Avalanche Forecast

Lizard Range and Flathead

Date issued

Dec 10, 2017 - 3:49 PM

Valid until

Dec 11, 2017 - 2:00 PM

Prepared by

jlammers

Warm temperatures and solar radiation may elevate the avalanche danger at higher elevations on Monday.

Regular season
Sunday - December 10, 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.

Monday - December 11, 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 12, 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.

Avalanche Problem 1: Wind Slabs

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

Variable winds from last week have formed wind slabs 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?

The band of warm air associated with the inversion has been hovering at elevations higher than most peaks in the area. If this band of warm air drops, we may see a round of loose wet avalanche activity in steep, sun-exposed terrain.

Travel and Terrain Advice
  • Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.
  • Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.

Avalanche Summary

On Friday a few stiff wind slabs to size 1.5 were explosive-triggered at treeline. No other avalanches have been reported since. 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.

The band of warm air associated with the inversion has been hovering at elevations higher than most peaks in the area. If this band of warm air drops, we may likely see a round of loose wet avalanche activity in steep, sun-exposed terrain.

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

Snowpack Summary

Stiff wind slabs exist on a wide range of aspects on alpine and exposed treeline slopes. In sheltered treeline and below treeline terrain, I suspect light amounts of low-density snow intermingle with surface hoar and surface facets.

Roughly 30-60 cm below the surface you'll likely find a hard crust that was buried on November 26. This crust is approximately 30 cm thick and extends from 1600 m to mountain top on all aspects. Below this crust, the snowpack is moist to ground. Average snowpack depths at treeline elevations in the region range from 80-120 cm.

Weather Forecast

Expect mainly clear skies and valley cloud for the forecast period. An inversion is forecast for all 3 days with high alpine temperatures peaking at 5 degrees on Monday and Tuesday. Winds are expected to remain light to moderate from the west.

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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