Dangerous avalanche conditions exist in the backcountry. Significant snowfall and strong southwest to west winds since early Tuesday morning have formed sensitive wind slabs at all elevations. These slabs will be larger and more sensitive at the upper portion of the mid elevations and at the upper elevations where the possibility also exists for the release of very large and destructive hard slabs that lie on a layer of weak faceted snow near the base of the snowpack. Predicting the release of a persistent slab is difficult and requires an evaluation of the snowpack to the ground and the best way to avoid an accident today is by simply making conservative route and terrain choices. Remember to consider the terrain above your route as it is possible for avalanches to run long distances today. At the low elevations, smaller avalanches could be triggered on very steep terrain features and terrain traps should be avoided.
New wind slabs have formed on leeward terrain. These slabs will be sensitive to backcountry riders and skiers today and could release naturally. These slabs will release as soft slabs and could have depths to three feet at the high elevations, two feet at the mid elevations and eighteen inches at the low elevations.
Rapid loading has increased the likelihood for the release of large to very large avalanches involving weak snow buried on December 5th. Such an event could be triggered when a single person hits a weak spot on a slope, by larger triggers such as groups or a snowmachine, or by the release of a wind slab. If triggered these slabs will be hard, have depths of three to seven feet and are likely to have dire consequences for anyone involved.
A Winter Storm Warning issued by the NWS is current and will remain in effect until 11pm tomorrow night. Light to moderate snowfall will continue overnight. Expect snowfall to increase in intensity in the early morning hours. Snow will be heavy at times. In the Tetons expect 5” of new snow by morning and 20” by the end of the day. The Southwest Trails area can expect 6-8” by morning and 20” at days end. The Togwotee Pass/Continental Divide area will see 3-5” by morning and 12” by the evening. Wind speeds overnight will average in the teens and be out of the west. Winds will increase into the 25-30 mph range during the day tomorrow out of the west. Temperatures will rise into the mid twenties in the upper elevations and into the low thirties in the low elevations.The general trend for tomorrow will be an increase in avalanche danger in all forecast areas. Travel in avalanche terrain will not be recommended in many areas. Expect natural activity to be likely in the upper elevations. The danger will be high in the upper elevations of the Teton, Togwotee and Southwest Trails forecast areas. The danger will be in the considerable to high range in the mid elevations of the Tetons. Expect the danger to be considerable in the lower elevations of the Tetons and Southwest Trails and moderate on Togwotee. A variety of potential weak interfaces will allow the possibility of a wide range of avalanche sizes. The potential for large, destructive and un-survivable avalanches will be real tomorrow.
