Avalanche Forecast

Lizard Range and Flathead

Date issued

Feb 18, 2018 - 4:02 PM

Valid until

Feb 19, 2018 - 2:00 PM

Prepared by

mconlan

Recent snow and strong winds have produced touchy wind slabs. Watch for signs of avalanche activity and locally unstable snow, such as whumpfing and shooting cracks.

Regular season
Sunday - February 18, 2018
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

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 - February 19, 2018
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

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 - February 20, 2018
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.

Avalanche Problem 1: Wind Slabs

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

Recent storm snow fell with strong winds that have produced touchy wind slabs in lee features on all aspects. These slabs will likely be reactive to natural and human triggers. Be cautious of overhead exposure on solar aspects when the sun is out.

Travel and Terrain Advice
  • If triggered, the wind slabs may step down to deeper layers, resulting in large avalanches.
  • Choose shallow-angled and sheltered terrain where new snow hasn't been wind-affected.

Avalanche Problem 2: Cornices

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

Cornices have grown in size with the recent storms and have been reactive to explosives. If released, they could produce large avalanches that run far.

Travel and Terrain Advice
  • Avoid travelling below large corniced ridges.
  • Remain well back from corniced ridges, giving them a wide berth.

Avalanche Problem 3: Deep Persistent Slabs

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

Several weak layers are lurking in our snowpack. If triggered, they could propagate far, producing avalanches with high consequences. Watch out for thin spots in the snowpack, where it is more likely to trigger them.

Travel and Terrain Advice
  • Be aware of the potential for wide propagation.
  • Avalanches could run full-path: avoid runout zones of avalanche paths.

Avalanche Summary

Naturally triggered storm slabs were noted up to size 2.5 between 1800 and 2100 m on Sunday.  They were 20 to 40 cm deep and on northerly to easterly aspects.  One of the avalanches was likely triggered by a cornice fall during Saturday's storm.

On Saturday, Many small to large (size 1 to 2) storm slabs and cornices were triggered by explosive control at treeline and alpine elevations. The storm slabs were about 20 cm deep on north to northeast aspects.

Snowpack Summary

Around 50-80 cm of recent snow has created storm slabs. The snow fell with strong variable winds, creating wind slabs in direct lee features on all aspects. This overlies a surface hoar layer and a melt-freeze crust buried mid-February up to 1800 m, and old wind slabs and a sun crust at higher elevations.

Deeper in the snowpack, a widespread weak layer from mid-December composed of facets, crusts, and surface hoar is 120-160 cm deep. Also, a rain crust with sugary facets buried in late November is near the base of the snowpack. There has been regular avalanche activity on these layers over the past month. If triggered, they could produce large, destructive avalanches with high consequences.

Weather Forecast

MONDAY: Partly cloudy, light northeasterly winds, alpine temperature -15 C, freezing level below valley bottom.

TUESDAY: Mostly sunny, light westerly winds, alpine temperature near -12 C, freezing level below valley bottom.

WEDNESDAY: Mostly sunny, moderate westerly winds, alpine temperature near -11 C, freezing level below valley bottom.

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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