Avalanche Forecast
Issued: Dec 26th, 2020 4:13PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs, Persistent Slabs and Deep Persistent Slabs.
Tim Haggarty,
While more settled weather is on the way, recent winds and snowfall have left a complex snowpack that features a great deal of variability and multiple weak layers.
There is a Special Avalanche Warning in effect. Click Here to access.
Happy Holidays!
Summary
Weather Forecast
After continued light snowfall favoring the northern part of the region, expect some short-lived clearing on Sunday as a ridge develops. Weak disturbances may bring trace amounts of snow Monday and cloud. Alpine winds will remain light out of the west and temperatures near -10C.
Snowpack Summary
Small amounts of new snow now bury wind slabs created by recent 25-45km/hr SW-W winds redistributing the 30-60cm of snow from the past week. The Dec 13 and Dec 7 sun crust/surface hoar/facet layers are down ~ 50cm and ~80 cm respectively. The decomposing Nov crust/facets sits at the bottom of the snowpack. Height of snow at tree line is 120-170cm.
Avalanche Summary
Four days of avalanche control earlier this week produced mixed results, from no result to size 3.0. Most were storm slabs, sometimes stepping down to persistent layers. No new reports or observations today however visibility was limited by snowfall.
Confidence
Due to the number of field observations
Problems
Wind Slabs
Wind slabs were formed by strong SW-W winds Wednesday through Friday. While these are becoming buried with new snow, expect to find small, spotty slabs as you enter open areas at Tree Line and to encounter more developed slabs and in the Alpine.
- Watch for shooting cracks or stiffer feeling snow. Avoid areas that appear wind loaded.
- If triggered the wind slabs may step down to deeper layers resulting in large avalanches.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
There are a variety of weaker layers down ~50-80cm. These are the Dec 7 and 13th layers of facets, suncrust, and isolated surface hoar. These layers deserve constant suspicion: they can change quickly from one aspect or elevation to another.
- Dig down to find and test weak layers before committing to a line.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
We have had a few observations of avalanches stepping down to the Nov. 5 crust and facets. This is a problem with higher uncertainty, and is most prevalent in shallow snowpack areas where the layer has weakened over time.
- Be cautious in shallow snowpack areas where triggering is more likely.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 27th, 2020 4:00PM
