Sea to Sky Avalanche Forecast

Mar 6th, 2020 4:00PM

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

Slabs formed from Thursday's storm may take a bit of time to bond to previous surfaces. Watch for storm slabs in sheltered terrain and wind slabs on lee slopes at higher elevations. Cornices are likely large and looming.

Summary

Confidence

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

Weather Forecast

FRIDAY NIGHT: Mostly clear skies, light south wind, alpine temperature -10 C.

SATURDAY: Mostly cloudy with isolated flurries, accumulation 5 to 10 cm, light southwest wind, alpine temperature -10 C, freezing level 700 m.

SUNDAY: Mostly cloudy, light west wind, alpine temperature -10 C, freezing level 800 m.

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

Avalanche Summary

On Friday, explosives triggered several storm and wind slab avalanches within the recent storm snow. They were generally 20 to 50 cm deep, in alpine terrain, and large (size 2 to 2.5).

On Thursday, small storm slab avalanches were triggered naturally and by riders during the storm. They were reported to be touchiest in lee, northerly aspects.

Natural avalanche activity is expected to taper with a calmer weather pattern. 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 fell with strong to extreme south to southwest wind, forming 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

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • Surface hoar distribution is highly variable. Avoid generalizing your observations.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

Problems

Storm Slabs

An icon showing Storm Slabs

Likelihood

Possible-Likely

Expected Size

1 - 2.5

Around 25 to 35 cm of snow from Thursday is consolidating into a slab in sheltered terrain 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 terrain features. These slabs may remain touchy to riders this weekend. Cornices have also likely grown large and could fail from the weight of a human.

Aspects:

All aspects.

Elevations:

All elevations.

Persistent Slabs

An icon showing Persistent Slabs

Likelihood

Unlikely-Possible

Expected Size

2 - 3

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 still 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.

Valid until: Mar 7th, 2020 5:00PM