Observation: NWAC Forecaster

All Observations

Basic Information

Observation Details

Observation Date:
December 13, 2021
Submitted:
December 13, 2021
Observer:
NWAC Forecaster - Matt Primomo
Zone or Region:
Stevens Pass
Location:
Rock Mountain (SE-SW 2800-6,200. NE at 6,200.)

Signs of Unstable Snow

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

Media/Attachments

Profile on an E aspect at 5,300ft with arrow to the layer of concern, just above the crust.
Drifts covering the skin track a few hours later are a sign that wind is drifting snow.

Advanced Information

Weather Summary

Cloud Cover:
Overcast
Wind:
Moderate , E
New/Recent Snowfall:
5-8cm during the day

Overcast skies led to obscured as we ascended and a wave of moderate snowfall came in that lasted through the afternoon. E winds transported snow in moderate amounts in exposed areas.

Avalanche Observations

 #  Date Location Size Type Bed Sfc Depth Trigger Photos Details
3 Dec 11, 2021
() 		Rock Mountain lower gully
SE 4000ft 		D2 SS-Soft Slab N-Natural
Looking down the gully, debris has some fresh snow over it.
Report
Rock Mountain lower gully

A number of the steep SE facing gullies ran naturally as D2 soft slabs, estimated on morning of Saturday 12/11. See associated avalanche occurrence.

Snowpack Observations

HS was measured at a few different elevations/locations:
3,800ft: 90cm
4,900ft: 120cm
5,300ft: 160cm
6,200ft: 200cm

The hardness profile is generally favorable with F snow on the surface in most areas outside of recent wind effect down to 1F+ or so above the crust from December 8. This crust presents as a translucent freezing rain crust and is consistently 3-5mm thick, and down 90cm-120cm from the surface. We found small grained (0.5-1mm) rounded facets above and sometimes below it. We targeted this layer for some tests at 5,300ft on E, 6,200ft on SE, and 6,200ft on NE.
We got consistent Sudden Planer results with Compression Tests (CTH) on 1mm rounded facets above the crust at the 5,300ft site.
The other sites revealed no results on this layer, but did receive Resistent Planer failures (CTM) 50cm down on a density change on the SE aspect at 6,200ft.

Avalanche Problems

Problem Location Distribution Sensitivity Size Comments
Wind Slab
Isolated
Specific
Widespread
Unreactive
Stubborn
Reactive
Touchy
D1
D1.5
D2
D2.5
D3
D3.5
D4
D4.5
D5
 Comments: Small, shallow wind slabs forming on exposed slopes due to E winds.
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