Observation: NWAC Forecaster

All Observations

Basic Information

Observation Date:

April 13, 2023

Submitted:

April 13, 2023

Observer:

NWAC Forecaster - Dallas Glass

Zone or Region:

West South

Location:

Crystal Backcountry: East Peak, Cement Basin, Lake Basin, Crow Basin, Norse Peak (All aspects near treeline)

Recent Avalanches?

Yes

Cracking?

Isolated

Collapsing?

None Experienced

An intentionally wind slab avalanche. SE, 6600ft, 8-10 inches deep, 30ft wide, failing on the 4/11 crust. HS-ACi-D1-R1-I

A long (12ft) shooting crack in a wind-loaded pocket.

This up-track test produced a long crack in a wind-loaded pocket.

These wind slab clues helped us determine the local wind patterns and potentially wind-loaded slopes.

Visual signs of the local wind direction.

Visual clues of potentially wind loaded slopes.

The new snow would occasionally fail right at the 4/11 crust interface.

This face produced a larger avalanche during the last major storm/rain event. NW, 6500ft

Old debris from the last major avalanche cycle litters the bottom of many slide paths.

Plenty of old debris around from the last major rain event.

Advanced Information

Cloud Cover:

Partly Cloudy

Wind:

Moderate , N

New/Recent Snowfall:

Recent Snow: ~6 inches (15cm)

Nice day! Overcast skies slowly broke and cleared. Periods of significant sunshine in the afternoon. Winds were a bit stronger than expected, but light to moderate out of the N with just a bit of blowing snow and drifting.

Avalanche Observation Comments:

New: We intentionally triggered one wind slab by kicking a very small cornice. The slab was about 30ft wide and ran to near the bottom of the feature.

Old: There are lots of piles of old avalanche debris from the last major cycle. The debris is covered by a few inches of snow and can be hard to see with out good light. While none of the slides we saw were huge, there appeared to be a descent D1.5-2 wet cycle during the atmospheric river event.

New Snow: The new snow was still very light dry and generally poorly bonded to the 4/11 crust. On steep sunny aspects, a very thin breakable surface crust formed on 4/12. Sunshine today, probably helped make that crust a bit thicker.

4/11 Crust: This layer is continuing to freeze and strengthen. It was boot supportable throughout our travels, but still not quite frozen solid. It's about a foot thick. As is freezes it should become quite stout! Below the 4/11 crust, the snowpack is still dry and layered. We could even find old storm interfaces.

Wind: The wind had redistributed the new snow near treeline. Scoured slopes, textured surfaces, small drifts, sharp cornices, and rime all spoke to the wind's effect. The predominate wind direction was from the North. This produces wind-loaded pockets and hard wind slabs in some unusual spots. While they weren't very widespread, when we did find wind-loaded features the typically cracked. We produced long cracks on small slopes and uptrack tests.

Sun: The sun did begin to soften the southerly slopes today, but we didn't encounter any unstable wet surface snow.

Problem	Location	Distribution	Sensitivity	Size	Comments
Wind 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

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