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Professional Observation

       

Basic Information

Observation Details

Observation Date:
December 4, 2022
Submitted:
December 4, 2022
Observer:
Everett Phillips | ESAC Forecaster
Zone or Region:
Mammoth Lakes
Location:
Lakes Basin - Persistent Slab Avalanche Below Treeline

Signs of Unstable Snow

Recent Avalanches? 
Yes
Cracking? 
None Experienced
Collapsing? 
None Experienced

Key Points

The goal of this afternoon’s tour was to find a safe vantage point to take photos of a large natural avalanche that was reported in Redcone Bowl. Unfortunately, visibility did not cooperate and I ended up focusing on evidence of persistent slab activity Below Treeline.

  • As of this afternoon the new snow from last night and this morning is both wind affected and settled enough that it supports the weight of a skier. Ski testing and skintrack assement can only really provide feedback on the uppermost storm layers.
  • The recent avalanche I observed was large enough to bury a rider even on the very short slope it released on. It was a good reminder of how important it is to be diligent about staying out from under all slopes steep enough to slide during High danger.
  • The avalanche failed on the same layer as the one observed along Minaret Vista road on 20221202. It may have been initially triggered by a failure within recent wind deposited storm snow.

 

Media

Profile of a large persistent slab avalanche Below Treeline in the Mammoth Lakes Basin
Crown of a large persistent slab avalanche Below Treeline in the Mammoth Lakes Basin
Close up of a section of the crown of a large persistent slab avalanche Below Treeline in the Mammoth Lakes Basin.
Deep avalanche debris from a D2 avalanche on a relatively small slope Below Treeline in the Mammoth Lakes Basin

Advanced Information

Weather Summary

Cloud Cover:
Obscured
Temperature:
25F
Wind:
Light , W

Clearing skies in the over Mammoth Lakes Basin.

Light to Moderate W winds at 9500′ in the forest.

Temp. 25 F at 9500′ and falling fast.

Sky obscured by lingering storm clouds and blowing snow on the crest.

Very light snowfall decreasing from afternoon into the evening.

Avalanche Observations

 #  Date Location Size Type Bed Sfc Depth Trigger Comments Photo
1 Past 24 hours Knoll North of McCloud Lake
NE 9400' 		D2 SS O-Old Snow 100 cm N-Natural Crown ranges from 50-100cm, is approx. 35m wide and connects around terrain features in steep rocky open forest. The avalanche ran approx. 30m downhill into low angle forest. There are two distinct failure planes. The first is a storm interface down 35cm. The lower failure plane is down 100cm at the top of the faceted snow buried on 20221201. None

None

Snowpack Observations

BTL Mammoth Lakes Basin:

HS: 165cm

HST ~ 50 cm

1m of snow from this week’s storms sits on old faceted snow from late November’s dry spell.

Storm snow is still fist hard, but is moderately supportable (ski pen – 10- 20cm).

Surface form is wind broken precipitation particles.

 

 

 

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