Avalanche Forecast
Issued: Feb 20th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs, Deep Persistent Slabs and Persistent Slabs.
isnowsell,
Avalanche Canada
Ongoing snow and wind have created very dangerous avalanche conditions. Natural avalanches are possible and if deep persistent layers are released could create very large destructive avalanches.
Summary
Confidence
Moderate
Avalanche Summary
On Saturday a large (size 2.5), natural avalanche was reported from the far north of the region. It was initiated as a wind slab near ridgetop, before stepping down to basal facets and ground.
A couple of wind slab avalanches were also reported over the weekend throughout the region, in steep alpine terrain.
On Friday, our field team observed a size 3.5 avalanche in the Bull River area (South Rockies) on an east through southeast aspect that started high and ran nearly 2000 m to the river. They estimated this avalanche to likely have occurred on or around February 15. Given its size, this avalanche likely failed on a deep persistent weakness in the snowpack.
On Thursday, a size 3.5 avalanche failed on a deep persistent weakness, resulting in 2 fatalities west of Golden.
Snowpack Summary
New snow over the long weekend has buried a layer of surface hoar that formed in open areas and a sun crust that exists on steep south aspects. In exposed terrain, recently formed wind slabs exist in leeward features.
A variety of persistent layers still exists in the middle snowpack and continue to see avalanches occur on them periodically. Don't let these layers surprise you.
The lower snowpack contains a widespread layer of large, weak facets that is typically 80 to 150 cm deep. This layer continues to periodically produce very large and destructive avalanches.
Snowpack depths at treeline range between 80 and 200 cm, with the shallowest snowpacks found on the eastern edge of the Purcells.
Weather Summary
Monday night
Cloudy with snow, 10 to 20 cm. Moderate southwest alpine winds, switching to the northeast by Tuesday morning. Treeline temperatures -5 to -10 C.
Tuesday
Cloudy with sunny periods and flurries, 5 to 15 cm. Moderate northeast alpine wind. Treeline temperature around -10 C, dropping to -20 C by end of the day.
Wednesday
A mix of sun and cloud, with no precipitation. Moderate northeast alpine winds. Treeline temperatures -20 to -25 C.
Thursday
A mix of sun and cloud, with no precipitation. Moderate northeast alpine winds. Treeline temperatures -20 to -30 C.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Storm slabs in motion may step down to deeper layers resulting in large avalanches.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Choose low-angled, sheltered terrain where new snow hasn't been wind-affected.
- Avoid rock outcroppings, convexities, and anywhere the snowpack is thin and/or variable.
Problems
Storm Slabs
Ongoing snow and wind on Monday night and Tuesday will produce reactive storm slabs and wind slabs. Expect to find touchy avalanche conditions in wind exposed terrain that receive more then just a few centimeters of snow.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Deep Persistent Slabs
The bottom of the snowpack consists of large, weak basal facets. Large, deep avalanches are most likely to be triggered in shallow areas with variable snow depths.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A number of weak layers of surface hoar remain a concern in the mid and lower snowpack.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 21st, 2023 4:00PM
