Avalanche Forecast

Archived

Nov 24th, 2019–Nov 25th, 2019

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

North Columbia.

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.

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

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.