Areas of unstable snow exist and human triggered avalanches are possible. Yesterday in Grand Teton National Park, at an elevation of 12,238 feet the second skier on a slope was caught but not injured after triggering a hard slab avalanche on a very steep northerly aspect. A snowmobiler on Togwotee Pass was buried in an avalanche yesterday afternoon and did not survive. Humans who venture into very steep avalanche starting zones could trigger dense winds slabs. Very large deep persistent slab avalanches may still be a concern in isolated areas, especially for larger triggers like snowmachines. Avalanches are unlikely at the lower elevations except on isolated terrain features during the warmest portion of the day. As the day progresses, sunshine and warming temperatures could increase the sensitivity of areas of unstable snow to human triggers at all elevations. Conduct snow stability assessments, monitor conditions and avoid steep terrain in areas where the snow structure is poor.
Dense wind slabs could be triggered by skiers and riders in very steep, avalanche prone terrain above an elevation of 7,500 feet. These slabs, with depths of one to three feet, could become more susceptible to human triggers as the day warms.
In isolated areas, the weight of a single person may be sufficient to trigger a deep persistent slab avalanche if a shallow, weak zone is encountered. Large triggers, such as snowmobiles, the release of a wind slab or a cornice failure, are more likely to trigger one of these deadly avalanches. Slab depths could vary from four to eight feet at the higher elevations and two to four feet at the lower elevations.
Pacific moisture will begin to stream over the forecast area tonight. Snow showers will develop and could bring 2 to 4 inches of new snow to the mountains overnight. Snow chances will decrease on Wednesday morning, before increasing again by noon. This increase will infiltrate from south to north through the afternoon and into the evening. An additional 4 to 8 inches is expected by Thursday morning with locally higher amounts possible in the highest favored terrain. Conditions will be milder. Temperatures will be in the teens tonight and rise into the 20s and 30s during the day. Snow may mix with rain as the freezing level rises to 6,000 to 7,000 feet. Winds will be from the south-southwest at 10 to 15 miles per hour with higher gusts.Very large deep persistent slabs avalanches could be human triggered on very steep avalanche prone slopes in areas with poor snow structure. These dangerous slabs could be 4 to 8 feet deep. Larger triggers like snowmachines and cornice drops are more likely to trigger one of these dangerous slabs. Previous tracks may not be an indication of stability. Pockets of older wind slab and small pockets of new wind slab could also be triggered by humans in very steep terrain at the higher elevations. The general avalanche hazard is forecast to be moderate. A careful evaluation of the snow structure and conservative terrain choices are warranted in areas which exhibit poor snow structure.
