Sea to Sky Avalanche Forecast

Mar 3rd, 2020 4:00PM

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

Snowfall and strong wind Tuesday night, followed by sun and cloud on Wednesday. New slabs may remain touchy on Wednesday. Treat the hazard as HIGH if you find 30+ cm of snow accumulation.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

TUESDAY NIGHT: Cloudy with snowfall, accumulation 15 to 30 cm, strong west wind, alpine temperature -10 C, freezing level 1000 m dropping to 500 m.

WEDNESDAY: Mix of sun and cloud, light west wind, alpine temperature -10 C, freezing level 900 m.

THURSDAY: Cloud with snowfall, accumulation 20 to 30 cm, strong southwest wind, alpine temperature -7 C, freezing level 1000 m.

FRIDAY: Morning snowfall then mix of sun and cloud with isolated flurries, accumulation 5 to 10 cm, light south wind, alpine temperature -10 C, freezing level 700 m.

Avalanche Summary

Small wind slabs were reactive to human traffic on Monday. Otherwise, no avalanches were observed.

The last reported avalanche on the surface hoar layer described in the Snowpack Summary was on February 26. However, snowpack tests suggest that this layer remains a concern where it exists in the region.

Snowpack Summary

The next storm on Tuesday night will drop anywhere from 15 to 30 cm of snow across the region, followed by some sunny skies on Wednesday. The snow may consolidate into a storm slab and it may moisten on sun-exposed slopes but stay dry on shaded slopes. The wind will be strong from the west during the storm, so expect wind slab development in lee terrain features, particularly near ridges.

A weak layer of surface hoar crystals and/or faceted grains may be found around 50 to 80 cm deep on northerly aspects at treeline and lower alpine elevations. The layer may have been destroyed by strong wind immediately before burial on February 22nd, but it may still exist in sheltered terrain features. 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.

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.
  • Avoid exposure to steep, sun exposed slopes, especially when the solar radiation is strong.
  • 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.

Problems

Storm Slabs

An icon showing Storm Slabs

Likelihood

Likely

Expected Size

1 - 2

Variable snowfall amounts will accumulate across the region on Tuesday night, with amounts from 15 to 30 cm expected. Both storm and wind slabs will rapidly develop during periods of intense snowfall and strong west wind. Use added caution if you find more than 25 cm of snow accumulate from the storm. Sunny periods on Wednesday could rapidly destabilize the snow on sun-exposed slopes.

Aspects:

All aspects.

Elevations:

All elevations.

Persistent Slabs

An icon showing Persistent Slabs

Likelihood

Unlikely-Possible

Expected Size

1.5 - 2.5

A weak layer of feathery surface hoar may be found around 50 to 80 cm deep on northerly aspects around treeline and lower alpine elevations. This layer may be spotty and only found in sheltered terrain features. 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 4th, 2020 5:00PM