Avalanche Canada ghelgeson, Avalanche Canada

North Columbia Avalanche Forecast

Nov 24th, 2019 3:00PM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Storm Slabs and Persistent Slabs.

30+cm of snow with strong wind has left us with two problems: 

A potentially touchy storm slab.

A persistent slab that may remain sensitive to triggering.

Watch for signs of unstable snow and gather more info, especially if you're pushing beyond simple terrain.

Summary

Confidence

Low - Uncertainty is due to the limited number of field observations.

Weather Forecast

After a stormy weekend we’re transitioning to clearing skies, colder temperatures and no significant precipitation for the foreseeable future.

SUNDAY NIGHT: Freezing level dropping to Valley Bottom, light northwest wind, trace of snow possible.

MONDAY: Broken cloud cover, freezing level at valley bottom, light NW breeze, no significant precipitation expected.

TUESDAY: Broken cloud cover initially,scattered clouds in the afternoon, freezing level at valley bottom, light variable breeze, no significant precipitation expected.

WEDNESDAY: Clear skies at dawn building to scattered cloud cover in the afternoon, freezing level at valley bottom, moderate northeast wind, no significant precipitation expected.

Avalanche Summary

We're flying nearly blind here with very limited observations, but this MIN report from the neighboring Glacier National Park region helps to paint a picture of how touchy the storm slab problem was on Saturday. A natural size 2 storm slab was also observed in a north facing alpine feature near Revelstoke, but we suspect a much larger natural avalanche cycle occurred. If you were out Sunday please let us know what you're seeing by submitting to the MIN.

Snowpack Summary

Winter is slowly descending to the valleys with the snowline around 1200 m across the region. Total snowpack depths range from about 80 cm below treeline to as high as 180 cm in the alpine.  

The weekend storm produced 20 to 30 cm of snow accompanied by strong west/southwest wind. On steep south facing slopes in the alpine the new snow rests on a crust. A crust is also present on all aspects below 1600 m and many locations have surface hoar on top of the crust.

A problematic interface of surface hoar on top of a melt freeze crust can be found 50 to 100 cm below the surface. This "October Crust" is showing sudden & repeatable results when subjected to snowpack tests. Avalanches failing on this interface have the potential to be large and could easily surprise users who are getting out onto snow for the first time this season.

Problems

Storm Slabs

An icon showing Storm Slabs

Likelihood

Possible-Likely

Expected Size

1 - 2.5

The weekend storm produced 20 to 30 cm of snow accompanied by strong west/southwest wind forming widespread storm slabs. These slabs rest on a variety of weak layers which will likely keep them susceptible to human triggering Monday, especially in bigger terrain near ridge crest.

Aspects:

All aspects.

Elevations:

Alpine, Treeline.

Persistent Slabs

An icon showing Persistent Slabs

Likelihood

Unlikely-Possible

Expected Size

1.5 - 3

Crusts that formed in late October are now buried 50 to 90 cm deep. We're working off of a short list of observations, but this late October layer is highly variable and may be associated with both surface hoar and facets. This is a layer to test and watch over the next week as good visibility and travel begin to sing the Alpine's siren song.

Aspects:

All aspects.

Elevations:

Alpine, Treeline.

Valid until: Nov 25th, 2019 5:00PM