Yesterday, a skier triggered a small wind slab on a southeasterly aspect of peak 10,696 in Grand Teton National Park. Similar small to large surface slabs could be triggered by backcountry travelers in very steep, avalanche prone terrain at the mid and upper elevations. While becoming less likely, large to very large persistent slab avalanches remain a concern due to their high consequences. Don’t let previous tracks lull you into thinking a slope is safe; they are not an indicator of stability. Mostly stable snow exists at the lower elevations and avalanches are unlikely.
Skiers and riders still have some potential of triggering recently developed surface slabs up to two feet deep on very steep, avalanche prone slopes above 7,500 feet. Shallow pockets of new wind slab will slowly form throughout the day.
In steep terrain above 7,500 feet, some potential may remain for backcountry travelers to trigger persistent slab avalanches with depths of three to five feet. Large triggers, such as snowmobiles or the release of a surface slab, are more likely than an individual skier to initiate one of these slabs. Below 7,500 feet, skiers and riders might be able to trigger a persistent slab avalanche up to two feet deep on a very steep, isolated terrain feature.
The National Weather Service has issued a Winter Storm Warning beginning tonight at 6 PM. Snowfall intensity will increase overnight as a prolonged period of snowfall begins. Zonal flow aloft will develop, and southwesterly to westerly ridgetop winds will range from 20 to 35 miles per hour. Mountain temperatures will be fairly steady overnight before climbing into the mid-teens during the day.The general avalanche hazard is expected to be Moderate Sunday morning and steadily rise as the day progresses. Considerable hazard could develop during the day, particularly in the Tetons where accumulations will be highest. Throughout the day, skiers and riders will be increasingly likely to trigger newly formed wind slabs on steep, leeward slopes above 7,500 feet. These slabs could reach depths of one to two feet by Sunday evening. The likelihood of triggering large to very large persistent slab avalanches will also be on the rise as weight is added to the underlying weak layers of faceted snow. Monitor the weather and be willing to alter your travel plans if conditions warrant; or simply choose to stay in conservative terrain all day long.
