Date issued

Nov 25, 2017 - 4:00 PM

Valid until

Nov 26, 2017 - 4:00 PM

Prepared by

garth lemke

Developing windslab at Treeline and above on Saturday.  25+ cm possible with incoming storm on Sunday afternoon will increase hazard to High on Monday. 

Regular season
Sunday - November 26, 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.

Monday - November 27, 2017
Alpine

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.

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.

Tuesday - November 28, 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.

Avalanche Problem 1: Persistent Slabs

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

This is a complex problem which is hard to assess and predict. Give yourself a wide margin and make conservative terrain choices.

Travel and Terrain Advice
  • Be wary of slopes that did not previously avalanche.
  • Be aware of the potential for wide propagations.

Avalanche Problem 2: Wind Slabs

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

Be wary of areas where new snow transport has created pockets of windslab. Watch for sudden changes in texture and hardness. Typically occurring on lee aspects but may be influenced by local terrain.

Travel and Terrain Advice
  • Use caution in alpine lee areas. Recent snow is available for transport given the current winds.

Avalanche Summary

No field patrol on Friday. Thursday had numerous persistent size 2.5 slab avalanches. They failed at treeline and in the lower alpine as a result of warm temperatures, rain and additional snow loading. On Nov. 22nd a field team remote triggered 3 simultaneous size 2 persistent slabs 60-150m away on either side of the wind scoop at parkers ridge.

Snowpack Summary

Cooler temperatures have formed a surface crust from the previous moist snow below 2300m. A persistent slab between 40cm - 200cm thick sits over the Halloween Crust low in the pack. This crust can be found up to 2,700m depending on its location and is between 20cm - 40cm above the ground. Wind slabs likely exist in the upper alpine.

Weather Forecast

Flurries Saturday with mod SW winds .  Alpine Temperatures up to -5.  Sunday - snow with increasing accumulation through the afternoon with 25 cm possible by early Monday morning, freezing level rising to 2200m then falling to valley bottom as storm passes.  Moderate SW winds will accompany this storm.

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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