Snow and increasing winds will form new soft slabs on leeward aspects and will be increasing the load on buried persistent weak layers. In areas where new soft slabs begin to form on well-developed surface hoar they will quickly become sensitive to human triggers. Monitor conditions for increasing hazard. Carefully evaluate terrain features such as terrain traps, gullies and chutes that frequently avalanche and steep wind loaded avalanche starting zones. Deeper instabilities persist and present the potential for deeper persistent slab avalanches to be triggered by humans or the release of a wind slab. Loose snow sloughs are likely to release from cliff areas, steep road cuts and steep hanging snowfields. Winds are forecast to strengthen and will be increasing the hazard at all elevations as the day progresses. Grand Teton National Park has closed the north end of the Moose-Wilson Road to motor vehicles at its junction with the Murie Ranch Road. Visitors may still walk, ski or snowshoe on this section of the road. This closure will remain in place for the duration of the partial government shutdown.
Increasing southwest winds will be forming new soft slabs on weak old snow surfaces. These new slabs are expected to grow to depths of 6 to 18 inches during the day and are expected to become very sensitive to human triggers.
New snow and wind will be increasing the load on persistent weak layers of faceted snow that are buried within the snowpack. Some potential exist for large slab avalanches involving older snow layers to be triggered by the weight of a person, snowmachine or the release of a soft wind slab. These older slab avalanches could be up to three feet deep.
After a brief lull, another more impactful storm will move into the area. Snowfall will increase after midnight and become heavy from around 2AM to 11AM. This system will bring another 6 to 12 inches of snow to the region. It will be accompanied by steadily increasing southwest to west winds. On Monday winds will frequently gust to 50 to 60 miles per hour along the high ridges throughout the daylight hours. Valley winds will steadily increase to sustained speeds of 20 with gusts to 30 miles per hour from sunrise into the afternoon. The snowfall and winds are forecast to decrease around sunset. Temperatures will be in the teens in the mountains and in the upper teens to upper 20s in the valleys. There were two avalanche fatalities in the Rocky Mountain region yesterday. A snowmobiler died west of Choteau, Montana and a backcountry skier died near Red Mountain Pass in southwest Colorado.Very strong sustained winds and new snow will create dangerous avalanche conditions at all elevations in all of our forecast areas. Blowing and drifting snow will cause whiteout conditions and rapidly load a snowpack with poor snow structure and persistent weak layers. Natural avalanche activity is likely on a variety of aspects at all elevations. Large slab avalanches are likely and very large slab avalanches are possible. The Wyoming Department of Transportation will close the highway over Teton Pass at 3AM for the purpose of conducting avalanche hazard mitigation efforts. Avalanches may impact highways on that road and in the river canyons during this storm. On Monday the general avalanche hazard is expected to high in the Teton and Greys River/Southwest Trails areas. Travel in avalanche terrain is not recommended. Large to very large natural avalanches are likely. The general avalanche hazard is expected to be considerable in the Togwotee Pass area where conditions will also be dangerous. Large human triggered avalanches are likely and large natural avalanches are possible. Expert terrain analysis skills are essential for safe travel in this area.
