Avalanche Forecast

Northwest Coastal

Date issued

Feb 13, 2018 - 5:22 PM

Valid until

Feb 14, 2018 - 2:00 PM

Prepared by

mgrist

Avalanches will remain very likely in the wake of Tuesday's massive storm. Avoid all avalanche terrain, free from overhead hazard.

Regular season
Tuesday - February 13, 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

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.

Wednesday - February 14, 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

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.

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.

Avalanche Problem 1: Storm Slabs

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

Heavy snowfall and strong to extreme winds are a recipe for rapid loading and widespread avalanches.... it's a good time to avoid all avalanche terrain!

Travel and Terrain Advice
  • If triggered the storm slabs may step down to deeper layers resulting in large avalanches.
  • Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
  • The new snow will require several days to settle and stabilize.

Avalanche Problem 2: Persistent Slabs

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

A weak layer exists 120-150 cm below the surface. It may still be possible for humans to trigger persistent slab avalanches on this layer, or for a storm slab release to step down to this layer resulting in a very large avalanche.

Travel and Terrain Advice
  • Avoid lingering in runout zones. Large avalanches may run long distances.
  • Minimize overhead exposure during periods of heavy loading from new snow, wind.
  • Caution around convexities or areas with a thin or variable snowpack.

Avalanche Summary

We haven't received reports (yet) but we anticipate a widespread natural avalanche cycle occurred on Tuesday.

Snowpack Summary

Phenomenal snowfall amounts occurred on Tuesday, with 40-50cm falling in a 12 hour period near Terrace! Combine that with strong north west winds and temperatures near zero... it's a perfect recipe for widespread large destructive avalanches.

All this new snow sits on a wide array of surfaces - either wind scoured from strong and variable winds from the long weekend, or fresh wind slabs at higher elevations on lee (downwind) slopes.

Beneath the storm snow lies a 5-20 cm thick crust that was buried early February and can be found 60-110 cm below the surface on all aspects up to 1400 m.

A weak layer buried in mid-January is 120-150 cm below the surface and remains a concern. In most areas this layer is a crust, but it may also be surface hoar in sheltered areas at tree line and below. This layer may remain reactive as it adjusts to the weight of the new snow.

In thinner snowpack areas (north and inland), deeper crust / surface hoar layers that were buried in December and early January may still be a concern. They are buried over 150 cm below the surface, but could still be reactive and triggered from shallow spots.

Weather Forecast

We'll have unsettled conditions in the wake of Tuesday's awesome storm.

WEDNESDAY: Cloudy. Ridge wind moderate to strong from the north / west. Temperature -5. Freezing level 400m.

THURSDAY: Snow in the afternoon (5cm). Ridge wind strong from the west. Temperature -6. Freezing level valley bottom.

FRIDAY: Cloudy. Ridge wind moderate to strong from the north / west. Temperature -5. Freezing level 400m.

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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