Rapid loading is occurring and dangerous avalanche conditions are developing this morning. The National Weather Service has issued a Winter Storm Warning through 9 PM tonight, and temperatures are starting out 10 to 15 degrees warmer than yesterday morning. As the day progresses, the chance for backcountry travelers to trigger newly developed wind slabs will be on the rise at the mid and upper elevations. Up there, the likelihood of triggering large persistent slab avalanches will also increase throughout the day. These deeper slabs could step down from the release of a wind slab. Natural activity will also become possible. Conservative terrain choices will be essential for safe travel in the backcountry. At the lower elevations, the possibility of triggering shallow pockets of soft slab could develop.
New snowfall, ample snow available for transport and strong southwesterly ridgetop winds have combined to build wind slabs in leeward terrain. These slabs are forming on dry settled powder, surface hoar and sun crusts. Skiers and riders venturing into steep, wind loaded terrain could easily trigger these slabs with depths up to 18 inches by this evening.
Layers of weak, faceted snow exist in the snowpack. The chance for backcountry travelers to trigger persistent slab avalanches will be on the rise as load is added onto these weak layers. By the end of the day, these slabs could reach depths of two to four feet.
Snowfall will decrease overnight as the moisture associated with this weather system moves away from the area. Temperatures will be near or below zero by morning. Skies will be clearing on Monday with lingering snow showers and areas of blowing snow during the early morning hours. Temperatures will rise into the single digits above zero in the mountains and into the upper single digits and low teens in the valleys. Winds will be northerly and subside to speeds of 10 to 20 miles per hour.The general avalanche hazard is expected to be considerable at the mid and upper elevations of the Teton area. Slab avalanches formed by west-southwest to west-northwest winds are likely to be triggered by humans who venture into steep wind loaded avalanche starting zones and terrain features. These slabs could be up to two feet in depth and could step down to depths of three feet if they fail on persistent weak layers of faceted snow that formed earlier in the season. These slab avalanches could be some of the largest of the season and may have severe consequences. Conservative terrain choices are essential for safe travel in avalanche terrain. Lesser amounts of snow have fallen so far in the Togwotee Pass and Greys River areas. In these areas and at the lower elevations of the Teton area the general avalanche hazard is expected to be moderate. In these areas small to large slab avalanches one to three feet in depth could be human triggered in steep wind loaded avalanche stating zones and terrain features. A careful evaluation of the snowpack and terrain is necessary for safe travel in avalanche terrain.
