Turnagain Pass

Above 2000′ where the rain crusts disappear the layer of surface hoar that was buried by the mid February storms is lingering as a concern in the advisory area. Relatively calm weather has been over the region for a few days now. This has allowed for folks to push further into the mountains with no reports of avalanche activity since last Saturday. However, this weekend it is important remember that poor snowpack structure still exists with this thin layer of buried surface hoar sitting 2-3′ below the surface and the slab is large enough that the consequences could be high if you find the wrong spot. Triggering an avalanche breaking on this layer is becoming tougher by the day as the snowpack slowly stabilizes and adjusts but the possibility shouldn’t be forgotten. 

The most likely place to find one of these larger slides is on steep slopes with thin areas and rock bands. Trigger points are often these thin areas, near rocks and zones that may have been scoured slightly by winds. Also, these slabs can break above you, and release after several tracks are on a slope. Be aware that snow pits and stability tests may not be representative of the actual slope you are trying to assess. A helpful way to think about this problem is to consider the consequences of a slope if it slides and identify and avoid terrain traps (gullies, cliffs, or trees below).

Deep Persistent Slab: Various layers of weak faceted snow sits at the bottom of the pack in certain areas. In the Summit Lake zone and some areas in Girdwood Valley and towards the southern end of Turnagain near Johnson Pass depth hoar has been found. Similar to the problem above, these layers will be very tough to trigger, but a possibility remains in places with this structure. 

Snow pit profile from Sunburst on Tuesday. Note the structure: buried surface hoar sandwiched below a stiff slab and stiff potential bed surface.

Snow pit on Thursday showed similar stucture across the road on Seattle Ridge.  In both locations tests showed that the layer was harder to trigger but still a possibility.

Wind slabs: Loose surface snow combined with W-NW ridgetop winds in the 10-20 mph range gusting into the 30s overnight may have formed shallow wind slabs on leeward features. The snow may feel “upside down” with slightly stiffer snow over softer snow. Look for areas of pillowed or drifted snow and identify steep features like convexities or gullies where the snow may be more loaded.  Blowing snow and shooting cracks will be obvious clues to look for today. 

Loose snow avalanches: The top 6” of surface snow is loose and sluffs may be easy to initiate and fast moving on steep terrain features protected from the winds. 

Cornices: Remember these unpredictable hazards can break farther back onto a ridge than expected and have the potential to trigger an avalanche on the slope below. Give cornices extra space and avoid being under them. 

Glide avalanches: There is a new glide crack above the flats along Seattle Ridge, just looker’s left of the up-track and Repeat Offender slide path. Avoid hanging out under this crack and any others you may see – these release without warning and are very destructive.

Sunshine: Today skies may be be partly sunny and solar warming may trigger loose snow avalanches in steep Southerly aspects. 

Wind effect just South of Pyramid Peak on Thursday.