Avalanche Forecast

Issued: Mar 5th, 2020 5:00PM

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

Avalanche Canada astclair, Avalanche Canada

Email

It's complicated: 1) fresh snow may disguise reactive wind slabs; 2) a widespread, touchy weak layer may just be waiting for a trigger; 3) clearing skies in the afternoon could ramp up reactivity.

Avalanches have been large and human triggering remains likely at all elevations.

Summary

Confidence

High -

Weather Forecast

Thursday night: Cloudy, convective flurries with up to 5 cm of snow, moderate southwest winds, alpine temperature -6 C, freezing level 1000 m.

Friday: Cloudy, 5-15 cm of snow, light southwest winds, alpine high temperature -2 C, freezing level 1400 m.

Saturday: Cloudy, 5-10 cm of snow, light variable wind, alpine high temperature -1 C, freezing level 600 m.

Sunday: Decreasing cloud, isolated flurries with up to 5 cm of snow, light west winds, alpine high temperature -3 C, freezing level 800 m.

Avalanche Summary

Over past 48 hours, a natural wind slab avalanche cycle was observed. These avalanches were small to very large (size 1-3) breaking 20-60 cm deep on leeward features at upper elevations. Several were triggered by cornice falls.

There has been a flood of reports of avalanches releasing on the February 22 surface hoar since Saturday. Both skier-triggered and remotely-triggered avalanches have been reported by nearly every operation region-wide, even as professionals tiptoe around and avoid suspect terrain features. The problem is touchy but tricky. In many instances, slopes were ski cut with no results, only to have the third or fourth skier in the group trigger the slab. 

Avalanche size has increased since the weekend, with more of the activity releasing size 2+. Observations extend to all aspects and elevations, but north to east aspects near treeline have been a hot-spot for reactivity. Avalanches are also occurring at unusually high elevations for surface hoar, with several cases of wind slabs stepping down in the alpine.

Snowpack Summary

Incremental snowfall and recent strong winds formed reactive wind slabs in the alpine and open areas at treeline that remain likely to human trigger. Convective snowfall in the wake of the storm may obscure the evidence of these wind slabs.

A weak layer of widespread surface hoar is buried 40-80 cm deep. It may sit over a crust on solar aspects. Incremental loading from successive storms, strong winds, and mild temperatures have strengthened the slab character and increased the depth of the snow above, creating the potential for larger avalanches with serious consequences. Read more about surface hoar on our forecaster blog!

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • Use conservative route selection and resist venturing out into complex terrain.
  • Even brief periods of direct sun could produce natural avalanches.

Problems

Persistent Slabs

An icon showing Persistent Slabs

A weak layer of surface hoar is buried 40-80 cm deep, and human-triggering is likely. Over the past several days, large avalanches have been observed extensively across the region. The distribution of this problem extends to all aspects and elevations, but north to east aspects near treeline have been a hot-spot for reactivity.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3.5

Wind Slabs

An icon showing Wind Slabs

Incremental snowfall and recent strong winds formed reactive wind slabs in the alpine and open areas at treeline that remain likely to human-trigger. If triggered, wind slabs have the potential to step-down to deeper weak layers. This problem overlaps with where cornices may be reaching their breaking point.

Aspects: North, North East, East, South East, North West.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2.5

Valid until: Mar 6th, 2020 4:00PM