The Bottom Line: At upper elevations, avalanches may be deep and unsurvivable. Dangerous conditions exist after another significant storm has added more snow over a very weak layer. Stay off of, and out from underneath slopes steeper than 30 degrees if you see signs of danger like recent avalanches, and shooting cracks.
Snow and Avalanche Discussion
When digging around for information today, the most common response was "I thought about going out, but the snow quality seemed low." We are in the dark regarding what happened during the storm. We do know that we picked up anywhere from 0.3†to 1.2†of water equivalent, with the Salmon la Sac being the winner. Conditions are likely very dangerous in that area, and as one goes up in elevation.
Mission Ridge and Blewett Pass only picked up a few inches of new snow. A freezing rain crust formed up to about 4500ft across the eastern slopes, with a rain crust likely up to at least 6,000ft. Above 6,000ft the new snow is likely sitting on a recent crop of surface hoar and/or facets, which could make for poor bonding and potentially wide avalanches.
Avalanche Problems
Persistent Slabs
On the 31st, I found a highly reactive layer of buried surface hoar down about 18” near Leavenworth. The instability on this layer was found starting at 5,600ft and became ‘in your face’ at 6,400ft. Here, I triggered a number of very wide avalanches while walking on a ridgeline from a distance. A recent avalanche cycle on this layer was observed, but not everything had slid. Activity appeared to be mainly on North through Southeast aspects. These avalanches were surprising in how widely they broke across a slope and the fact that they were triggered from up to 200ft away. Observers in the Washington Pass area also were triggering avalanches on this layer the previous day. On Rock Mountain near Stevens Pass, a very wide crown speaks to the presence of a layer of buried surface hoar. I would be wary of any steep, open slopes above 6,000ft right now, because I would expect these persistent grains to be buried 2 to 3 feet down. From recent experience we know that slides on this layer can be very wide. Snowpack tests can help identify this layer, but cannot prove its absence. Be observant of shooting cracks or collapsing to check for this layer. Use slopes of less than 30 degrees for travel, and avoid getting underneath any steep slopes at upper elevations. At lower elevations, where water has percolated through the snowpack and refrozen to create thick crusts the snowpack is likely bonded much better.
The further east you get, the less snow is on the ground. Recent observations from Mission Ridge and above Mazama the a speak to a shallow snowpack with weak snow near the ground. This poor snowpack structure warrants respect, because if the layer near the ground failed, the avalanche could be well over 4 feet deep. Places to be cautious of in particular are where stiff slabs sit over weak snow, slopes where the ground and rocks may be showing with deep drifts nearby, and any steep slopes on the far eastern side of the range.
