Date issued

Nov 18, 2017 - 4:00 PM

Valid until

Nov 19, 2017 - 4:00 PM

Prepared by

tim haggarty

Forecast snowfall amounts are uncertain but moderate to strong winds will be sustained; expect avalanche hazard to increase. Both natural and human triggered slabs have been reported near treeline.

Regular season
Sunday - November 19, 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

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 - November 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

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 - November 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

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?

Strong West winds were again moving a great deal of snow today and treeline areas are also starting to be affected. These winds will continue through Sunday and, with more snow in the forecast, expect these slabs become even more developed.

Travel and Terrain Advice
  • Use caution in lee areas. Recent wind loading has created wind slabs.
  • Choose ice climbs that are not exposed to avalanches from above.

Avalanche Problem 2: Storm Slabs

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

The snow that fell on Halloween became faceted by the early November cold snap. Soft slabs of snow now sit above this weak snow and have been reactive to skier traffic and small triggers such as sluffs out of rocky terrain.

Travel and Terrain Advice
  • Minimize exposure to steep, planar slopes.

Avalanche Summary

Continued reports of storm and wind slab activity are coming in; most notably a sz 2 slab at treeline just west of the Bourgeau Left ice climb reported by the Sunshine patrol. This slab was undoubtedly triggered by sustained wind loading late in the day Friday and is likely to have failed on facets over the Halloween crust.

Snowpack Summary

Light flurries again today with moderate West winds. 15 to 25cm of storm snow in the last 72 hours. The alpine snowpack ranges from 50-100 cm across the region with the main feature to watch in the snowpack being a layer of facets now buried 25 to 40 cm . Below 2700m these facets sit above a temperature crust that was buried on Halloween.

Weather Forecast

A Southwesterly flow arrives midday Sunday favoring Northern areas. Models disagree on snow quantities but 10 to 25cm should be the range. Generally temps will remain in the -5 to -10C range but a brief spike in freezing level would not be a surprise with the arrival of this moist pacific air. Moderate to strong winds will continue through Sunday.

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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