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Observation: Turnagain

Location: Sunburst

Date:
Observer:
Route & General Observations

Sunburst normal up track to 2200′. Above 1800′ widespread collapsing. Could make out a large slide path of an avalanche on SW face of SB that was remotely triggered on Monday, Dec. 4 mid storm.

Investigated a skier triggered avalanche that also occurred on Dec. 4 by the same party at 1900′ on SW aspect. We could just barely make out the crown, debris and an old track. The steepest slope angle was 32 degrees and averaged 27 degrees. Not very steep. Old crown looked to be about 60′ wide. May have only been storm snow. We dug a pit and found a 2′ slab on a layer of basal facets sitting on a thin melt/freeze crust on ground. Facets were cupped and 3-5mm in size. See photo below. Tests: CT23, ECTX, PST30/100 Arrest on facets/crust bed surface, CT11 failed 25cm below surface on density change.

Above this elevation the snow became more wind affected and denser, but still felt upside down near ground. Dug a second pit at 2200′ after experiencing several big ‘whumphs.’ The height of snow ranged from 30cm to 120cm and collapsing was more common in places where the slab was thinner. Test were more reactive than in the first pit with propagation on 2 of 4 Extended Column tests. Facets/crust combo was anywhere from 55cm to 90cm in this pit location. Slab was 1 Finger hard.

Red Flags
Red flags are simple visual clues that are a sign of potential avalanche danger. Please record any sign of red flags below.
Obvious signs of instability
Recent Avalanches?Yes
Collapsing (Whumphing)?Yes
Cracking (Shooting cracks)?Yes
Observer Comments

Remotely triggered avalanche on Tincan today at 2:15. See Road obs/Tincan avalanche posting.
Widespread collapsing above 1800'

Weather & Snow Characteristics
Please provide details to help us determine the weather and snowpack during the time this observation took place.
Weather

Clear
Temps cooled from 30F in morning to 19F at 3pm along road
Light E. wind decreasing to calm
No precip

Snow surface

4" low density snow from yesterday morning with a thin layer of graupel on top

Snowpack

900'-1500' - Top 5" breakable crust. This crust had a variety of layers as you ascended above 1000' including a thin drizzle crust with dry snow above and below it.
At 1900' a 1cm wafer like crust was still present 40cm below surface

Pit at 2200', WSW aspect, 29* slope, HS=65cm-95cm across pit wall. Tests: CT8, ECTP11x2, ECTX, ECTN12, PST45/100 End. All failed on facet/crust combo near ground.

Photos & Video
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