The chance continues for skiers and riders to trigger slab avalanches in steep terrain at the mid and high elevations. Generally, two persistent weak snow layers lie in the snowpack. Avalanche events are most likely to involve wind formed slabs that lie over surface hoar and facets that were buried last week or could potentially involve a widespread weakness that was buried in late November. Identify features of concern and evaluate the snowpack prior to entering steep avalanche terrain. Avalanches are unlikely at the lower elevations except on isolated terrain features.
In steep wind loaded terrain, slabs formed last Wednesday and Thursday could be triggered to depths of sixteen inches by a single person. The slight chance also continues for deeper slabs to depths of three feet to be triggered by larger forces such as groups of people, snow machines or moving snow initiated higher in the snowpack.
A winter weather advisory has been issued by the National Weather Service for the Teton and Gros Ventre Mountains. The incoming storm is to bring significant snowfall tonight and into Wednesday. The storm is start on the warmer side for this time of year and cool through the night. Winds will be a significant factor with this storm event. West wind average speeds are to increase into the forties with gusts in the sixties. By sunrise nearly a foot of snow is predicted in the higher elevations, especially in the Tetons, while valleys are to see two to six inches. Winds are to be on the decrease during the day but are likely to be a challenge to visibility during the morning. Temperatures near twenty degrees are expected on Wednesday. The general avalanche hazard is expected to increase to Considerable above 7500 and to Moderate below that elevation. New wind slabs will quickly form on a variety of snow surfaces overnight. Given the rapid loading, these slabs will be sensitive to skiers and riders in steep leeward avalanche terrain. If the storm produces as expected, these new slabs could have depths to over two feet at the higher elevations and to depths of a foot at lower elevations. The existing persistent slab problems will also become more likely to trigger as they are stressed by the new snow load creating the possibility for large avalanches. Below 7500 feet, strong winds will form pockets of new surface slabs in very steep terrain. These slabs will form on a snowpack with poor structure, particularly on north aspects. Conservative decision making is essential to manage these dangerous avalanche conditions.
