Northwest Avalanche Center

Observation: Public

All Observations

Observation Details

Name:
LL, ALL, NH-S
Observation Date:
February 2, 2022
Submitted:
February 2, 2022
Zone or Region:
Stevens Pass
Activity:
Skiing/Snowboarding
Location:
Nason Creek to 5000'

Observed Avalanches

Did you observe any avalanches? 
Yes
Avalanche Type:
Dry Loose (Sluff)
Size:
Size 2: Could bury, injure, or kill a person
Elevation:
4500'
Aspect:
S
Comments:
Large gullies ran mid-storm 1/31 or early 2/1 on the southern flank of Lichtenberg.

Signs of Unstable Snow

Did you see shooting cracks? 
No
Did you experience collapsing or whumpfing? 
Yes, Isolated

Observations

Calm day giving way to breezy conditions and light to moderate snow. We had a dig at 5000' on a southwest slope where there was evidence of some wind loading. PST50 end on facets over the 1/30 crust and high single digit CTs on the density change. CTs in mid teens on preserved stellars. ECTN16 on stellars.

Most obvious red flags were around 3300-3500' in flat valley bottoms that had stayed cold during the inversion, where we had a dozen small to medium collapses. We saw much old wet loose debris on steep features 4000-5000' on Lichtenberg mountain, but didn't notice any crowns from recent slab avalanches.

We stayed below ridgeline all day and avoided northerly aspects given that prior travel showed more weak snow on polar aspects. It will be interesting to see if the incoming wind/precip and subtle warm-up activate the interface we tested on other aspects and ATL.

Media

PST50 end over crust at 50cm down.
Sleeted over stellars.
Density change in storm snow (above) and over preserved stellars (below)
Dry loose debris in the SW shot of Lichtenberg
Facets over crust were more active than anticipated in propagation saw test. Test column retained slab properties.

Advanced Observations

Observed Avalanche Problem #1: 
Persistent Slab
Comments: 
A variety of weak grains underlay the most recent storm: facets, surface hoar, freezing rain, wet grains. The facets and surface hoar were wet in several hand pits to 5k' as the weather warmed before the storm.
Observed Avalanche Problem #2: 
Storm Slab
Comments: 
Within the recent storm (HST to 50cm), there are several interfaces, including preserved, iced stellars 25-30cm down and a density change mid-storm interface 15cm down.
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