Tetons

Last night’s intense snowfall has created very dangerous avalanche conditions at the mid and upper elevations. Conditions are now ripe for a serious avalanche accident. On Thursday a skier triggered a small slab avalanche in Thanksgiving Bowl. On Friday another skier triggered a larger slab avalanche in Thanksgiving Bowl. Natural avalanche activity likely occurred in the backcountry overnight and is possible today. Large avalanches are failing on persistent weak layers that have been deeply buried. These conditions are especially dangerous because a person may ski or ride multiple steep slopes and then unexpectedly trigger a very large slab avalanche. The best way to manage today’s hazards is stay off of and out from under steep slopes with a suspect snow structure. Expert terrain evaluation and route selection skills are essential. For these reasons backcountry users are encouraged to stay on low angle slopes and avoid avalanche terrain in suspect areas. Avalanches are unlikely in areas at the mid and lower elevations where the new snow that has fallen since last Sunday has accumulated on bare ground.

Temperature inversions may develop under a transient ridge. Skies are likely to be clear, however some areas of low-level status clouds and valley fog are possible. Skies will be mostly sunny in the morning with increasing clouds in the afternoon. Areas of light snowfall are possible Sunday evening. Temperatures are forecast to drop below zero overnight and rise into the 20s during the day. Winds will be light at 15 miles per hour with higher gusts and will back from the west to the south.Conditions will continue to be dangerous on steep slopes above an elevation of 8,500 feet. Large slab avalanches could be triggered by humans on persistent weak layers that formed on old snow surfaces during an extended dry period in November. Persistent weak layers are problematic because large slab avalanches can be triggered on them by the weight of a single person even though a slope has been previously crossed. These slides can also propagate long distances, be triggered from below, occur in treed areas and occur on slopes that rarely slide. These slides could be 2 to 4 feet deep. The general avalanche hazard is expected to considerable on all aspects above an elevation of 9,000 feet and on steep slopes that face north down to an elevation of 8,000 feet. Avalanches are unlikely below an elevation of 8,000 feet and on solar aspects up to an elevation of 9,000 feet. Excellent terrain evaluation skills, a knowledge of the extent and distribution of persistent weak layers and conservative terrain choices are essential for safe travel in avalanche terrain.