Avalanche Cycle Above Treeline on North Aspects

Location Name: 
Williams Lake Drainage
Region: 
Williams Lake Area
Date and time of observation: 
Sun, 12/01/2019 - 13:55
Location Map: 
United States
36° 32' 28.5936" N, 105° 25' 49.0656" W
US


Red Flags: 
Recent avalanche activity

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

We took advantage of the better visibility to assess the avalanche cycle from Friday evening or early Saturday morning.  The avalanche cycle was mainly confined to North aspects above treeline that was running on basal facets near the ground.  This weak layer was from the October snow that remained during the three weeks of high pressure in November and faceted into 1 to 3mm facets. North aspects from Sin Nombre, Vallecito, Lake Fork and Kachina all ran naturally.  Most were small size 1 avalanches with a couple of bigger size 2 avalanches.  There were a lot of mid path crowns from strong winds transporting snow further down off of ridgetops. Were we had connectivity we had wider propagation like we saw on Sin Nombre.

  

Above Treeline:

The strong WSW winds from 11/29 and 11/30 stripped most south and west aspects on the windward side to bare ground in many places.  North and East aspects above treeline have the deepest snowpacks right now and saw some loading but with such strong winds gusting in the 80's most of this snow sublimated into the air.  Areas above treeline have hard (pencil to knife) slabs of varying depths. Many areas have multiple wind slabs that formed in the last week from different wind events.    

Near Treeline:

Near treeline is where we are finding a more evenly distrubuted snowpack in the 80 to 100cm range.  Softer supportable slabs were found in these areas.  We did not notice any major avalanche activity here except for steep convex rolls on north aspects.  North aspects near treeline still have a poor snowpack structure with a 4F to 1F slab resting on top of basal facets. 

Below Treeline:

These areas are still thin with 30 to 40 cm snowpack on south and west aspects and a slightly deeper snowpack on north and east aspects.  There were a lot of blow downs during the storm.  On Sunday with a warming trend solar aspects were taking heat.   

Photo 1:  Crown roughly drawn in below the rock band on Sin Nombre.  Always another crown on the convex roll lower down.

Photo 2: Closer in photo of the crowns on Sin Nombre

Photo 3:  One of the crowns on Sin Nombre.  

Photo 4: Stripped W and SW slopes from the top of Lake Fork with NE slopes holding more snow

Photo 5:  Near treeline on a North aspect where we did not see avalanches still has basal facets

 

Snowpack photos: 
Weather Observations
Blowing Snow: 
No
Cloud Cover: 
25% of the sky covered by clouds
Air temperature: 
Below Freezing
Wind Speed: 
Light
Precipitation: 
None
Air temperature trend: 
Warming
Wind Direction: 
West
Accumulation rate: 
None
More detailed information about the weather: 

Sunny morning before high clouds moving in during the afternoon.  Temperatures started off in the teens and quickly rose throughout the day with temperatures remaining below freezing above 9000'. West winds were light during the day below ridgetops with winds in the teens at the ridgetops with no significant blowing snow.