Turnagain Pass

Another round of easterly ridgetop winds hit the region last night as a small weather system is moving through currently. Overnight, between 1-3″ of new snow has fallen and another 1-2″ is expected for today; this is above 400′ as below, light rain is expected. The ridgetop east winds were blowing 20-30mph from 8pm last night till around 2am this morning before quieting down to 10-20mph, where they should remain for the day. This said, we can expect some fresh wind slabs out there in exposed areas in addition to lingering wind slabs from earlier in the week.

Most of these fresh slabs are likely to be in the higher elevations, around a foot thick, and possible to trigger. With today’s poor light, travel into the Alpine may be somewhat thwarted, but finding these in the mid-elevations is also possible. While most older wind slabs seem to be fairly stuck into place, there is still a chance a few lurking stubborn slabs could pose a threat on just the right steep wind loaded slope. Keeping a close eye out for the classic wind slab tell-tale signs will be key.

Classic wind slab signs:

• Rounded and pillow-like surfaces (wind deposited snow)
• Hollow feeling or drum-like feeling on the snow due to stiff snow over softer snow
• Cracks in the snow that shoot out from your machine, skis or board
• Any collapsing in the snow or ‘whumpfing’
• The skiff of new snow from today may be obscuring some wind slabs

A couple ‘Normal Caution’ avalanche issues: On steep slopes out of the winds where loose surface snow is found, keep an eye on your sluff. And, as always, give cornices a wide berth and limit time under them.

Impressive wind effect along Seattle Ridge around 2,500′. 12.29.20. Photo: Beau Gehler

On mid-elevation slopes (1,300′ – 2,500′) we have been tracking a crust that formed on 12/1. This crust is degrading, developing a thin layer of facets, and beginning to show signs of forming a reactive weak layer in some areas, but not all. The crust sits 3-5′ below the surface and has been responsible for large avalanches trigged with explosives and a large collapse at Pete’s North. Triggering an avalanche on this layer is unlikely but could have bad consequences. Signs of instability will not likely be present and stability tests could give unreliable data. Steep unsupported slopes in the 1300′-2500′ elevation range should be considered suspect and there may be multiple tracks on the slope before it fails.

The Summit Lake region to the south of our forecast area has a thinner snowpack with faceted snow at the ground that is a concern above 2500′.  This area also has the December 1st crust/facet combo below 2500′. Both these weak layers are worth keeping in mind before trying to push into bigger terrain in the Summit Lake area.

Snow pit at 2,300′ on Seattle Ridge. This is representative of the Repeat Offender slide path. No instability was found. The crust here, despite degrading and faceting, was not reacting in the pit the way some pits have been on the non-motorized side of the Pass.