Sea to Sky Avalanche Forecast

Mar 4th, 2020 4:00PM

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

An intense storm will hammer the region with snow and wind on Thursday. Slabs will rapidly build over the day. Treat the danger as HIGH if you find 30+ cm of new snow or during periods of rapid loading from snowfall and/or wind.

Summary

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

WEDNESDAY NIGHT: Cloudy with snowfall, accumulation 5 to 10 cm, moderate to strong southwest wind, alpine temperature -9 C, freezing level 600 m.

THURSDAY: Cloud with snowfall, accumulation 15 to 25 cm, strong to extreme southwest wind, alpine temperature -6 C, freezing level 1000 m.

FRIDAY: Morning snowfall then mix of sun and cloud with isolated flurries, accumulation 5 to 10 cm, light southwest wind, alpine temperature -10 C, freezing level 800 m.

SATURDAY: Morning snowfall then a mix of sun and cloud, accumulation 5 to 10 cm, light southwest wind, alpine temperature -10 C, freezing level 700 m.

Avalanche Summary

A small storm slab was triggered naturally in the region on Monday on a northerly aspect out of steep terrain. Otherwise, no new avalanches were observed.

Avalanche activity is expected to spike on Thursday during the stormy weather.

Snowpack Summary

The next storm on Wednesday night into Thursday will drop around 20 to 30 cm of snow across the region. The snow will likely consolidate into a storm slab as the day unfolds, with particularly touchy conditions during periods of rapid snow loading. The wind will be strong from the southwest 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

  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Dial back your terrain choices if you are seeing more than 20 cm of new snow.
  • 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 - 2.5

Around 20 to 30 cm of snow is forecast to accumulate across the region on Thursday. Storm slabs will grow over the day and become touchy during periods of rapid loading from snowfall and/or strong wind. The snow will fall with strong southwest wind, so the deepest deposits will be in lee terrain features. Use added caution if you find more than 20 cm of snow accumulate from the storm.

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 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 5th, 2020 5:00PM