Date issued

Dec 20, 2017 - 8:00 AM

Valid until

Dec 21, 2017 - 8:00 AM

Prepared by

percy woods

A touchy surface hoar layer below the recent storm snow has heightened the chance of skier triggered slides. It is a good time for conservative terrain choices.

Regular season
Wednesday - December 20, 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

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.

Thursday - December 21, 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

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.

Friday - December 22, 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

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

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.

Avalanche Problem 1: Storm Slabs

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

Recent storm snow continues to settle into a slab.  Expect the slab to be increasingly sensitivity as you transition into wind effected terrain. Steeper solar slopes harbor a thin crust layer below the storm snow and a facet surface hoar combo BTL.

Travel and Terrain Advice
  • Watch for whumpfing, hollow sounds, and shooting cracks.
  • Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Avalanche Problem 2: Wind Slabs

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

Moderate gusting to strong N-NE winds have been forming reverse loaded windslab in wind exposed areas at and above treeline.  These slabs may have surface hoar or crust underneath leading them to be sensitive to human triggering.

Travel and Terrain Advice
  • Be cautious as you transition into wind affected terrain.
  • Make observations and assess conditions continually as you travel.

Avalanche Summary

A natural avalanche cycle has been continuing over the last 48hrs with over 40 avalanches up to size 3 recorded in the highway corridor. Most slides have been in the size 1.5 to 2 range failing on the Dec 15th surface hoar layer. Avalanches have been on all aspects and elevations including numerous below treeline events.

Snowpack Summary

40cm of storm snow sits on top of the Dec 15 surface hoar/persistent weak layer. On steeper solar aspects this layer is a crust and/or a crust with small surface hoar on top. The crust runs well up into the alpine on steep south aspects. Deeper in the pack there are a series of crust layers that are currently well bonded to neighboring layers.

Weather Forecast

Sunny with cloudy periods, a trace of snow and alpine temperatures in the -12C range. Thursday should give us light flurries, moderate westerly wind and alpine temperatures of -10C.

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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