Wind Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1–2
The latest storm cycle which started on Monday and continued into early Wednesday morning brought over a foot of snow to the Southern Wallowas and Blues and about half that amount for the Northern Wallowas and Elkhorn mountains over the same time period. This new snow was accompanied by winds from the southwest, west, and northwest, and slightly rising temperatures. The new snow, coupled with the moderate (stronger at some locations) westerly winds, has created windslabs on leeward northeast, east, and southeast facing terrain at all elevations. This new load of snow is poorly bonded to the older snow it rests upon. The reason for the poor bond at the new snow/old snow interface is the presence of surface hoar and near surface facets on the old snow surface. These now buried persistent weak grain types that the new snow rests upon will inhibit the bonding process at the new snow/old snow interface resulting in unstable windslabs. Yesterday, while ski touring in the Northern Elkhorns, I observed wind deposited snow and windslab formation on all the east and northeast slopes I traveled upon from trailhead to ridge top. While ascending a northeast facing ridge near the Anthony Lakes ski area I heard several collapses or "whumpfs" just above 8000' . I also observed instability in my snow pits. My Snowpit columns were failing with an easy amount of force at the new snow/old snow interface accompanied by propagation. Propagation occurred on a snow pit that was dug at about 8400' . At this location the new snow ( windslab ) was about 10" thick. I also did many ski cuts on small, steep, terrain features but was unable to trigger any avalanche activity. That said, because of other red flags I observed on my ski tour I chose to descend on safe slopes less than 30 degrees steep. Even though I did not observe avalanche activity, I believe that today we are in a period of heightened avalanche danger. I also think human triggered avalanches are possible on steep, leeward facing terrain near and above treeline. If you choose to recreate on terrain steeper than 30 degrees today, evaluate the slope very carefully before proceeding. If you observe hollow sounding/feeling snow, collapses, whumpfs, or shooting cracks, these are red flags that are warning you that the slopes you are traveling upon are unstable and could avalanche.
(12/21/2022)
Extended Column test performed on a northeast facing slope in the Northern Elkhorns on Wednesday, 12/21/22. Elevation was 8452 ' and the slope angle was 32 degrees. Column failed easily, full propagation, down about 10" from the snow surface. The 10" of new snow at the surface is windslab. The weak layer was about a 1" thick layer of buried surface hoar. The sliding surface just below the surface hoar was 1 finger hard old snow that fell about 10 days ago. Height of snow at this location is 185 centimeters or about 6' .
