Turnagain Pass Avalanche Forecast

Yesterday was a classic sunny Saturday after a storm cycle and many folks were out enjoying Winter Part III. Along with this were reports of a handful of large human triggered avalanches. Luckily, no one was reported caught as they were 3-5’+ deep, large and dangerous. Details are limited, but here is what we know:

–  Widow Maker Face (West facing, 2,500′ – Seattle Creek drainage). This avalanche was 5-6′ deep and likely remotely triggered from the ridgetop by a group of riders. More details HERE.

–  Four deep pockets in Tincan’s Hippy Bowl (Southwest facing, 3,500/3,000). These slides are suspected to have been remotely triggered from an adjacent sub-ridge. More details HERE.

–  Palmer Creek (South of Hope). At least one large snowmachine triggered avalanche was reported in this drainage – very little information at this time.

Photo below: Widow Maker avalanche – photo was taken by a person looking North on Seattle Ridge.

The avalanche activity noted above is suspected to be failing at the old snow/new snow interface. The new snow consists of the combined 3/10-3/14 storm snow that has settled into a very strong slab around 30″ to 4′ thick (thicker in wind loaded areas). The weak layer is suspected to be a thin 1-2cm layer of old weak snow and buried surface hoar sitting above the late February crust.

Lowering likelihood – high consequences:
The slab is thick enough that triggering the weak layer is difficult and the weak layer is showing signs of adjusting to the new load. However, this set up deserves our respect regardless. The sole reason is the sheer size and destructive power of a potential slide. If you haven’t noticed from the reports of yesterday’s activity, these are deep and dangerous avalanches – the kind that if you are caught up in, are likely not getting out of. Conservative terrain management is key once again for a safe day in the backcountry.

Ridgetop winds are forecast to pick up to ~20mph from the East by noon today and continue to increase into the 40-50mph range by tonight. Although only around an inch of new snow is expected this afternoon, there is upwards of 4-10″ of loose snow already on the surface available for the wind to transport. With these factors in mind, watch for winds to form slabs near ridgelines, on rollovers or by cross-loading in gullies. These slabs will likely be in the foot deep category and sensitive to human triggers.

Additionally, any wind loading and/or wind slabs triggered could stress buried weak layers and aid in triggering a deep slab.