Avalanche Forecast

Sea To Sky

Date issued

Dec 17, 2017 - 4:51 PM

Valid until

Dec 18, 2017 - 2:00 PM

Prepared by

mgrist

Wind-blown snow is driving the avalanche danger on Monday. Watch for how the new snow is bonding to the old surface.

Regular season
Sunday - December 17, 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 - December 18, 2017
Alpine

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.

Treeline

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.

Below 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.

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.

Avalanche Problem 1: Wind Slabs

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

The new storm snow may be easily triggered, especially in areas with additional loading from wind.

Travel and Terrain Advice
  • Watch for signs of instability such as whumpfing, shooting cracks or recent natural avalanches.
  • Be cautious as you transition into wind affected terrain.
  • Be careful with wind loaded pockets in down wind areas, especially near ridge crests and roll-overs.

Avalanche Summary

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

Avalanche activity is expected to increase with the wind-driven snow on Monday, especially on north through east aspects at higher elevations.

Snowpack Summary

10-20 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

Monday will see a brief lull in the active weather pattern before significant precipitation arrives on Tuesday.

MONDAY: Cloudy with isolated flurries. Accumulation of 5 cm possible. Ridge wind light from the west. Temperature near -2. Freezing level 800 m.

TUESDAY: Snow. Accumulation 15-25 cm. Ridge wind moderate from the southeast. Temperature near -4. Freezing level 500 m.

WEDNESDAY: Sunny with cloudy periods. Ridge wind moderate northerly. Freezing level 600 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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