Heavy snowfall into the afternoon and accompanying strong winds will rapidly elevate the avalanche danger. New wind slabs are forming and will increase in size and sensitivity at the mid and high elevations. Persistent slab avalanches on weak faceted snow will be a problem at all elevations. New snow is falling directly on a snowpack with poor structure at low elevations and adding load to buried weaknesses at higher elevations. Avalanche conditions will become more dangerous as the day progresses and conservative decision making is necessary for safe backcountry travel.
New snow and strong west winds are expected to rapidly form wind slabs on the snow surface this morning. These slabs are forming on crusts, surface hoar and faceted snow and given the predicted rapid loading are expected to be very sensitive with depths increasing to one foot later in the day.
At the mid and upper elevations slab avalanches lying on weak faceted snow that was buried at Thanksgiving could fail to depths of three feet. These slabs could be triggered by backcountry travelers, by the initiation of a surface slabs or possibly release naturally if enough new snow loading occurs. At the lower elevations, new snow is falling on a weak shallow snowpack entirely comprised of faceted snow and slabs to one foot could be triggered this afternoon in steep terrain features where wind loading occurs. The size and sensitivity of these persistent slab problems will increase as the storm rapidly loads slopes.
( Discussion is generated from the previous day's afternoon forecast. )The National Weather Service has issued a Winter Storm Warning for the Teton and Gros Ventre ranges from 11pm tonight through 5pm Wednesday and Winter Weather Advisories for other parts of western Wyoming. The storm that is to bring snow to the area by midnight is to bring significant accumulations and be accompanied by strong west winds. Accumulations of over a foot of snow are expected in the higher elevations of the Tetons with accumulations of just under a foot in the other forecast areas. Summits winds are to have twenty to twenty-five mile per hour averages with gusts to near forty. Low elevations are to receive much less snow however winds could cause blowing and drifting snow and white out conditions. Temperatures are to rise from the low to upper teens in the mountains while valleys reach the upper twenties. The general avalanche danger will increase to Considerable above 7500 feet. At those elevations, new sensitive wind slabs will form in steep leeward terrain and increase in size and sensitivity as the day progresses. The potential for avalanches involving the older weaknesses within the snowpack will also increase. These larger avalanches, that could have depths to three feet, may be triggered by backcountry travelers, by triggered surface slabs, or naturally if excessive loading occurs by the storms end which is to be later tomorrow afternoon. Below 7500 feet, the danger is to increase to Moderate as the new snow will be very sensitive in specific steep terrain features where it is wind loaded on a generally shallow and faceted snowpack.
