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Avalanche Forecast

Archived

Feb 12th, 2021–Feb 13th, 2021

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Coast.

Watch for recently formed wind slabs on a wide range of aspects at higher elevations. Southeast to southwest aspects are the prime candidates for holding the most reactive slabs.

Confidence

High -

Weather Forecast

Friday night: Becoming cloudy with light flurries beginning. Moderate east winds.

Saturday: Cloudy with continuing scattered flurries bringing up to 5 total cm of new snow, easing overnight. Light east or northeast winds, easing over the day. Alpine high temperatures around -10.

Sunday: Cloudy with isolated flurries and a trace of new snow, increasing overnight. Light east winds, increasing overnight. Alpine high temperatures around -6.

Monday: Cloudy with easing flurries and up to 10 cm of new snow from the overnight period. Light east winds. Alpine high temperatures around -5.

Avalanche Summary

A MIN report from the Ledge Basin area on Thursday described small new wind slabs triggerable in leeward features at higher elevations, a product of recent northeast outflow winds. Similar conditions were observed on the North Shore on Friday morning.

There have been no other reports of avalanche activity in the region since early last week when a widespread natural avalanche cycle up to size 3 (very large) took place in the North Shore mountains. Dense bridging layers of snow and crust are expected to have effectively neutralized the problem since that time, although some uncertainty exists with regard to higher alpine locations.

Snowpack Summary

Elevated northerly winds on Thursday redistributed limited loose snow into small but reactive new wind slabs in the immediate lee of exposed terrain features at higher elevations.

The snow surface otherwise consists of a thin cover of low density snow (where not windblown) over a mix of thin breakable crust, old wind-affected snow, and older wind slabs that have been losing cohesion under the influence of prolonged cold temperatures. 30-40 cm of gradually faceting storm snow below this surface, a more supportive crust solidly caps the snowpack below about 1400 metres. This crust may be absent at higher elevations.

100-150 cm of snow sits over a widespread persistent weak layer. This weak layer consists of a thick crust with weak facets on top of it in many areas. In most areas where it remains preserved, this layer is likely not triggerable due to bridging by overlying dense snow and crusts (this applies to the North Shore). There is some concern for the possibility of continued reactivity in steep terrain at higher elevations in the interior and north of the region where it has not previously avalanched and where the overlying snowpack may have failed to form an effective bridge over it.

Click here to check out North Shore Rescue's snowpack update from February 12. It's an excellent snapshot of current conditions on the North Shore.

Terrain and Travel

  • Small avalanches can have serious consequences in extreme terrain. Carefully evaluate your line for wind slab hazard before you commit to it.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.