Avalanche Forecast

Lizard Range and Flathead

Date issued

Dec 8, 2017 - 4:27 PM

Valid until

Dec 9, 2017 - 2:00 PM

Prepared by

cgarritty

Avalanche danger is tightly linked to solar exposure and warming. Look to shaded aspects to find the best snow and safest riding.

Regular season
Friday - December 8, 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

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.

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.

Saturday - December 9, 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

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.

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.

Sunday - December 10, 2017
Alpine

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.

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.

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?

A recent wind shift from southwest to north means that wind slabs now exist on a wide range of aspects at higher elevations. Be especially cautious of reverse loaded or cross-loaded slopes that see sun exposure.

Travel and Terrain Advice
  • Be careful with wind loaded areas, especially near ridge crests and roll-overs.
  • Use ridges or ribs to avoid pockets of wind loaded snow.

Avalanche Problem 2: Loose Wet

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

Warm, sun-exposed slopes could continue to produce wet loose avalanches either naturally or with rider triggers on Saturday - especially in steeper terrain. This problem may expand to northerly aspects as warming persists.

Travel and Terrain Advice
  • Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.
  • Be cautious of sluffing in steep terrain, particularly where the debris flows into terrain traps.

Avalanche Summary

Reports from Tuesday included several observations of wind slabs releasing to Size 2 in the Fernie area. These were mainly triggered with explosives but one Size 1.5 slab did release with skier traffic. Looking forward, we should see a gradually diminishing potential for wind slab releases as warm daytime temperatures and overnight cooling promote bonding in the upper snowpack.

Please submit your observations to the Mountain Information Network (MIN).

Snowpack Summary

Solar and temperature crusts are expected to have formed on the surface at higher elevations over the past two days. Below the surface, recent shifting winds redistributed loose snow at higher elevations, crossloading and forming wind slabs on a wide range of aspects at treeline and above. Below this wind effect, roughly 30-60 cm of storm snow is expected to be bonding well to the underlying crust that was buried on November 26. This crust is approximately 30 cm thick and extends from 1600 m to mountain top elevations on all aspects. Below this capping crust, the snowpack is moist to ground. Average snowpack depths at treeline elevations in the region range from 80-120 cm.

Weather Forecast

Saturday: Mainly sunny with valley cloud due to lingering temperature inversion. Light southwest winds. Freezing level to 3500 metres with alpine temperatures around +3. Cooler at lower elevations.

Sunday: Mainly cloudy. Light west winds. Freezing level to 3500 metres with alpine temperatures around +5. Cooler at lower elevations.

Monday: Mainly sunny with lingering valley cloud. Light southwest winds. Freezing level to 3500 metres with alpine temperatures around +6. Cooler at lower elevations.

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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