Wind and Persistent Slab

Location Name: 
Wind and Persistent Slab
Region: 
Williams Lake Area
Date and time of observation: 
Thu, 03/02/2017 - 22:26
Location Map: 
United States
36° 33' 3.0636" N, 105° 26' 11.9364" W
US


Red Flags: 
Recent avalanche activity
Recent loading by new snow, wind, or rain
Obvious avalanche path

Observation made by: Forecaster
Snowpit Observations
More detailed information about the snowpack: 

Finally made it into the alpine to check out what's going on.  It's not the easiest with the bottom up approaches!  A warm day with the southern latitude sun.  I suspect we'll have sun crusts on solar aspects tomorrow even though temperatures remained cool today.  Winds died down from overnight but there was wind effected snow in the alpine.  A north aspect pit near treeline confirmed what we were seeing on Tuesday with the storm.  Monday mornings snow that came in as lower density was covered by a little over two feet of storm slab. This layer is still a concern and will be a concern for a while longer.  Getting up onto Lake Fork proper there was a freshly formed wind slab that was obvious.  This 4 Finger wind slab was easy to trigger and obvious.  It was a small wind slab but ran a considerable distance considering it was only 10" thick.  In a snowpit on Lake Fork on NNE aspect we found 4' of slab ranging from F to 1F with 4" of lower density snow below it.  We were able to initiate collapse and propagation with an ECTP 20 SP 110cm down and a PST 25/110 END SC.  

Scary snowpack right now that is hard to trust on North and East Aspects especially above treeline.  This layer is what we've seen a lot of things run on Tuesday.  There was evidence of numerous naturals more than likely on Tuesday although some from Wednesday were also observed (No snow covering up the crowns or debris). A lot of these naturals were below rock bands.  A 4 to 5 foot slab on top of a very weak layer that is sitting on a firm crust is no joke. The consequences will be huge.  The small wind slab that was triggered did not step down onto that weak layer 4 feet down. Another concern is that although the weak layer is 3 to 5 feet down it is not a hard slab that is insulating it from a skiers weight.  We're back to worrying about trigger points and where the slab is thin and you might be able to impact that weak layer.  It might be ten turns in or you might get away with it!  But as we've seen from this cycle is that the potential is there for these avalanches to be large and destructive.    

Photo 1: Snowpit from Lake Fork on a NNE Aspect.  Wind Slab about 10" thick with buried near surface facets below. ECTP 1 SC on the wind slab.  This was pretty easy to trigger.  110cm down is the lower density snow that fell on Monday.  ECTP 20 SP and PST 25/110 END SC.  

Photo 2: Wind Slab that I triggered on purpose.  No one was below.

Photo 3: The wind slab before I ski cut it.  Notice the obvious pillow!

Photo 4: North Aspect pit dug Near Treeline.  The low density snow from Monday morning is 92cm down and we were able to initiate collapse and propogation with an ECTP 15 SP.

Photo 5: Graham's skin track from yesterday is slighly blown in from the wind overnight.

Video 1:  Explaining the wind and persistent slab problem that we are dealing with!

 

Snowpack photos: 
Snowpit videos (tests, etc): 

Wind and Persistent Slabs in the Alpine

Weather Observations
Blowing Snow: 
No
Cloud Cover: 
Clear
Air temperature: 
Below Freezing
Wind Speed: 
Calm
Precipitation: 
None
Air temperature trend: 
Warming
Wind Direction: 
West
Accumulation rate: 
More detailed information about the weather: