Turnagain Pass

It has been 5 days since the end of a 10-day storm cycle that brought 3-6′ of heavy dense snow and rain to the region. This snow fell on a widespread layer of buried surface hoar and unfortunately this layer continues to inhibit good bonding between the storm snow and the old March surface. As days pass, this layer of buried surface hoar is becoming more difficult to trigger. Furthermore, the fact that is sits over 3′ deep on many slopes also makes it more difficult to trigger. However, this should not lure us into thinking a slope is safe. Keep in mind thin spots in the slab, which is where an avalanche is most likely to be triggered, exist on all slopes and are tough to see and avoid – making this deep slab problem very tricky. Things to remember if heading out today:

1-  No signs of instability may exist before a large slab is triggered
2-  Slabs can be triggered remotely from below!
3-  Several tracks may be on a slope before someone finds the thin spot
4-  Daytime warming will increase chances for triggering a slab
5-  All aspects are suspect 
6-  These slabs are large and dangerous and nothing to mess with
7-  Low angle slopes continue to be your friend, with nothing steeper above you

*More details have come if from the several snowmachine triggered avalanches in the Seattle Creek drainage over the weekend. Please see the excellent write up and photos sent in to us from the close call where a snowmachiner was able to ride up and off a very large slab avalanche in Jr’s Bowl. 
 

Large snowmachinge triggered slab avalanche in Jr’s Bowl (2nd Bowl) on Saturday, April 8th. Photos, Cory Runa.

Crown was up to 10-12′ thick –  very large slab near the ridgeline where winds deposited snow during the 10-day storm cycle.

Large avalanche that was presumably triggered by a snowmachine on either April 7th or 8th on the NW aspect of Main Bowl (1st Bowl). Photo taken by Cory Runa on April 8th. Because of it’s safe and easy access, this is the avalanche that we closely investigated yesterday – flank profile and video below.

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Springtime is upon us and daytime warming below 2,000′ will again soften the surface crusts at the lower elevations and on Southerly upper elevations. While the upper elevation temperatures have remained relatively steady, in the mid 20’sF, the lower elevations below 2,000′ are cooling overnight to ~30F then warming into the 40-45F range. By late afternoon watch for the snow to become saturated and unsupportable, this is the sign to move to cooler aspects. Wet loose and wet slab avalanches are still possible at these lower elevations.

Cornices are large and likely hanging close to their tipping point. Direct sunshine, a person, or a group of people on top these could be enough to cause one to break. They can be extremely dangerous on their own, but with our current snowpack, they could trigger a large slab avalanche below, making a big problem even bigger. Give cornices a wide berth from above and limit exposure under them from below.