Avalanche Forecast

Lizard Range and Flathead

Date issued

Feb 15, 2018 - 5:13 PM

Valid until

Feb 16, 2018 - 2:00 PM

Prepared by

jmcbride

Wind slabs, cornices and deeply buried weak layers are making for tricky conditions. The best approach is to choose conservative terrain, minimize your exposure to overhead hazards and avoid wind-loaded areas.

Regular season
Thursday - February 15, 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.

Friday - February 16, 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.

Saturday - February 17, 2018
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

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.

Below 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.

Avalanche Problem 1: Wind Slabs

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

New snow and wind have formed wind slabs in wind exposed areas at upper elevations in the Fernie area. This new snow overlies a variety of old surfaces including hard wind scour, old wind slab, and crusts.

Travel and Terrain Advice
  • If triggered, storm slabs may step down to deeper layers resulting in large avalanches.
  • Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.

Avalanche Problem 2: Deep Persistent Slabs

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

Large avalanches have been running on deep weak layers. Wind loading, fragile cornices, and smaller avalanches are all possible triggers, as well as thin or rocky snowpack areas where human triggering may also be possible.

Travel and Terrain Advice
  • Avoid steep convexities or areas with a thin or variable snowpack.
  • Be aware of the potential for large, deep avalanches.
  • Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.

Avalanche Problem 3: Cornices

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

Cornices have triggered very large avalanches recently. Be especially wary of long runout distances in avalanche paths, and the possibility of mature timber being taken out by a surprisingly large avalanche.

Travel and Terrain Advice
  • Avoid steep slopes below cornices.
  • Give cornices a wide berth when traveling on or below ridges.

Avalanche Summary

Thursday natural storm slab and loose storm snow avalanches up to size 1.5 were reported to have occurred overnight with active loading during the storm.

Explosive control work and ski cutting on Wednesday produced widespread storm slab results up to size 2, between 1600-2100 m.

On Tuesday skiers were able to cut size 1.5 wind slabs on north east features at treeline. Wind slabs to size 2 were also reported, starting at the base of steep head walls.

On Saturday we received reports of impressive sizes of cornice chunks breaking off a tree line ridge feature near Harvey Pass (Flathead area), running far into the forest and meadow below. See here for photos.

Avalanche activity on deeper layers has tapered off for now, but it's best to avoid likely trigger points such as thick-to-thin snow pack areas and also close to the base of rocky headwalls.

Snowpack Summary

About 30-40 cm of new storm snow and wind have created wind slabs at upper elevations.  This new snow overlies old wind slabs on leeward slopes at treeline and above, and a mix of surface hoar, facets and sun crusts on solar aspects.

Below 1700m, the new snow covers a rain crust from last Wednesday.

For the past month there has been regular avalanche activity on multiple weak layers in the mid and lower 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.

The take home message is that several weak layers are still lurking in the snowpack and they deserve a lot of respect. Conservative terrain use is recommended while avoiding all overhead hazard.

Weather Forecast

TONIGHT: Cloudy with clear periods, light flurries. Accumulation trace. Ridge wind moderate to strong, southwest. Temperature -10. Freezing level valley bottom.

FRIDAY: Cloudy with sunny periods, light flurries. Accumulation trace. Ridge wind moderate, west. Temperature -5. Freezing level valley bottom.

SATURDAY: Snow. Accumulation 20-30 cm. Ridge wind light to moderate, east. Temperature -6 C. Freezing level valley bottom.

SUNDAY: Mainly cloudy, light flurries. Accumulation trace. Ridge wind light to moderate, east. Temperature -17. Freezing level 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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