A widespread natural avalanche cycle occurred during the big storm at the end of December/beginning on November. The snowpack is just beginning to adjust to this load and will take some time to do so. Triggering avalanches that fail on the faceted snow from the mid-November drought will be a possibility for some time.
Mostly clear and cold. Calm to light winds blowing out of the W. Mostly sunny where we were, though icy clouds were hanging over the Smokys and Pioneers at times.
# | Date | Location | Size | Type | Bed Sfc | Depth | Trigger | Photos | Details |
---|---|---|---|---|---|---|---|---|---|
3 |
Dec 1, 2022 (+/- 1 day) |
McDonald Peak E 9400ft |
D2 | SS-Soft Slab | N-Natural | Report | |||
1 |
Dec 1, 2022 (+/- 1 day) |
Imogene NE 9700ft |
D2.5 | HS-Hard Slab | N-Natural | Report |
Ben drove up to Petit and back before the tour and observed countless avalanches that failed during the storm. Most of these had failed during the storm and crowns, bed surfaces, and debris had been partially obscured in most places. In alpine terrain, many debris piles had no obvious crowns above them. The majority of the slides that were observable appeared to have failed at the new-old interface (we are calling this 11/27). Activity was most pronounced on the northern portion of the compass, though a number of slides were visible on E-SE facing slopes. To generalize, these appeared to have failed later in the storm than slides on northerly aspects, but there were plenty of exceptions to this rule.
A more thorough accounting of these slides will follow, as time allows.
Primary objective was to get up high for a good view of the surrounding mountains to look for recent avalanche activity and to see what the storm had done. We observed widespread wind-afftected snow, stretching down to the valley bottoms in some locations. Large drifts, dunes, and scalloped snow textures were observed. There was evidence of wind blowing from the SW-S-SE during the storm and from the NW after the cold front passed. In the alpine terrain we observed, many exposed ridgelines had been blown free of snow.
We dug in two locations along the ascent (E-NE) to look at how the new snow was bonding internally and to the the older snow underneath. In both locations we found a mid-storm interface down 30cm that produced propagating fractures in ECTs with easy to moderate force. This layer also appeared to partially collapse on isolation several times. This subtle density change was also observed the previous evening. I'd expect this to be short-lived and trending towards healing. In both pits there was also a thin (3-6cm) wind skin built on top of the snow that was poorly bonded.
The 11/27 interface was buried down 50-60cm where we dug. To my surprise, this old snow looked better than what I've observed elsewhere—smaller grains, less advanced faceting, and a bit harder. My hunch is that winds had been "cleaning" this surface as it formed in this location, removing the worst of the facets. We were still able to get propagating results with ECTs, but the layer also produced several ECTNs. The widespread avalanche activity that occurred during the storm is the best evidence of the nature of this layer. I'm thinking of these pits as more of an outlier than a trend until I see significant evidence otherwise.
A radiation recrystallization crust formed at the surface here today, and had already refrozen by mid-afternoon. This layer consisted of 1cm of cold, faceting snow on top of a 1cm crust. This has the potential to be a touchy weak layer on roughly SE-S-SW once loaded.
Problem | Location | Distribution | Sensitivity | Size | Comments |
---|---|---|---|---|---|
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Weak Layer(s):
Nov 27, 2022 (FC)
Comments: Rose shaded based on where problem is expected to exist in our location. S-SW-W -facing slopes at lower elevations were largely free of snow prior to this storm. |
We did not even entertain the idea of entering avalanche terrain where 11/27 existed as a well-connected layer of snow.