Avalanche Forecast
Issued: Dec 17th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
swerner,
Avalanche Canada
Watch out for wind slabs they're likely reactive to human triggers at upper elevations. Choose conservative terrain and watch for signs of instability such as whumphing, cracking and recent avalanches.
Summary
Confidence
Low - Uncertainty is due to the limited number of field observations.
Weather Forecast
Friday: Snow amounts 5cm with alpine temperatures near -7. Ridgetop wind strong-extreme from the southwest and freezing levels valley bottom.
Saturday: Snow 5-10 cm with alpine temperatures near -7. Strong-extreme wind from the West and freezing levels 1000-1500 m.Â
Sunday: Snow amounts 10-20 cm. Alpine temperatures -1 and freezing levels 2000 m. Extreme 65-105Km/hr wind from the southwest.
Avalanche Summary
No new reports on Thursday. Avalanche control using explosives in the Lizard range produced several slabs up to size 2 in alpine terrain and a size 1.5 in treeline terrain. This may indicate that slabs may be sensitive to human triggers on Friday.
Please consider sharing your observations on the Mountain Information Network. Thank you to those that have already submitted this winter.
Snowpack Summary
Up to 20 cm of new snow and strong to extreme southwest wind have likely formed reactive wind slabs at treeline and in the alpine. The recent snow brings 30-50 cm above the early December crust which exists in the snowpack up to 2000 m. Use caution if you find cohesive snow above the crust, particularly if there are weak, sugary faceted grains immediately above or below the crust. With slab cohesion adding stress and load on that interface we may see this persistent slab avalanche problem come to life.
The snowpack depth varies substantially in the region and has been described as thin, wind-hammered, variable, and tapering rapidly at lower elevations. The average snowpack depth at treeline is approximately 100 cm.Â
The middle of the snowpack has been reported as being well-consolidated and may host another hard melt-freeze crust.
The base of the snowpack consists of a hard melt-freeze crust from early-November that may have faceted grains around it. There has not been recent avalanche activity on this layer but it remains on our radar. The most likely spot to trigger it would be on thin and rocky slopes.
Terrain and Travel
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
- Avoid areas where the snow feels stiff and/or slabby.
Problems
Wind Slabs
Strong southwest wind is forecast for the rest of the week along with a bit of new snow. Use caution near ridges and avoid leeward slopes, particularly where you find stiff wind affected snow. Loose-dry sluffing from steep terrain features.
Aspects: North, North East, East, South East, South, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
30-50 cm of snow currently sits above a buried crust from early December. Sugary, facets above and/or below the crust may weaken the bond and the persistent slab may become reactive, especially to human triggers.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 18th, 2020 4:00PM
