Date issued

Dec 3, 2017 - 4:00 PM

Valid until

Dec 4, 2017 - 4:00 PM

Prepared by

ian jackson

Good ski conditions exist in the alpine, but the winds are forecast to pick up on Monday. Watch for fresh windslab formation and isolated avalanches out of extreme terrain running on the Halloween facet layer

Regular season
Monday - December 4, 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.

Tuesday - December 5, 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.

Wednesday - December 6, 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: Persistent Slabs

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

Natural avalanche activity has tapered, but concern remains for human triggering of the weak snow on this layer. Previously, slab avalanches have been triggered above ~ 2400m where the Nov. 23rd crust fades out. Shallow alpine areas warrant caution.

Travel and Terrain Advice
  • Avoid shallow snowpack areas where triggering is more likely.
  • 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?

Up to 50cm of recent snow is available for transport TL and above. So far only light, gusting moderate, SW winds have created soft slabs and wind effect but watch for this to change as the winds increase from the NW on Monday.

Travel and Terrain Advice
  • Watch for surface cracking and stiffer surface layers of snow. Avoid wind loaded terrain.
  • Use caution in lee areas. Recent wind loading has created wind slabs.

Avalanche Summary

A few size 2's and one size 3 were observed today with good visibility on a flight from Lake Louise to the Wapta . All were in the high alpine (above 2800m) on E/NE aspects in steep, extreme terrain. Most appeared to step down to near ground, likely the Halloween facets. Triggers were wind loading and cornice failures.

Snowpack Summary

Above 2500m, 60cm of snow from last week is being blown into soft windslabs in exposed locations. Below 2500m, up to 30 -50 cm of snow lies over the Nov 27th and Nov 23rd crusts. Both of these now overly the Halloween crust/ facet layer that sits 30-50cm above the ground. This lower layer presents as a facet layer above 2500m and as a crust below.

Weather Forecast

A ridge is forming over the forecast region. The more stable pattern that we are entering into will see temperatures drop to -10 to -15 values at treeline for the 3 day period at least. Watch for wind speeds to increase in to the moderate range for Monday.

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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