Avalanche Forecast

Sea To Sky

Date issued

Dec 18, 2017 - 4:30 PM

Valid until

Dec 19, 2017 - 2:00 PM

Prepared by

mgrist

Fresh storm slabs will be driving the avalanche danger on Tuesday. Be extra vigilant on down wind (lee) features below ridge crests.

Regular season
Tuesday - December 19, 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.

Wednesday - December 20, 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.

Thursday - December 21, 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

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: Storm Slabs

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

Winds during Tuesday's storm will be from the (north) east - which is not the usual pattern we see. Watch out for storm slabs on west through northerly aspects.

Travel and Terrain Advice
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Avoid steep convex slopes.

Avalanche Summary

On Monday, ski cutting and explosives control work produced several Size 1 to 1.5 storm slabs on steep northerly features at higher elevations.

On Sunday, natural and cornice triggered storm slabs to Size 1 were reported on northerly aspects in the alpine.

Snowpack Summary

10-30 cm of new snow covers the melt-freeze crust that formed on all aspects and elevations in early December. On high north aspects this crust is thin with dry, sugary snow crystals (facets) below.

Moderate winds from the south (west) have redistributed snow, creating isolated soft slabs on downwind slopes and behind ridges (north through east aspects).

Beneath the surface, the upper snowpack is well settled and overlies a thin layer of facets on the late-November rain crust, which is now down approximately 60 cm at tree line elevations.

The lower snowpack is well settled and consists of several crusts that formed in the early season.

Weather Forecast

Active weather returns on Tuesday with moderate amounts of snow and cool temperatures.

TUESDAY: Snow. 5cm overnight with 10-15cm accumulation throughout the day. Ridge wind moderate from the east. Temperature near -5. Freezing level 500 m.

WEDNESDAY: Sunny with cloudy periods. Ridge wind moderate northerly. Freezing level at the surface.

THURSDAY: Cloudy with isolated flurries. Ridge wind moderate from the north west. Temperature near -3. Freezing level 400 m.

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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