Tetons

Triggering an avalanche in steep, rocky terrain remains possible today. Sheltered and shady slopes at the upper elevations that held snow prior to November 2 are of primary concern. You can use your shovel to dig down in the snowpack and see if this obvious gray line exists near the ground. Remember that it is early season out there and any avalanche involvement could result in traumatic injury.

Well the skies finally parted yesterday afternoon/evening, and no new observations of avalanches were reported. Grand Targhee Ski Patrol performed avalanche hazard mitigation routes at the ski area and results were few and far between, with none reaching down to the November 2 layer. Perhaps the cold temperatures helped in seizing up any avalanche activity. Triggering an avalanche on this layer is becoming less likely, but high elevation terrain in steep and rocky areas is still suspect. These are the areas where poor snowpack structure is mostly likely to exist. You can always dig a quick pit and perform an extended column test on safe slopes that are representative of the ones you plan to ski or ride. 

The November 2 layer remains the primary concern for avalanches large enough to bury a person. That layer is now buried by 2-4 feet of snow at the middle and upper elevations. Much of this slab is composed of stiff snow. Human triggered avalanches were observed on this layer on November 5 at Grand Targhee, and explosive triggered avalanches involving this layer were observed at JHMR on November 9. Natural activity on this layer has been curiously quiet throughout this major storm cycle, but observations have been limited due to conditions. Since November 4, around 5 inches of snow water equivalent has fallen on this layer at the upper elevations.  

Major Snow and Uncertainty

The Tetons picked up snow every day from November 2 to November 11. To top it off, orographic convection really kicked in on November 10 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. No activity has been observed on this suspect interface since November 9, but there is still some uncertainty around its reactivity in high, rocky terrain.

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.