Date issued

Feb 7, 2018 - 4:00 PM

Valid until

Feb 8, 2018 - 4:00 PM

Prepared by

jasper snow safety

25-35cm of storm snow expected overnight Wednesday will increase the Avalanche Danger and may require traffic interruptions Thursday for control work on Highway 93N. Maligne Lake Road will be closed Wednesday evening until Friday evening.

Regular season
Thursday - February 8, 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.

Friday - February 9, 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

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.

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 10, 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

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.

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.

Avalanche Problem 1: Persistent Slabs

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

Field teams observed whumpfing and moderate test results Sunday and Monday in sheltered zones around treeline on these layers. Shallow areas are the most likely triggering locations in the alpine.

Travel and Terrain Advice
  • Avoid convexities or areas with a thin or variable snowpack.
  • Watch for whumpfing, hollow sounds, and shooting cracks.

Avalanche Problem 2: Wind Slabs

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

Windslabs were created over the last week with 40cm of snow and West winds. The incoming snow coupled with moderate West winds may build sensitive new storm / windslabs.

Travel and Terrain Advice
  • Watch for shooting cracks or stiffer feeling snow. Avoid areas that appear wind loaded.
  • If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.

Avalanche Summary

On Monday a sz 3 natural slab avalanche was observed from a thin snowpack area in the Maligne valley on the NE side of Proposal peak at 2500m. Notable avalanches this past week were generally windslabs in the alpine to sz 2.5 and a few persistent slabs in the low alpine and treeline elevation band.

Snowpack Summary

Moderate SW winds will add the new snow to last week's windslabs in the usual lee locations. Mid-pack persistent weak layers, most notably Jan 7 surface hoar down 40-60cm and rotten Dec 15 facets sitting just below, remain the primary snowpack concern for larger avalanches.

Weather Forecast

Warm, wet, pacific air is meeting cooler arctic air over the forecast area with snowfall intensifying overnight. This system may bring 25-30mm of precipitation with moderate winds and temperatures near -5C. The snowfall event is expected to last into Friday morning when a ridge dominates with cooler temps and blue skies into the weekend.

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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