Persistent Slabs on North Aspects

Location Name: 
Persistent Slabs on North Aspects
Region: 
Williams Lake Area
Date and time of observation: 
Sat, 01/27/2018 - 12:30


Red Flags: 
Whumphing noises, shooting cracks, or collapsing
Recent loading by new snow, wind, or rain
Obvious avalanche path

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

Strong WSW winds yesterday (Gusting 70 MPH) have left a hard pencil hard slab above treeline that is capping our snow from Sunday (1/21) . In other places the strong winds have scoured back to bare ground and further in others has left breakable wind crust.  Not great conditions to make a turn!  We are still experiencing loud collapsing whumpfing on north aspects above treeline.  Pretty much every slope we touched on a north aspect collapsed with shooting cracks well above us.  This is where we have a variable but poor snowpack structure with fragile depth hoar near the ground that is capped by some form of slabs.  We continue to see evidence of a natural avalanche cycle that occurred during the storm on Sunday 1/21.   We have two types of persistent slab problems that can be seen in the first two photos.  Both are a result of depth hoar near the ground but one is more obvious than the other.  Areas that had a deeper snowpack before last Sunday's storm holds the potential for a larger deeper avalanche where snow from November has lingered and is capped by several slab weak layer combinations.  This is harder to identify as the persistent weak layers are further down from the surface.  The other persistent slab problem is where last Sundays snow fell on faceted depth hoar on the ground.  Although triggering an avalanche is getting harder and harder, there's a very real spooky feeling when traveling on north aspects above treeline. Either way you slice it, all the ingredients are there for an avalanche breaking on or near the ground.  Here's a video from today!  

Other aspects are not as worrisome, and we are getting sun crusts on solar aspects and are quickly seeing our snowpack settle at lower elevations.  The extant of the wind loading and producing a wind slab seems to be limited to above treeline and areas near treeline that are open and prone to wind loading.  

Photo 1: A deeper snowpack where snow from November still lingered from previous wind loading events.  This slope collapsed with shooting cracks well above us.  

Photo 2:  A shallower snowpack that also collapsed with shooting cracks.

Photo 3: Scoured back the ground at Williams Lake with Lake Fork getting loaded from the WSW winds on 1/26

Photo 4:  Breakable wind slab that is miserable to skin in and ski!

Snowpit or crown profile photo or graph: 
Snowpack photos: 
Weather Observations
Blowing Snow: 
No
Cloud Cover: 
25% of the sky covered by clouds
Air temperature: 
Below Freezing
Wind Speed: 
Light
Air temperature trend: 
Warming
Wind Direction: 
Southwest