Observation: NWAC Forecaster

All Observations

Basic Information

Observation Details

Observation Date:
February 1, 2022
Submitted:
February 1, 2022
Observer:
NWAC Forecaster - Matt Primomo
Zone or Region:
Stevens Pass
Location:
Henry Creek (NW-NE to 4,300ft)

Signs of Unstable Snow

Recent Avalanches? 
None Observed
Cracking? 
Isolated
Collapsing? 
Isolated

Media/Attachments

View across the highway to the south side of Rock Mountain.
Faceted grains within a crust from a north aspect at 4,000ft where we had a large whumph.
~50cm over facet/crust layer in area where it collapsed.
Rough outline of a collapsed slope which produced a very large whumph.
100ft long shooting crack on crust/facet layer.
Great skiing in lower angled terrain below 4,000ft.
N at 4,000ft Henry Creek. CT 11 SC down 50cm beneath 1/30 (1cm IFcr on 1mm FC and some larger SH) over stout MFcr from 1/20. This was in slope that had already collapsed- A large whumph, maybe 20m around. Bryce Hill photo.

Advanced Information

Weather Summary

Cloud Cover:
Obscured
Wind:
Light , W
New/Recent Snowfall:
14-18"

Scattered snow showers, light to moderate at times. Light blowing snow observed.

Snowpack Observations

We ascended the road up to around 4,300ft. As we gained elevation we found more and more wind thickened snow. At around 4,000ft while breaking trail in a deeper drift, we had a loud sudden whumph! and a slope about 60ft around us collapsed. It was starting and quite large.
Digging down, we found about 20" of drifted snow over a mix of facets and melt forms buried on January 30th, resting over the stout crust from the 20th. This layer produced results with compression tests as well, even though the slope had already collapsed (CT11 SC).
A little higher and further away we found a very thin rain freezing rain crust overlying very weak facets over the stout crust. Here we were able to get very long shooting cracks in wind drifted road cuts (up to 100ft long or so). This facet/crust sandwich was quite prevalent as we traversed the road near the top of the clearcuts. We ran into some other folks who had skinned directly up the slopes to the upper road we were on. They experienced some 'tree shaking' whumphs on their way up once gaining the ~4,000ft elevation.

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