Turnagain Pass Avalanche Forecast

With the active weather pattern continuing and the possibility of natural avalanches, today is a day to stick to low angle terrain and avoid avalanche runout areas. Yesterday morning brought a pulse of  3-6″ of light fluffy snow that was followed by rising temperatures, heavier snow and rain overnight (with rain/snowline around 1500′).

24 hr storm totals:

• Turnagain Pass at 1,880′:  0.7″ of water equivalent, roughly 8-12″ of snow above treeline.
• Girdwood Valley at 1,700′:  1.31″ of water equivalent, roughly 1-2′ above treeline.
• Portage Valley at sea level:  1.23″ of water equivalent, roughly 1-2′ of snow above treeline.
• Summit Lake at 1,400′: 0.3″  of water equivalent, roughly 5-8″ of snow above treeline.

With heavier snow falling on lighter snow and the old surface snow being weak, expect storm slabs to be sensitive today. In addition, below 2500′ this will all be resting on top of the rain crust. This could easily act as a bed surface with the weak snow sandwiched between it and the storm snow. Observers yesterday noted snow not bonding well to the crust. Steady ridgetop winds will have transported snow to leeward terrain and created touchy wind slabs. Cornices will also be larger and more sensitive to triggering today. Look for roller balls and loose snow avalanches at low elevations as rain falls onto dry snow. With all these storm related avalanche issues today use good travel protocol, avoid small terrain trap features and look for signs of instability.

Red flags to watch for:
–  Recent avalanches, from yesterday or today?
–  Whumpfing (collapsing) of the snowpack.
–  Shooting cracks, likely to be seen near ridgelines where the wind has formed wind slabs.

Corniced ridgeline on Notch Mountain, 12.6.20. Expect cornices to be sensitive today.

Sparkling surface hoar and small near-surface facets are now buried at the new snow/old snow interface and could be quite reactive today. Photo: Manitoba. 12.5.20

The stout rain crust to around 2500′ has the potential to act as bed surface. Crust @ 2400′, Notch Mountain. 12.6.20

Another reason to keep it mellow today is that once you travel into terrain where the stout rain crust ends (around 2500′), we cannot rule out the potential for large avalanches failing at the ground. Weak, faceted snow still exists at the bottom of the snowpack. Saturday’s snowboarder-triggered avalanche on Silvertip is reminder of this lingering deep slab avalanche problem. Snowfall and wind-loading will add stress to the snowpack and an avalanche failing in the in the upper snowpack or a cornice fall could make these more sensitive today.

Cornice triggered deep slab in upper Bertha Creek (Gold Pan). Photo from 12.4.20 by Alan Abel. Cornice falls today could trigger deep slab avalanches.