Observation: NWAC Forecaster

All Observations

Basic Information

Observation Date:

December 30, 2021

Submitted:

December 30, 2021

Observer:

NWAC Forecaster - Irene Henninger

Zone or Region:

West North

Location:

Hwy 20 - WN (S-W, 1200-4500ft)

Recent Avalanches?

Yes

Cracking?

None Experienced

Collapsing?

None Experienced

The first of many very small storm slab avalanches we encountered during the day, all having partially filled in since they slid.

Half of this snow-covered rock had a mini avalanche, and the adjacent slope cracked and slid a few inches, only on the subtle rollover that was 1 or 2 degrees steeper than the surrounding terrain.

Cracking was visible in several spots on this large slope from instabilities peaking during the storm overnight.

This compression test easily identified where storm slab failures occurred during the storm overnight.

Advanced Information

Cloud Cover:

Clear

Temperature:

24°F

Wind:

Calm

New/Recent Snowfall:

22cm overnight

Heavy snowfall (S4) died down at 0830hrs. Skies cleared fully by 1100hrs but 2 hours later skies became obscured for a couple hours, before partly clearing again. Mixed bag! Slight signs of snow transport from early this am were present above 4000ft, but all snow remained very low density. Around a foot more snow at the surface is easily available for transport.

Avalanche Observation Comments:

Several small and very small storm slab avalanches running during last night's storm were visible today. Even signs of weakness in areas not steep enough to slide. (Cracking was seen on moderate angle slopes). There were about 3 inches of fresh snow coating the slides. They ran on the new snow/old snow interface.

8 inches to a foot of last night's storm snow was overlying the Dec 26-27 snow. The new snow was reactive during the storm and was not reactive where we traveled during the day with either natural or human-triggered avalanches. The Solstice Crust was buried about 3 feet down, and we did not get any test results on that layer.

Problem	Location	Distribution	Sensitivity	Size	Comments
Storm Slab	N E S W	Isolated Specific Widespread	Unreactive Stubborn Reactive Touchy	D1 D1.5 D2 D2.5 D3 D3.5 D4 D4.5 D5	Layer Depth/Date: 22cm/Dec-30 Comments: Mainly very small avalanches on nearly all steep slopes were seen, but only during the storm. Sensitivity decreased greatly since.

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