Three to five inches of new snow has fallen on a snowpack that is underlain by persistent weak layers that formed in November. Above 7500 feet, skiers or riders have the potential to trigger slab avalanches involving these old weaknesses. The possibility also exists to initiate loose snow sloughing or shallow pockets of wind slab in steep upper elevation terrain. Identify areas of concern for safe backcountry travel today. At low elevations, avalanches remain unlikely where less new snow has fallen on a shallow snow pack.
Slab avalanches up to 30 inches in depth could be triggered by a single person or by groups of skiers even after a slope has been tracked.
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.
