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Professional Observation

Basic Information

Observation Details

Observation Date:
January 6, 2020
Submitted:
January 6, 2020
Observer:
SAC - VandenBos
Zone or Region:
Sawtooth and Western Smoky Mtns
Location:
Imogene

Signs of Unstable Snow

Recent Avalanches? 
None Observed
Cracking? 
Isolated
Collapsing? 
None Experienced
Cracking in specific areas, those where fresh wind drifts were resting on still, wind polished surface underneath.

Snow Stability

Stability Rating: 
Fair
Confidence in Rating: 
Moderate
Stability Trend: 
Steady

Bottom Line

Ongoing snowfall and wind loading is keeping the snowpack on its toes, particularly in the alpine. In sheltered terrain, the interface that we buried on 12/31 looks like it may produce continued instability, at least in the short term.

Advanced Information

Weather Summary

Cloud Cover:
Overcast
Wind:
Moderate , SW

In and out of the clouds this afternoon. Periods of S-1 snowfall, southerly winds continuing to drift snow, loading northerly slopes. Lots of snow available for transport at middles, less up high.

Avalanche Observations

 #  Date Location Size Type Bed Sfc Depth Trigger Comments Photo
1 Within the past week NE Imogene
NE 10,000 		O-Old Snow 2-3' N-Natural Deep crown in NE chute off Imogene. Tough to estimate size without seeing debris, which was obscured by blowing snow and low clouds.
This crown from a large natural avalanche was observed on 1/5/2020, but the avalanche likely failed during the storm around new years. It released on a NE aspect at 10,000' on Imogene Peak in the southern Sawtooths. Based on crown depth, it appears to have failed on a layer of weak snow buried deep in the snowpack.

Not entirely sure if this is an outlier or a sign of whats to come. Very little activity reported from this area from New Year's storm.

Snowpack Observations

Was curious about how middle elevation solars were looking in our normally wetter terrain, particularly 12/7 and 12/31 interfaces. No intact SH found at 12/7 where I dug, on a sheltered, open, SE-facing slope at 8,250' where HS=75-80cm. 12/31 presented as subtle MFcr with near-surface facets above. This interface generated very unstable snowpack test scores (ECTP 1 and 2). Quite touchy, given that there is just a F to F- slab on top. Will be something to watch with additional loading.

Avalanche Problems

Problem Location Distribution Sensitivity Size Comments
Persistent Slab
Isolated
Specific
Widespread
Unreactive
Stubborn
Reactive
Touchy
D1
D1.5
D2
D2.5
D3
D3.5
D4
D4.5
D5
 Layer Depth/Date: 12/31 down 30cm
Not sure how reactive this is without the crust - shaded location rose based on thought that crust is probably an important component.
Persistent Slab
Isolated
Specific
Widespread
Unreactive
Stubborn
Reactive
Touchy
D1
D1.5
D2
D2.5
D3
D3.5
D4
D4.5
D5
 Layer Depth/Date: 11/26
MFcr/DHxr with 2-3mm FC above
Wind Slab
Fresh slabs were confined to upper elevations, but older slabs were present well down into middle - product of the end of the year wind event.
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