Avalanche Forecast

Northwest Coastal

Date issued

Feb 18, 2018 - 4:16 PM

Valid until

Feb 19, 2018 - 2:00 PM

Prepared by

mconlan

Strong outflow winds have created very touchy wind slabs. Be cautious in terrain features where snow has accumulated, as the slabs will likely be easy to trigger.

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

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.

Monday - February 19, 2018
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

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

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.

Avalanche Problem 1: Wind Slabs

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

Strong to extreme winds have produced stiff and touchy wind slabs in lee and cross-loaded features. These slabs will be reactive to both natural and human triggers.

Travel and Terrain Advice
  • Be cautious as you transition into wind-affected terrain; avoid lee and cross-loaded features.
  • Use ridges or ribs to avoid pockets of wind-loaded snow.
  • If triggered, wind slabs may step down to deeper layers, resulting in large avalanches.

Avalanche Summary

Many small to large (size 1 to 2) wind slabs were reported on Saturday in steep alpine and cross loaded terrain. They were reported to have released naturally and by skiers due to rapid wind loading from strong northeasterly winds. A small cornice failure was also noted.

Snowpack Summary

Strong northeast outflow winds have redistributed the 40-60 cm of snow that fell since Tuesday. The winds have produced touchy wind slabs in lee and cross-loaded features at all elevations (as observed in this post and this one). This snow sits on a wide variety of surfaces, including wind-scoured and old wind slabs at higher elevations, a sun crust on steep solar aspects, and facets and surface hoar in sheltered locations at treeline and below treeline elevations. The surface hoar and facets are found around 60 to 110 cm below the surface on all aspects up to elevations of 1400 m.

A deeply buried crust/surface hoar layer from mid-January exists in sheltered areas at treeline and below treeline elevations. Thin spot triggering is the primary concern for this layer.

Weather Forecast

MONDAY: Partly cloudy with increasing cloudiness, moderate northwesterly winds, alpine temperature -9 C, freezing level below valley bottom.

TUESDAY: Mostly sunny, light to moderate northerly winds, alpine temperature near -8 C, freezing level below valley bottom.

WEDNESDAY: Mostly sunny, moderate to strong northerly winds, alpine temperature near -5 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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