Avalanche Forecast

Northwest Coastal

Date issued

Dec 31, 2017 - 4:11 PM

Valid until

Jan 1, 2018 - 2:00 PM

Prepared by

mgrist

Pockets of reactive wind slab remain a concern for wind-exposed alpine and treeline areas. New snow and south west wind on Monday will heighten avalanche danger.

Regular season
Sunday - December 31, 2017
Alpine

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Below Treeline

1 - Low

Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

Natural and human-triggered avalanches unlikely.

Small avalanches in isolated areas or extreme terrain.

Monday - January 1, 2018
Alpine

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Below Treeline

1 - Low

Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

Natural and human-triggered avalanches unlikely.

Small avalanches in isolated areas or extreme terrain.

Tuesday - January 2, 2018
Alpine

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Treeline

1 - Low

Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

Natural and human-triggered avalanches unlikely.

Small avalanches in isolated areas or extreme terrain.

Below Treeline

1 - Low

Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

Natural and human-triggered avalanches unlikely.

Small avalanches in isolated areas or extreme terrain.

Avalanche Problem 1: Wind Slabs

What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?

Wind slabs may be lingering around ridge crests, exposed gullies and cross-loaded slopes. These wind slabs may be poorly bonded to the buried mid-December crust layer and reactive to human triggers such as a skier or rider.

Travel and Terrain Advice
  • Be cautious as you transition into wind affected terrain.
  • Watch for whumpfing, stiff or hollow sounding snow, and shooting cracks.

Avalanche Summary

On Thursday an isolated wind slab release (size 1.5) was observed on an actively wind loaded, steep terrain feature in the northern part of the region.

Snowpack Summary

Cold temperatures and strong winds (from the south east, and more recently from the west) have affected the surface snow over the past week, scouring some slopes down to an old crust and forming hard deposits in many other areas. There are some lingering wind slabs, found on a variety of old surfaces including a thick melt-freeze crust that formed in mid-December.

In non-wind affected terrain, 20-40 cm of unconsolidated (aka faceted or 'sugary') snow overlies the mid-December crust layer. This snow has been sluffing in steep terrain.

Beneath the mid-December crust the snowpack is reported to be generally strong with the possible exception of areas around Stewart and northern parts of the region where the late-October, basal crust can be found near the base of the snowpack. Weak sugary snow may exist around this basal crust and could be triggered from shallow snowpack areas.

Weather Forecast

We're looking at a small amount of snow through Monday and some lingering flurries for the week as temperatures gradually warm up.

MONDAY: Cloudy, flurries. Accumulation 5-10 cm. Ridge wind moderate to strong southwest. Temperature -6. Freezing level 400 m with an above freezing layer (AFL) from 1200m to 1700m.

TUESDAY: Cloudy with some flurries (2-5 cm possible). Ridge wind moderate south west. Temperature -5. Freezing level 500m with an AFL from 1200m to 1700m.

WEDNESDAY: Cloudy with isolated flurries. Ridge wind moderate from the south. Temperatures -4. Freezing level 400m with an AFL from 1100m to 1900m.

Danger Ratings Explained

1 - Low

Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

Natural and human-triggered avalanches unlikely.

Small avalanches in isolated areas or extreme terrain.

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

Natural avalanches possible; human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

4 - High

Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

Natural avalanches likely; human-triggered avalanches very likely.

Large avalanches in many areas; or very large avalanches in specific areas.

5 - Extreme

Avoid all avalanche terrain.

Natural and human-triggered avalanches certain.

Large to very large avalanches in many areas.

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