Very strong winds and approximately three feet of snow received over the last four days have resulted in dangerous avalanche conditions at the upper elevations where wind slabs could be easily triggered in steep terrain and a chance also continues for larger avalanches, involving older persistent weak layers, to occur. Natural avalanche activity is also possible today on high exposed terrain, especially as winds veer to the northwest this afternoon. Although less sensitive and smaller in size, backcountry riders and skiers could trigger similar events at the mid elevations. Cautious route finding is essential and an evaluation of the snowpack in steep terrain is advised. Avalanches remain unlikely at the low elevations except for the possibility of small isolated events on very steep features.
Winds from the south to northwest have created sensitive soft slabs. Riders and skiers have the potential to trigger these slabs at the mid and upper elevations although they will be most sensitive and larger along high elevation ridge crests and areas prone to wind loading. These slabs could have depths to three feet.
Weak snow that formed during a prolonged dry period and was buried on December 5th remains a layer of concern in terrain above 8500 feet. Although avalanches involving this layer are likely to require a larger trigger such as a moving wind slab or a snowmachine, failure could still occur to the weight of a single person if a particularly weak spot on a slope is impacted.
This evening, an Arctic cold front will push through western Wyoming and bring with it a brief period of snow and high wind, which will shift to the northwest, as the front passes. Only an inch or two of snow will arrive with the front but temperatures behind it will drop significantly. Expect highs in the mountains tomorrow to struggle to reach single negative digits after overnight lows of -10 to -15. Frigid temperatures and very little, if any, wind loading are expected tomorrow. These factors will make natural avalanches trend towards unlikely in the Tetons and Togwotee Pass and so reduce the overall avalanche hazard in those areas to Moderate. The Grey’s River area appears to have a potentially more active weak layer, which has received the same or greater stress from recent storm snow and wind loading. Though we do not have strong confidence that natural avalanches will occur there, the increased thickness of slabs there, which could be up to five feet thick, and the potential to trigger these from a distance or from below shouldn’t be ignored. These factors result in a Considerable danger rating at upper elevations, on steep and wind loaded slopes above 8500 feet in that zone.
