Avalanche Forecast
Issued: Feb 24th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
JSmith,
Avalanche Canada
New snow and wind are expected to form fresh storm slabs throughout the day that will be most reactive in wind affected terrain. Pay attention to changing conditions with elevation and aspect.
Summary
Confidence
Weather Forecast
WEDNESDAY NIGHT: Cloudy with flurries; 3-5 cm. / Strong, southwest ridgetop wind / Alpine low -14 / Freezing level valley bottom.
THURSDAY: Snow; 10-15 cm, with another 3-10 cm. overnight / Strong, west ridgetop wind / Alpine high -4 / Freezing level 1100 m.
FRIDAY: Mostly cloudy / Light, northwest ridgetop wind / Alpine high -3 / Freezing level 1200 m.
SATURDAY: Mix of sun and cloud / Moderate, northwest ridgetop wind / Alpine high -4 / Freezing level 1100 m.
Avalanche Summary
On Tuesday, explosive control work on Kootenay Pass produced numerous wind slabs up to size 2.5 on primarily south aspects, with crowns up to 100 cm. in wind loaded features.
There were many reports of human triggered persistent slab avalanches during the first two weeks of February. These avalanches failed on a surface hoar layer that is now 50-100 cm deep and is most prevalent at treeline elevations. There were also two very large explosive triggered avalanches in the Bonningtons in the past month that stepped down to the early December crust (most recently on Feb 9). These deeper instabilities have been trending towards being unreactive, however occasional snowpack tests suggest they may still be possible to trigger in isolated areas.
Snowpack Summary
Weak surface hoar sitting on a crust on solar aspects has been reported in the Kootenay Pass area. This layer may also be present in other areas within the region. Storm slabs formed by incoming snow and wind Thursday will be more sensitive to human triggering in areas where this weak layer was preserved before being buried; especially if the surface hoar is sitting on a crust.
25-50 cm of recent snow and strong southwest winds have formed reactive wind slabs on lee and cross loaded features at treeline and above.
The main persistent layer of concern below the surface is a combination of surface hoar, facet, and crust layers that formed in January that are now buried 60-150 cm. deep. Steep, open slopes at treeline elevations are the most likely spots to trigger a large avalanche on this layer.
Terrain and Travel
- Be careful as you transition into wind affected terrain.
- Avoid lee and cross-loaded terrain.
- Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
Problems
Storm Slabs
New snow and wind are expected to form storm slabs throughout the day that will be most reactive in wind affected terrain.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
A persistent weak layer 50-100 cm deep continues to show reactivity in snowpack tests, despite not producing avalanches in the past week. This surface hoar/crust interface may remain human triggerable in steep convex features at treeline and potentially steep alpine features where it presents as a crust.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 25th, 2021 4:00PM
