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Missoula Avalanche

Professional Observation

Basic Information

Observation Details

Observation Date:
December 29, 2021
Submitted:
December 30, 2021
Observer:
WCMAC - George D'Angelo
Zone or Region:
Southern Bitterroots
Location:
Lost Trail Backcountry

Signs of Unstable Snow

Recent Avalanches? 
None Observed
Cracking? 
Isolated
Collapsing? 
None Experienced
Small unstable cornices and reactive wind slabs at ridgelines at and above treeline.

Snow Stability

Stability Rating: 
Good
Confidence in Rating: 
High
Stability Trend: 
Steady

Bottom Line

The lingering deep slab instability and small wind slabs are what you should be focused on today in the Southern Bitterroots. The persistent weak layer (PWL) shows signs of propagation down almost 4ft. Be wary of shallow, NW-E aspects at mid and upper elevations. Wind slabs will continue to grow if winds materialize as forecast. These will most likely be isolated to ridgelines at treeline and above. South facing mid-elevation slopes have a melt-freeze crust down about a foot worth observing. These southerly slopes do not appear to have a uniform persistent weak layer (PWL), but it's worth checking to see if it exists, especially at upper elevations. PWLs on southerly or wind-scoured slopes will likely be easier to trigger than their shaded, wind-protected counterparts.

Media

Advanced Information

Weather Summary

Cloud Cover:
Mostly Cloudy
Temperature:
-14*C
Wind:
Light , W

Light snow accumulations and moderate winds should keep snow available for wind slab/cornice formation at ridgelines.

Terrain Use

We skied a 30* soft, south facing, mid elevation slope and found some early season hazards still exist. We avoided the deep slab problem on the northern slopes

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