Tetons

Triggering an avalanche in steep, rocky terrain remains possible today. Slopes that held snow prior to November 2 and recieved wind loading during the most recent storm cycle are of primary concern. You can use your shovel to dig down in the snowpack and see if this obvious grey line exists near the ground. 

Remember that it is early season out there; a high degree of uncertainty in snowpack structure exists and traumatic injury is possible with any avalanche involvement.

Grand Targhee is closed to uphill traffic due to explosive mitigation efforts today. They will reopen to uphill traffic this weekend.

The layer of weak faceted snow was formed from October 28- November 2 and is now buried by 2-4 feet of snow at the middle and upper elevations. Much of this slab is composed of stiff snow and in some aspects, wind drifted snow. The weak layer is most prevalent at the upper elevations and on northerly aspects at the middle elevations, but a good amount of spatial variability exists.  Since November 4, around 5 inches of snow water equivalent has fallen on this layer at the upper elevations.  

Yesterday's snowfall was low density with little wind, but places like Grand Targhee still managed to pick up another 0.5 inches of snow water equivalent. This is a lot of water in a very short period of time and a lot of stress on a young snowpack. 

Major Snow and Uncertainty

The Tetons have picked up snow every day since November 2. To top it off, orographic convection really kicked in yesterday with favored locations picking up well over a foot of low density snow. In this time period around 5 inches of snow water equivalent has accumulated at the upper elevations. Ridge top winds have averaged from west to south and have been moderately strong but have tapered significantly. All of this snow (and even a little rain) has fallen on weak snow and crusts that were formed from October 28-November 2. During the beginning of the cycle human triggered avalanches were observed at Grand Targhee. Widepread collapsing and cracking were observed on this layer throughout the storm cycle on Teton Pass, as well as avalanches within the new snow and its various density changes. Explosive triggered avalanches were observed at JHMR, with some likely reaching down to the November 2 layer. What will we see when the skies part?

The lack of natural activity on the November 2 layer throughout the barrage of storms has been curious, but maybe this is just due to a lack of observations. This layer is mostly composed of 1-2 mm facets with a few larger ones thrown in for good measure. It could possibly contain preserved surface hoar in some protected locations, but this seems unlikely after 5 inches of water has been dumped on it. Some extended column tests are still propagating on this layer, but scores seem to be going up.

Stormy skies have made observations tough. Cold temperatures and clear skies should give us a better window into the patterns of instability.