Observation: Public

Observation Details

Observed Avalanches

Signs of Unstable Snow

Observations

Avalanche activity was observed as we exited Thunder Basin around 2:30/3pm after a snowier-than-expected but otherwise eventless morning in the Slot Couloir on Snoqualmie Mountain. As we skinned up and out of Thunder basin towards the col on Snoqualamie's western ridgeline, we saw numerous but very small natural soft slabs that had very recently pulled out below the large cliffs on Snoqualmie Mountain west of the Slot/Snot. These were appx 10-30ft wide, crowns of 2-4 inches, running 100-200ft down the N/NW aspect of the basin. Due to low visibility, we did not see these until we were basically on top of them -- many had come down over and covering the skin track, which we know had been traveled in the past few hours. We were close enough to the exit, with minimal overhead hazard, so we chose to continue on. It was clear to us that these small slabs were the result of ongoing loading from winds cresting the ridge and from very visible spindrifts depositing new snow at the base of cliffs, which were consistently shedding snow. While near the top of the chute's bootpack two smaller surface slides (10-15ft wide, 2-3 inch crowns) came down from pockets left and right of the exit bootpack -- one of which slid into a group member. Luckily the slide was small enough that she was able to stay on her feet, but scary enough in the poor viz and windy conditions. Knowing we were within ~20 feet of the ridgeline and that very little unstable snow was left above us, we chose to move quickly and get to the ridgeline and out of this increasingly wind-loaded area.

Some good lessons were learned. That afternoon's (or perhaps just that specific terrain feature's) unexpectedly strong winds and the ~2 inches of snow that fell throughout the day (vs. a forecast which called for no accumulation) caught us off-guard -- A good reminder to keep an eye on changing weather and have a backup exit route planned to accommodate changing conditions. And, while our particular route was fairly low-consequence given the small size and surface-level nature of the unstable snow, in more exposed terrain or with greater overhead hazard, even these small slides could have had much more serious consequences.