avalanches are unlikely except for isolated pockets of deeper snowpack on steep slopes. This type of avalanche problem is best managed by terrain assessment and safe travel techniques of only exposing one person at a time. Evaluate steep slopes carefully and anticipate the potential consequences of triggering a large slab avalanche.
Since the end of an extended dry period on December 11th, in the Southwest Trails forecast area there was over three feet of snow with three inches of snow water equivalent. Beneath that snowfall, the snowpack consists of weak faceted snow and decomposing crusts. Persistent slabs are often at a tipping point, where the weight of a single person could tip the scales and trigger the avalanche.
( Discussion is generated from the previous day's afternoon forecast. )Dry weather will continue tomorrow with mostly clear skies and a valley inversion. In the mountains, temperatures are expected to start in the single digits and then warm into the twenties, while in the valleys temperatures should start below zero and then also warm into the twenties. Northwesterly winds are expected to be light at 10 to 20 miles per hour. In the Southwest Trails/Grey’s River and Teton forecast areas, the general avalanche hazard is expected to remain Considerable above 7,500 feet. In these areas, persistent slab avalanches are likely to be triggered by skiers and riders on steep avalanche-prone terrain. Buried weak layers vary in distribution and in some areas may be stubborn, but where this structure exists dangerous avalanche conditions could be encountered. These problem layers could be hard to detect without checking the snowpack structure. In the Continental Divide/Togwotee Pass forecast area, where there was less snowfall since December 11, the general avalanche hazard is expected to be Moderate. It remains possible for skiers and riders to trigger persistent slab avalanches one to two feet deep. In all the forecast areas, below 7,500 feet the general avalanche hazard is Low. At these lower elevations, there is only one to two feet of snow, which has experienced above freezing temperatures for over 24 hours, and avalanches are unlikely except for isolated pockets of deeper snowpack on steep slopes.
