Signs of deep instability on Schallenberger Ridge

We toured on the northerly aspects of Schallenberger Ridge today. Our goal was to look at potential deep instability following data from Trestle Peak and Cold Stream Canyon indicating potential weakness at the Feb 21 old/new snow interface and assess wind slabs along the way. Winds were strong up to about 12:30 pm and seemed to decrease a bit and become less gusty following the cold front passage. Snowfall rates also peaked during the cold front passage with a rate of S10 observed around noon. After that, snowfall rates decreased to around S2 to S5.

Moderate amounts of drifting snow was observed along the ridgetop cornice areas this morning, prior to the onset of higher intensity snowfall. The newest round of wind slabs in this area were up to 1 foot thick and showed minimal propagation in the morning with propagation increasing slightly in the early afternoon. Wind slabs were anywhere from 4F hard to 1F hard with F hard storm snow below.

We choose a spot just far enough below the ridgetop to be out of the wind loading zone for our snowpit (NW aspect, 6,970', NTL terrain). Stepping off of skis to dig the pit, boot penetration down into the snowpack triggered a snowpack collapse with an audible whumpf. It did not feel as though the entire slope collapsed, but it did radiate out at least 20 feet. Digging down into the snowpack we found a crust with some minor faceting below it at the Feb 21 old/new snow interface. We also identified a layer of graupel and the Jan 29 surface hoar layer further down. Snowpit tests indicated that the Feb 21 layer was most likely the layer that collapsed and produced the whumpf. While the Feb 21 layer is not alarmingly weak, it is currently receiving rapid loading of substantial SWE, creating concerns for possible deep instability.