Since Saturday morning over four feet of snow, containing approximately 3.9 inches of snow water equivalency fell in the upper elevations of the Tetons and over two feet of snow and two inches of water fell at the lower elevations. Many natural avalanches have occurred of varying size over the last two days and although the snowfall has mostly ended, a possibility continues for natural avalanches to occur today at all elevations and on all aspects. Examples of reported natural activity includes slides on Mount Hunt, the Pyramid, Black Tail Butte and a west facing slope over the Teton Science School that impacted a parking lot. Skiers or riders who venture into steep avalanche terrain are likely to trigger slides involving recently formed slabs that have the potential to involve older snow layers. Yesterday, during High danger, a snowbaorder triggered a slide and was carried a long distance in the Mile Long Couloir in Granite Canyon. An inter-agency rescue effort, including GTNP Rangers, was able to remove the injured person who was not buried in the event. The rescue was challenging given the many slide paths that can impact the area during a big storm. Dangerous avalanche conditions exist and similar human triggered events could occur today. Cautious route finding and conservative decision making is essential today and recreationalists are urged to consider impacts to rescuers and friends as well as their own safety. The sensitivity of these unstable slabs may increase today in areas where they are loaded by west to northwest winds or in areas that may rapidly warm during periods of partial clearing.
Sustained snowfall and southwest winds have created wind slabs. These slabs lie upon sun crusts and faceted snow that formed during last weeks dry period. In steep terrain, wind slab depths could reach up to four feet at the higher elevations and up to two feet in depth at the lower elevations. These soft slabs will be very sensitive and are expected to run long distances.
Buried layers of faceted snow exist in the snowpack. Large to very large persistent slab avalanches could fail on these layers with depths from 3 to 5 feet at the higher elevations and 1 to 3 feet at the lower elevations. These dangerous slabs could fail naturally or be triggered by the weight of a single person or the release of a surface slab.
Periods of light to moderate snowfall are expected overnight. Accumulations of 2 to 4 inches are possible in the mountains. Valleys could receive an inch. Skies will be partly cloudy on Thursday with a slight chance of mountain snow showers. Temperatures are forecast to drop into the single digits below zero tonight. Daytime highs will rise into the positive single digits in the mountains and into the teens in the valleys. Northwest winds will remain light at 5 to 15 miles per hour and will veer towards the west and increase later in the day.Conditions are ripe for serious avalanche accidents. Large to very large slab avalanches could be triggered by humans on a variety of aspects at all elevations. These slabs could be two to five feet deep and may run long distances. In these conditions, especially in areas where the snowpack is shallow and has poor structure, snowpack stability assessment is difficult. The consequences of being caught in a large slab avalanche are likely to be severe. Monitor conditions. Direct sunlight, warming temperatures and any significant increase in winds could quickly elevate the avalanche hazard. The general avalanche hazard rating is forecast to be considerable in all areas and at elevations. It is important to realize that most recreational avalanche fatalities occur during periods of considerable to moderate hazard. Conservative terrain choices and excellent route finding skills are essential for safe travel in avalanche terrain.
