Date issued

Nov 26, 2017 - 4:47 PM

Valid until

Nov 27, 2017 - 4:00 PM

Prepared by

snow safety

Avalanches are continuing to run on the Halloween persistent weak layer. Conservative route choices are in order.

Regular season
Sunday - November 26, 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

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

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 - 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

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: Persistent Slabs

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

New snow and rain below 1900 m have added extra weight to the snowpack. The Halloween persistent weak layer remains active as indicated by fresh avalanche activity reported at Lake Louise (see avalanche details).

Travel and Terrain Advice
  • 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?

Fresh snow and mod to strong SW winds will have created fresh wind-slabs in the alpine.

Travel and Terrain Advice
  • Use caution in lee areas. Recent wind loading has created wind slabs.

Avalanche Summary

Warm temperatures and rain below 1900 m have weakened the snow-pack. Lake Louise Ski Hill triggered a bunch of avalanches up to size 2.5 with explosives on Sunday and there was a boarder triggered size 2.5 avalanche in Westbowl. Avalanches were running on the Halloween layer near the base of the snow-pack.

Snowpack Summary

Recent fresh snow and strong south and south west winds will have created fresh wind-slabs in the high alpine. At tree-line and below a warm and rain soaked upper pack sits over the Halloween crust which is 20-40 cm above the ground. The main weakness in the snowpack remains the weak facets associated with the Halloween crust.

Weather Forecast

There will be a cooling trend with freezing levels lowering to around 1200 m on Monday. Light snow expected throughout the day on Monday with accumulations at treeline up to 10 cm. Continued unsettled weather on Tuesday.

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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