Turnagain Pass

It has been over a week since the last loading event placed 2-3’ slabs on top of a layer of surface hoar.  This layer was evenly distributed on Turnagain Pass from 1,500’ up to ridge tops.  Soon after this loading event a large avalanche was triggered by a skier resulting in a burial (and recovery).  Since that time we have not seen or received reports of any further avalanche activity.  

Despite the lack of activity, we are still left with a layer that is not trustworthy.  This layer of buried surface hoar has gained strength over the past week.  As it has gained strength it has also become more difficult to detect in our pits.  We are still finding it and it continues to show potential for propagation across slopes.  Add into the mix a slab that’s become more dense over time.  This slab is generally 2 feet thick in starting zones and has the ability to support a lot of weight.  While this may sound like a good thing, it can also be misleading in that you might be able to put many tracks on a slope without triggering an avalanche.  What our tests have shown, however, is that if you find the right trigger point and are able to initiate an avalanche, the outcome could be bad, as this slab + weak layer combo has the potential to produce high volume (relative to humans) avalanches.

During the last storm rain fell in the middle of the event which has now become a buried crust up to 2,500’ in elevation.  This rain and resulting crust has destroyed the buried surface hoar in the lower portion of the treeline elevations and added some strength to the slab in the upper portions of this elevation band.

What does this all boil down to?  Avoid steep terrain and trigger points above 2,500’.  Slopes over 35 degrees, convex rollovers, and areas where the snowpack is thinner are places where you could trigger an avalanche today.  Obvious signs like shooting cracks or whoompfing may or may not present themselves– this problem is better understood through investigating the snow below the surface.  Conservative terrain selection is the best way to manage this problem and have an enjoyable Christmas Day.

Winds have picked up this morning along ridge tops with Seattle ridge showing wind speeds in the 25 mph range.  4-6” of low density snow sitting on the surface combined with the potential for another 5” to fall during the day could produce pockets of wind slab up to 10” in depth.  Due to the showery nature of the current local weather pattern, this will be a greater issue in areas receiving those 5”.  Be on the lookout for wind loading along ridge crests and in upper elevation starting zones.  Predominant wind direction will be out of the East and Southeast but know that wind direction will vary as wind interacts with terrain.  Pay attention to and avoid slopes that are actively being loaded by wind, have a rounded and pillowy look or produce shooting cracks as you step onto them.