Observation: NWAC Forecaster

All Observations

Basic Information

Observation Details

Observation Date:
January 1, 2022
Submitted:
January 1, 2022
Observer:
NWAC Forecaster - Irene Henninger
Zone or Region:
West North
Location:
Shuksan Arm (N, W 4000-5500ft)

Signs of Unstable Snow

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

Media/Attachments

A crown profile displaying the surface hoar line which is what the avalanche failed on. In this location, the surface hoar was 70cm below the surface. Past our location it deepened to a max depth of about 150cm.
Large blocks which didn't travel very far on the lower angle sections at the top of the avalanche on the Shuksan Arm.
Surface hoar found at the crown profile, the layer the avalanche failed on.
Cracking in a stiff wind feature was seen on the bootpack along the arm. Probably occurred yesterday as someone walked by.
https://www.instagram.com/p/CYNhQOboStv/

Advanced Information

Weather Summary

Cloud Cover:
Overcast
Temperature:
18°F
Wind:
Light , SE

The cloud ceiling was at about 8000ft. Cold! Occasional moderate wind gusts were still transporting small amounts of snow, but the major event was yesterday and textured, firm snow surfaces were aplenty.

Snowpack Observations

A crown profile was conducted on the very large avalanche that occurred yesterday on the Shuksan Arm:

The snow depth where we dug was 370cm, and the thin (Solstice) surface hoar layer which the avalanche failed on was 70cm below the surface. From the surface, the top 10cm were 1Finger hard (wind-affected), and the 10cm below that were Fist hard, and there were barely discernable .5mm faceting (weak) forms in that layer. Beneath that was decomposing forms and rounds slowly increasing in hardness from 1 finger to pencil hard all the way to above the surface hoar layer.

3mm surface hoar crystals (persistent weak layer which the avalanche failed on) were still well developed and easily identifiable, both in the pit wall and on a crystal card. Other areas along the crown wall had crown heights up to about 150cm. Avalanche width was around 500ft, and we estimate it ran 800-1000ft, but were unable to see the final debris pile as it was hidden behind a roll.

On the return trip, we found wind-affected snow until about 4500 feet: Some areas were very slabby and made for challenging skiing, while a shift over a subtle feature would then deliver us onto low-density powder.

Avalanche Problems

Problem Location Distribution Sensitivity Size Comments
Deep Persistent Slab
Unknown
Unreactive
Stubborn
Reactive
Touchy
D1
D1.5
D2
D2.5
D3
D3.5
D4
D4.5
D5
 Layer Depth/Date: 70
Comments: SH/weak layer starts at about 4800ft in elevation and up, and unclear as to its' distribution- many areas were destroyed before they were buried 12/21 (Solstice)
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