Avalanche Forecast
Issued: Mar 12th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Loose Wet, Cornices and Persistent Slabs.
ghelgeson,
Avalanche Canada
We're looking at a sunny & warm weekend which will destabilize the snowpack throughout the region. Cornice failures and loose wet avalanches are expected to be widespread, and there is potential for larger avalanches to fail naturally during periods of peak warming.
Summary
Confidence
Weather Forecast
It looks like this will be the weekend where the weather really transitions from winter to spring.
FRIDAY NIGHT: Freezing level holding around 1500 m, strong southwest wind, trace of snow in most locations but Mackenzie and the Pine Pass could see 10 to 15 cm of snow at upper elevations with rain at valley bottom.
SATURDAY: Scattered cloud cover, freezing level climbing to about 2100 m, strong southwest wind, no significant precipitation expected. Very little overnight refreeze expected Saturday night.
SUNDAY: Scattered cloud cover, freezing level holding between 2000 and 2500 m, strong southwest wind, no significant precipitation expected. Freezing level returning to valley bottom Sunday night.
MONDAY: A few clouds, freezing level rising to 2000 m, moderate southwest wind, no significant precipitation expected.
Avalanche Summary
The rising freezing level this weekend may induce a natural avalanche cycle as the snow is destabilized by warming temperatures. Some natural cornice failure was noted on Thursday which is likely a portent of things to come. Our field team found some large and disturbingly wide avalanches in the Hasler Tuesday, lots of compelling images in their MIN report here. It's suspected that these are running on facets that are about 80 cm below the surface.
This adds to the tally of recent large avalanches they started collecting in Pine Pass on Monday. All of this activity leaves me feeling uneasy about a big warm up this weekend.
Snowpack Summary
The dramatic rise in temperature this weekend is going to be a good test for our snowpack. Wind effect is widespread in the alpine and treeline across the region and solar aspects currently sport a sun crust. The north of the region around Pine Pass picked up almost 15 cm of new snow Thursday night, but very little new snow has fallen recently in the rest of the region.
About a metre of snow covers a weak layer of facets buried mid-February. Slightly deeper there is a widespread persistent weak layer from late January/early February that consists of surface hoar. It is most prevalent around treeline elevations, but likely reaches into the alpine and in openings below treeline too. These layers are both significantly shallower in the east of the region.
Terrain and Travel
- Avoid avalanche terrain during periods of strong sun.
- A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
- Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
- The more the snowpack warms-up and weakens, the more conservative you`ll want to be with your terrain selection.
Problems
Loose Wet
Potentially large loose wet avalanches are likely Saturday afternoon, especially on steep solar aspects.
Aspects: East, South East, South, South West, West.
Elevations: All elevations.
Likelihood
Expected Size
Cornices
Cornice failure is likely this weekend as the strong mid-March sun and warming temperatures go to work. As cornices impact underlying slopes there is potential for them to trigger persistent slab avalanches.
Aspects: All aspects.
Elevations: Alpine.
Likelihood
Expected Size
Persistent Slabs
The persistent slab problem appears to have been put to rest in deep snowpack areas in the west of the region, but on the eastern slopes (e.g. Kakwa/Tumbler Ridge) there have been very large recent natural avalanches. The rising freezing level this weekend may wake this problem up. The most likely triggers are surface avalanches stepping down, cornice fall, or the weight of a machine or a person hitting a thin-spot.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Mar 13th, 2021 4:00PM
