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Observation: Turnagain

Location: Tincan

Date:
Observer:
Route & General Observations

Ascended to 2660′ veering slightly South off the standard uptrack and descended the trees. The most significant wind affect I have seen all year in Turnagain.

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)?No
Cracking (Shooting cracks)?Yes
Observer Comments

Shooting cracks and a small shallow wind slab was triggered off a Northerly aspect near treeline. Photo below. This hard wind slab failed on decomposing/broken stellar dendrites over a melt freeze crust and occurred in an area where the snow was pretty thin as this area has been getting scoured most of the year.

Northerly winds transporting snow off Tincan Common and Hippy bowls, loading the Southerly aspects observed around 10:30 am. For a brief period in the afternoon, Southerly winds were transporting snow off Sunburst at ridgetops, loading the Northerly aspects.

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

Upper 30s F at valley bottoms decreasing to 20s at ridgetops. It was the first day out touring this year where I wished I had worn a T shirt! Light winds the whole tour along our mid-elevation route. Clear skies. No precipitation.

Snow surface

Roughly 7" of settled snow from Feb 12th. Below treeline there were many signs of wind effect on South and West aspects, but the snow surface was still soft with only some areas having 2" wind crust. Little wind effect noted on East and North below treeline. Above treeline, the snow was heavily wind affected with wind crust, wind slab, sastrugi and anti-tracks, which also made for challenging ski conditions.

Given all the signs of wind texturing, we were surprised to find wind slabs were more isolated and surface clues didn't always point to where they were, instead we often found light wind effect and settled powder.

Wind effect in Turnagain Pass in general was most noticeable on the non-motorized side of the road, with wind affect visible on nearly every peak.

Snowpack

A few hand pits failed easily (5-7" down) in the trees on either the Feb. 5 BSH or new/old interface in areas where there was more of a wind slab. Above treeline hand pits failed on isolation, easy, and under moderate force on the new/old interface (down 5-9"). Sometimes these failures were clean and planar, and other times they were rough breaks.

We dug a pit at 2660'. See pit profile below. We found the Jan. 21 BSH 65 cm down, as well as what we originally thought was the Feb. 5 BSH (see the thin gray line in the photo below) but turned out to be a thin 1cm layer of very low density, intact stellar dendrites sandwiched between a 4F wind slab and thin, dense 1F layer of snow.

Photos & Video
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