Avalanche Forecast

Issued: Mar 7th, 2020 4:00PM

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

Avalanche Canada mconlan, Avalanche Canada

Slabs formed from Thursday's storm may take a bit more time to bond to previous surfaces. Watch for storm slabs in sheltered terrain, wind slabs on lee slopes, and avoid looming cornices. Watch for deteriorating snow on sun-exposed slopes when the sun is shining.

Summary

Confidence

High - Confidence is due to a stable weather pattern with little change expected.

Weather Forecast

SATURDAY NIGHT: Mostly cloudy with isolated flurries, accumulation 5 to 10 cm, light northwest wind, alpine temperature -11 C.

SUNDAY: Mix of sun and cloud, light northwest wind, alpine temperature -11 C.

MONDAY: Clear skies, light west wind, alpine temperature -10 C, freezing level 900 m.

TUESDAY: Cloudy with snowfall, accumulation 5 to 10 cm, moderate southwest wind, alpine temperature -6 C, freezing level 900 m.

Avalanche Summary

On Friday, the storm snow was reactive to riders and explosives. Many small to large (size 1 to 2.5) avalanches were triggered, generally 20 to 50 cm deep. There was also a report of a large conrice failure near Whistler, showcased in this MIN.

Natural avalanche activity is expected to taper with a calmer weather pattern, with the exception of periods of strong sun, where the storm snow on sun-exposed slopes could moisten and deteriorate. Human triggering of the storm and wind slabs may remain possible this weekend until the snow bonds to previous surfaces.

Snowpack Summary

Thursday's storm dropped around 25 to 35 cm of snow across the region. The snow is consolidating into a slab that was reported to be touchy (e.g. in this MIN). The snow is likely gaining strength and starting to bond to underlying layers. The snow fell with strong to extreme south to southwest wind, which formed wind slabs in lee terrain features at treeline and alpine elevations.

A weak layer of surface hoar crystals and/or faceted grains may be found around 100 cm deep on northerly aspects at treeline and lower alpine elevations. For some of the region, the layer may have been destroyed by strong wind immediately before burial on February 22nd, but it may still exist in sheltered terrain features in parts of the region. Where it is found, it has been reactive in snowpack tests. This persistent weak layer warrants investigation and a conservative terrain use strategy. Check out the latest forecaster blog that offers a deeper dive into these conditions.

Weak faceted snow and melt-freeze crusts exist near the base of the snowpack in some of the region, particularly the eastern and northern parts. This layer is considered dormant, as it hasn't produced an avalanche since February 20th. This layer may require a very large load, such as a cornice fall, or rapid weather changes to reactivate it.

Terrain and Travel

  • The new snow may require another day to settle and stabilize.
  • Carefully evaluate steep lines for wind slabs.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.
  • Surface hoar distribution is highly variable. Avoid generalizing your observations.

Problems

Storm Slabs

An icon showing Storm Slabs

Around 25 to 35 cm of snow from Thursday has consolidated into a slab and may take a couple days to bond to previous surfaces. In exposed terrain at higher elevations, the snow fell with strong to extreme southeast to southwest wind, forming thick wind slabs in lee (northerly) terrain features. These slabs may remain touchy to riders this weekend. Use caution on steep sun-exposed slopes during periods of intense sun, as the storm snow may rapidly deteriorate. Also note that cornices are large and could fail from the weight of a human.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 2.5

Persistent Slabs

An icon showing Persistent Slabs

A weak layer of feathery surface hoar may be found around 100 cm deep on northerly aspects around treeline and lower alpine elevations. This layer may be spotty and only found in sheltered terrain features in parts of the region. Although we haven't heard of any reports of avalanche activity on this layer for over a week, the layer has produced results in snowpack tests, where it exists. Assess the layer in the snowpack prior to committing to avalanche terrain or adopt a conservative mindset to avoid the problem.

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

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Mar 8th, 2020 5:00PM