Strong winds and heavy snowfall will create very dangerous avalanche conditions at the mid and upper elevations. Very large slab avalanches may release naturally or be triggered by humans. These dangerous avalanches could run long distances. Travel in avalanche terrain is not recommended during periods of high hazard. The hazard will be on the increase at the lower elevations where new wind slabs will begin to form on steep slopes and some potential exist for large avalanches to impact lower elevation run out zones.
At the mid and upper elevations, strong west to southwest winds will be increasing the load on persistent weak layers that have a proven history of producing large avalanches. Avalanche activity is likely today on steep slopes. These slides could be 3 to 5 feet deep. They may release naturally or be human triggered.
New soft slabs will begin to form on leeward aspects. These slabs could grow to depths of two feet by the end of the day at the higher elevations and to depths of 6 to 18 inches at the mid and lower elevations. These fresh slabs could be human triggered on steep slopes and could step down to deeply buried layers of faceted snow at the upper elevations and on northeast through northwest aspects at the mid elevations.
Pacific moisture will continue to stream into the region. Pulses of moderate to heavy snowfall will continue to occur during the next 24 hours. This flow will continue to favor the Teton Range and the southern portion of our forecast region. Additional snowfall of 10 to 20 inches are possible in the Tetons by midnight tomorrow. Another foot is possible in the other ranges. Valley locations should get another 5 to 8 inches. Conditions will remain mild for mid-December but cooler. Temperatures will be in the teens and 20’s in the mountains and in the 20’s to near 30 in the valleys. West to southwest winds will continue to be strong at 20 to 35 with gusts from 50 to 60 miles per hour along exposed ridge crest during the morning hours on Friday.Persistent weak layers near the base of the snowpack at the mid and upper elevations continue to pose a very significant hazard. Very large avalanches could release naturally or be triggered by the weight of a single person on these problem layers. Large and dangerous slab avalanches could be triggered on these weak layers after a slope has been crossed multiple times by a skier or rider and remotely from flat terrain below or above a steep slope due to the weight of a single person. Travel in avalanche terrain during these conditions requires expert terrain evaluation skills and conservative terrain choices. Strong winds are also forming dense new wind slabs that can be triggered by humans who venture into steep wind loaded avalanche starting zones. At the mid and upper elevations these surface slabs could initiate a deep slab avalanche on the persistent weak layers at the base of the snowpack. The general avalanche hazard rating at the mid and upper elevations will be dependent of the amount of new snow and is expected to be considerable or high. The hazard at the lower elevations is expected to be moderate.
