Observation: NWAC Forecaster

All Observations

Basic Information

Observation Details

Observation Date:
December 28, 2022
Submitted:
December 28, 2022
Observer:
NWAC Forecaster - Dallas Glass
Zone or Region:
West South
Location:
Crystal backcountry: East Peak, Cement Basin, Lake Basin (All aspects near and below treeline. (4300-6700ft) )

Signs of Unstable Snow

Recent Avalanches? 
Yes
Cracking? 
Isolated
Collapsing? 
None Experienced

Media/Attachments

Snow blown out of the tops of trees clued us into the potential wind loading even though we were still below treeline.
Wind textrured snow near ridge crest.
This small wind loaded pocket easily failed on a very small test slope.
Cornices along ridges were not huge, but they failed very easily and much further back than we expected.
1/2in of ice was plastered on the south side of tree trunks and branches.
Ice encrusted branches were see throughout the near treeline band.
Creeks that had once filled in, were again open and flowing high after all the rain.
https://www.youtube.com/shorts/XqMPq7sBmjg

Advanced Information

Weather Summary

Cloud Cover:
Mostly Cloudy
Temperature:
20°F
Wind:
Moderate , W
New/Recent Snowfall:
Below Treeline: 6 in (15cm), Near Treeline 8-9 in (20-23cm)

Cold and blustery. Winds were moderate, but with stronger gusts. Only a few very light snow showers during the day with no accumulation.

Avalanche Observations

 #  Date Location Size Type Bed Sfc Depth Trigger Photos Details
1 Dec 24, 2022
() 		Lake Basin, Crystal backcountry
NW 6500ft 		D2.5
R2 		WS-Wet Slab O-Old Snow N-Natural
An older very large avalanceh that appeared to have failed during the rain over Christmas weekend. NW, 6500ft, WS-N-D2.5-R2-O
An older very large avalanceh that appeared to have failed during the rain over Christmas weekend. NW, 6500ft, WS-N-D2.5-R2-O
The debris from an older wet slabs that likely occurred over the Christmas weekend.
Report
1 Dec 28, 2022
() 		Norse Peak
E 6600ft 		D2
R1 		HS-Hard Slab NC-Cornice Fall
A natural cornice fall triggered a large wind slab avalanche in Lake Basin, Crytal backcountry. This slide looked less than 24hrs old. E, 6600ft, HS-NC-D2-R1-U
Report
Lake Basin, Crystal backcountry
Norse Peak

We also observed 1 older natural cornice fall off of East Peak (E, 6600ft) and what appeared to be buried debris from a wet slide in the same area (East Peak, NNE, 6600ft).

Snowpack Observations

Wind Slabs:
There were plenty of signs of newly forming wind slabs in the terrain: variable new snow depths, scoured slopes, firm hollow drifts, textured surfaces, snow blown out of trees, blowing snow, sharp drifts, and small fresh cornices. Drifts were 4-20 in (10-50cm) deep. These clues indicated direct loading at ridgelines and cross-loading on mid-slope subtle features. Small wind slabs cracked and failed on numerous test slopes. The thinner slabs seemed to be much easier to trigger.

Many of these wind slabs were hard slabs, with skis sometimes barely penetrating the surface.

Cornices: Many typical cornice lines were eroded back from the recent rain and have yet to rebuild. However, where cornices had formed they triggered easily and failed further back than expected.

Wet Snow:
Below the fresh snow, a newly forming crust was found. This layer was much firmer and more supportive where the wind had scoured the slopes and exposed the older rained-on surface. In these places, it was often 3-4in (~8-10cm) thick and very hard, but still not boot-supportable. Where more snow insulated the crust, it was thicker (8-12in, 20-30cm) but weaker. Below these crusts, wet grains were found for 3-5ft (100-150cm). When our boots punched through the crust, we often plunged to near waist deep.

Ice had formed on most tree trunks and branches during the Christmas weekend rain/freezing rain event.

Other obs:
You could hear creeks running in every valley. Many gullies that were once full of snow, were now open, and water was running fast and high.

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

I still wouldn't rule out a wet slab or glide avalanche, but we did not make any significant observations or current wet issues.

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