Turnagain Pass

Yesterday definitely saw somewhat of a wind slab avalanche cycle, particularly in the southern end of the advisory area where there is generally a shallower and poorer snowpack structure.  Observations from Lynx Creek found several shallow but very well connected fresh wind slabs.  Though nothing we saw yesterday was super deep (12-18”), many of these slabs were in consequential terrain if a skier or snowmachiner were caught.  It’s important to keep terrain choices in mind with a problem such as this.  Though a 12” wind slab may not scream ‘deadly avalanche’ it is enough to knock you off your feet or push you into a terrain trap, compounding consequences.

Slabs were observed on all aspects yesterday so it’ll be important to suss out any wind-loaded terrain today by paying attention to the surface – shooting cracks, whumphing, textured surface or hollow sounding and drum-like snow are all clues that a wind slab is present.  These are likely to be moderate to easy to trigger again today.  The predominant Northwest flow we saw Monday night tends to be channeled through Turnagain Pass, such that Southerly winds are seen on the East side (non-motorized) of the highway – loading Northerly slopes.  Not intuitive, but mountain weather is complex!  Bottom line is that these wind slabs may be found on all aspects of the compass today.

Fresh wind slab on the west shoulder of Captian’s Chair, above Lynx Creek.  This was one of many slabs observed in this area yesterday.

Wind textured surface on an East facing slope, above Lynx Creek.

Cornices:  These backcountry bombs are still ripening and can be quite unpredictable this time of year.  Cornices have a tendency to break farther back along ridgelines than expected and have the potential to trigger an avalanche on the slope below. Give them extra space and avoid spending time under them. 

Monday/Tuesday winds were likely enough to overload the February 9^th buried surface hoar layers on the southern end of the advisory area.  This layer has been found to be quite a bit shallower (12 – 20” deep) on the southern end of Turnagain Pass, making it easier to trigger.  In areas with a deeper overall snowpack (Seattle ridge, Tin Can, Sunburst, Girdwood Valley) we are still finding this persistent weak layer and although it is becoming tougher to trigger, it does continue to show the potential to fail and propagate. 

With the addition of wind loading, the Feb. 9^th buried surface hoar could be closer to a tipping point potentially creating a larger slab avalanche 2-3’ thick.  Likely trigger spots are in places where the snowpack is thinner – near rock bands or on more scoured features. These slabs can break above you, and release after several tracks are on a slope. Be aware that no red flags may be present.

Deep Persistent Slab: We continue to find various layers of weak faceted snow and depth hoar near the bottom of the pack in certain areas. This includes Summit Lake zone, and some areas in Girdwood Valley and towards the Southern end of Turnagain pass, near Johnson Pass and Lynx Creek. Similar to the problem above, these layers will be very tough to trigger, but a possibility remains in places with this poor structure.

Glide avalanches:  The glide crack just looker’s left of the Seattle ridge up-track was blown over and mostly filled in yesterday. It is still discernable and appears to be slowly opening.  Avoid hanging out under this crack and any others you may see, as they are very destructive and unpredictable.  #lowprobabilityhighconsequence