Avalanche Forecast
Issued: Dec 18th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs, Loose Dry and Deep Persistent Slabs.
Conrad Janzen,
A storm starting Friday night will increase the hazard. The Moderate rating below treeline is due to the potential for avalanches triggered at upper elevations to run full path in steep terrain. Minimize overhead hazard for the next few days!
Summary
Weather Forecast
Strong to extreme west winds and 5-15 cm of new snow are forecast starting Friday night with snowfall tapering off by Saturday morning. Less snow is expected Eastern and Southern areas but winds will still be very strong. Valley bottom temperatures should stay around -5 with ridge top temperatures around -12 to -16.
Snowpack Summary
Cornices growing and wind slabs forming in the alpine with moderate to strong W winds. 20-50 cm of storm snow at treeline sits over the Dec 13 and Dec 7 layers of sun crust, facets and some surface hoar. The Nov crust/facets exist near the bottom of the snowpack and are weakest in shallow snowpack areas. Snowpack at treeline is between 80-160 cm.
Avalanche Summary
Ski resorts again reported small ski-cut and explosive triggered wind slabs and a couple loose dry avalanches in the alpine up to size 1.5 on Friday. Only a couple small loose dry natural avalanches in steep cliffs were observed.
Confidence
Intensity of incoming weather systems is uncertain on Saturday
Problems
Wind Slabs
Widespread wind slabs are expected in the alpine and down into treeline with arrival of strong winds and new snow Friday night. In steep avalanche paths and gullies these have the potential to run down below treeline.
- Minimize overhead exposure during periods of heavy loading from wind.
- Choose ice climbs that are not exposed to avalanches from above.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Loose Dry
The strong winds and new snow will likely cause loose dry avalanches in steep gullies and on steep faces over the weekend. These avalanches will be smaller but could run a long ways in the recent storm snow.
- Be cautious with gully features.
- Be careful of loose dry power sluffing in steep terrain.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
The Nov 5 crust has facets above and below it and exists up to 2500m on shady aspects and higher on solar aspects. We have limited observations of deep slab avalanches recently but increasing wind and snow over the next three days may change this.
- Pay attention to overhead hazards like cornices which could trigger the deep persistent slab.
- Be aware of thin areas that may propogate to deeper instabilites.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 19th, 2020 4:00PM
