Sea to Sky Avalanche Forecast

Issued: Feb 14th, 2021 4:00PM

Mon Feb 15th Current Conditions
Alpine Considerable Treeline Moderate Below Treeline Moderate
Tue Feb 16th 2 Day Outlook
Alpine Considerable Treeline Moderate Below Treeline Moderate
Wed Feb 17th 3 Day Outlook
Alpine Considerable Treeline Moderate Below Treeline Low

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

Take a mindset of initial assessment with you as you investigate overnight snowfall. It's more than just the new snow that has danger elevated. It is adding to (and obscuring) reactive, slow-healing wind slabs already scattered across the region.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Sunday night: Cloudy with increasing flurries bringing about 5 cm of new snow. Light to moderate south or southwest winds.

Monday: Cloudy with continuing flurries from the overnight period leaving us with about another 5 cm of new snow with 2-day snow totals of 5-15 cm, easing over the day. Light south winds shifting northwest by afternoon. Alpine high temperatures around -8.

Tuesday: Cloudy with scattered flurries continuing from the overnight period bringing up to about 5 cm of new snow. Light to moderate southwest winds becoming northwest in the alpine. Alpine high temperatures around -7.

Wednesday: A mix of sun and cloud. Light variable, mainly north winds. Alpine high temperatures around -8.

Avalanche Summary

Another fatal avalanche involvement occurred in the region on Saturday in the Brandywine valley. The person caught was carried several hundred metres over steep, rugged terrain and through treed slopes below. The avalanche is described as a size 1 (small) wind slab on a southwest aspect at 1700 metres. The incident report can be seen here.

On Friday, a large (size 2.5), fatal avalanche was triggered by skiers at 2200 metres on a west-facing slope on Phalanx Mountain. The avalanche is described as a wind slab that formed to the lee of recent strong east winds. Two people out of a group of three were involved in the avalanche and one person was killed. The incident report can be seen here. A second, smaller (size 1.5) wind slab was triggered by skiers on a nearby slope, again causing injury to the person involved.

A bout of strong northerly winds on Thursday caused conditions in the region to change rapidly, with new and touchy wind slabs forming in unusual places. Numerous natural releases from size 1 to size 2 were observed in the Whistler area above about 1900 metres on and since Thursday. 

It is important to note wind has not affected elevation bands uniformly across the region, with heavy wind effect and slab formation noted even below treeline in some areas. This is a critical piece of information as new snow obscures existing wind slab formations.

Two more skiers were involved in an avalanche in the Supercouloir feature of Mamquam Mountain on Thursday. This avalanche was a natural wind slab release ands again resulted in serious injuries and an urgent evacuation by helicopter.

Snowpack Summary

About 15 cm of new snow (over a two day period) is expected to accumulate in the region by the end of the day on Monday. This will feed into existing wind slab problems brought on by powerful east and northeast winds that have been redistributing loose snow into reactive wind slabs. Winds have been circling the compass as we wait for a forecast shift to the southwest, expanding problems to all aspects.

Forecast snow will otherwise add to around 15 cm of older low density snow in shaded, sheltered areas and to more widespread wind-affected snow. This previous surface snow has been transforming into weak, faceted grains under recent cold temperatures. On solar aspects, a thin recent sun crust may be found near the new snow interface or beneath recently wind transported snow. Both of these interface types are contributing to the reactivity of new wind slabs.

Below the evolving surface, 50-100 cm of settled storm snow sits on a persistent weak layer from late January that consists of facets at upper elevations, surface hoar in sheltered areas, a melt-freeze crust below 1900 m, and a sun crust on south-facing slopes. There could be more than 100 cm on this layer in wind loaded areas. Although this structure is suspect, we have no recent reports of avalanches failing at this interface within the region.

A crust from early December, currently considered dormant, may be found around 200+ cm deep in the snowpack.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be aware of highly variable recent wind loading patterns.
  • Keep your guard up at lower elevations. Wind slab formation has been extensive.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

Problems

Wind Slabs

An icon showing Wind Slabs

Likelihood

Very Likely

Expected Size

1 - 2.5

New snow and shifting winds will feed into existing wind slab problems formed in response to recent outflow winds. Especially new but also recent slabs will be sensitive to human triggering on Monday. This is an all aspects, increasing avalanche problem. Some local winds have reached into lower elevations. Keep your guard up below treeline.

Recent faceting and loss of cohesion in cornices can make them brittle and prone to fail. Give them a wide berth from above and below.

Aspects:

All aspects.

Elevations:

All elevations.

Valid until: Feb 15th, 2021 4:00PM

Forecast Trend

The latest forecast danger ratings, broken down to elevation. See how an elevation is trending.