Avalanche: Turnagain

Location: Sunny Side

Route & General Observations

Skied the southern end of Seattle Ridge. The snow was inconsistent, but generally fun turns.
We had a large (20-30yd diameter?) whump at 1,200ft. We had another bigger whump (60yd diameter?) that was strong enough to knock berries off of bushes 20yds away. We stopped to dig near that the second whumph. Our pit results confirmed what the forecast has been saying for several days. There are slabs in the snowpack with 2 significant weak layers that can propagate. We already had planned a mellow tour, we stepped it back a few notches more after the whumphs by ripping skins earlier in our laps to reduce exposure to steeper slopes above.

We skied a few laps in calm winds, but at about 2pm downslope winds picked up to 10mph+. Snow transport was incredible. Our skin track filled in in less than 30 minutes. In 1 hour our ski tracks were nearly erased (shin deep). We left.

Avalanche Details
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Trigger NaturalRemote Trigger Unknown
Avalanche Type UnknownAspect East Southeast
Elevation 2000ftSlope Angleunknown
Crown DepthunknownWidthunknown
Vertical Rununknown  
Avalanche Details

Two small (D1 R1) slab avalanches observed on the ESE face of Seattle Ridge. Photographs taken from the Sunburst parking lot.
These were of particular interest to us because we were planning to skin through similar terrain further south in the pass. Neither of the avalanches occurred in obvious (to me) spots for a natural trigger. Also, both are in terrain that is below 35deg slope according to my topo map.

Also, there is a large crown at the top of Cornbiscuit. It might be an old glide crack, but I think it is a more recent slab release. The edges aren't sharp anymore, but it is not as filled in as the other glide cracks near it.

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)?No
Weather & Snow Characteristics
Please provide details to help us determine the weather and snowpack during the time this observation took place.

Cold and Clear. Similar to last few weeks, the temperature drops quickly when descending south on the pass. 12F deg drop from Center Ridge lot to Bertha Creek.
Calm on the slopes we were skiing from 10am until 2pm, then 10mph downslope winds came on quickly.
Ridge top snow plumes seen most of the day on Pete's North and South, and on Fiddlehead (aka 4940).
No ridge top winds noticed at the northern end of Turnagain (Magnum through Eddy's)
Lot's of ridge top snow plumes seen on the morning and evening drives along Turnagain Arm -> Hope Point, Sunrise Peak, Alpenglow, Pyramid, etc

Snow surface

highly variable. Enough good skiing powder to be found in lanes, but also breakable wind board, hard wind slab, and zones with less than 10cm of snow over grass - all depending on topography exposed to previous days' cross slope winds from the North~ish.
Ski penetration while skinning was usually ~10cm.


Generally varied from 60cm to 100cm, but we measured everywhere from 6cm to 150cm in places along our skin track.
I tried jumping on and cutting a few rollovers and larger wind lip features along our skin track. I did not get anything to move.

We dug a pit at at 1650' elevation near a very big whumph.
East Aspect. Slope angle 32°. Height of snow in pit 85 to 110 cm

Stiffness profile:
95-80cm fist
80-70cm one finger
79-65cm four finger
65-40cm one finger
40-30cm four finger
28-15cm loose facets
15-0cm hard crust

CT 6 at 28cm,
ECTN 12 at 65cm, went about 1/3 across column
ECTP 22 at 65cm

Photos & Video
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