Turnagain Pass Avalanche Forecast

Snow does not like rapid change.  When rapid change occurs, weak layers have a hard time adjusting to the load.  Winds overnight have brought about this rapid change.  Slabs have been actively growing on leeward slopes in the higher elevations.  Winds have been mainly out of the East.  The important thing to remember about wind is that direction changes are common in mountainous terrain.  With that said, recognition of wind loaded slopes is a better assessment tool than reading the weather station data when it comes to wind direction and loading patterns.

Shooting cracks and collapsing are obvious indicators of unstable slabs.  Stiff, hollow and upside snow should be avoided today in leeward starting zones and cross loaded terrain features.  These slabs could build into the 12” range and have enough volume to injure or bury a person.

A layer of weak faceted snow sits anywhere from 2-16” below the surface.  This layer is widespread throughout the forecast area.  This layer is deepest on the North end of Turnagain Pass (Eddies, Pyramid) where snowfall earlier in the week put down slabs up to 12” thick.  Heading South along the Pass that slab gradually gets thinner and less continuous across slopes with averages in the 6-8” range.  As a result we have seen more reactive snow where that slab is thicker, including remotely triggered avalanches within the last 2 days.  In the Girdwood Valley we have a different setup, where older dense wind slabs 4-8” thick that formed a week ago are sitting on this weak layer and concealed by 6″ of snow that has fallen this week.  

To put it simply, we have the perfect recipe for a slab avalanche in many areas today; slab + weak layer.  Add into the mix the right terrain (slopes 35 degrees and greater) and a trigger (humans or rapid loading of snow) and the result is avalanches.  

Avalanches could occur within newly formed wind slabs and they could also step down to this weak layer.  Regardless of the actual failure layer, it will be important to avoid slopes 35 degrees and over that have this slab/weak layer combo.

A continuation of above freezing temperatures in the mid elevations along with occasional rain will make wet loose avalanches another concern today.  Volume of these will be generally low.  Despite this it will be important to recognize and avoid steep terrain that is holding loose, weak and damp snow.  This snowpack issue becomes more concerning when traveling above terrain traps such as cliffs, gullies and trees.