Storm Slabs and Persistent Slabs

Location Name: 
Storm Slabs and Persistent Slabs
Williams Lake Area
Date and time of observation: 
Wed, 02/05/2020 - 11:36

Red Flags: 
Recent avalanche activity
Whumphing noises, shooting cracks, or collapsing
Obvious avalanche path

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

Lots of snow out there with storm totals at 15 to 20" of snow with about 1.35 to 1.5" of snow water equivalent (SWE).  There was evidence of natural storm slab avalanches that ran sometime during the storm on all aspects, especially steeper terrain greater than 38 degrees.  Avalanches were confined to near and above treeline.  We did have an obvious natural avalanche on a ENE aspect that started up high and stepped down into deeper faceted weak layers (See Photos) 

Our faceted weak layers are stressed with the rapid load of nearly 1.5" of water.  Weak layers that were taken hard force to initiate failure are failing under easy force with this new load.  Our strong sun here at this low latitude was enough to start loose snow avalanches on steep southerly aspects during the day.  

Northwest winds over night were enough to transport the new snow into soft but stiffening slabs near and above treeline.

Photo 1: Natural Storm Slab avalanche that stepped down into deeper faceted weak layers on a ENE aspect

Photo 2: Loose snow avalanches on southerly aspects

Photo 3: Winds were strong enough to stiffen the new snow above treeline into breakable wind crusts above treeline

Photo 4: Crown profile where the natural avalanche stepped down into deeper faceted layers

Photo 5: Snowpit on a ENE aspect at 11,500'

Snowpack photos: 
Weather Observations
Blowing Snow: 
Cloud Cover: 
25% of the sky covered by clouds
Air temperature: 
Below Freezing
Wind Speed: 
Air temperature trend: 
Wind Direction: 
Accumulation rate: 
More detailed information about the weather: 

Very cold start to the morning with temperatures well below 0 F at all elevations.  Temperatures quickly warmed during the day making it to the single digits above 10,500' and into 20's at 9000'.  Lots of sun that felt bright with all the new snow.  Winds were calm below 5 MPH during the day.