Layers of persistent weak snow lie hidden within the snowpack. These weaknesses were buried as long ago as December 11th and as recently as January 12th. Slab avalanches involving these layers could be human triggered today in steep avalanche terrain above 7500 feet where they could be small to very large in size. Below that elevation, activity is limited to very steep isolated terrain features. Caution is advised as these are dangerous conditions and slab avalanches could occur even after a slope has been tracked. Snowpack evaluation is recommended to understand where these persistent weak layers still pose a threat.
Skiers and riders have the potential to trigger slab avalanches involving faceted snow and surface hoar. Above 7500 feet, depending on the layer initiated, they could be soft or hard and have depths of two to five feet. At low elevations, where the snowpack is comprised mostly of sugary snow, slab depths of one to two feet are possible in isolated areas.
( Discussion is generated from the previous day's afternoon forecast. )High pressure will return tonight and inversion conditions are to develop by morning. Temperatures will start below zero in the valleys and in the single digits up high. By mid-afternoon, highs should reach the low twenties at all elevations. Winds are to be light to moderate from the northeast. The avalanche danger above 7500 feet will be Considerable in the Southwest Trails area and Moderate in the Teton and Togwotee Pass areas. Persistent weak layers lie within the snowpack. These layers lie under the past week’s snow and can also be found deeper in the snowpack, at varying depths including near the ground. The deeper layers are becoming less likely to fail, but if triggered could cause very large hard slab avalanches with depths to five feet. The presence of weak snow and therefore the likelihood of triggering slides is greatest in the Southwest Trails area. Below 7500 feet, the weak layers have generally combined, resulting in a snowpack with poor structure. In isolated areas, small slabs could still be triggered in very steep terrain.
