Avalanche Forecast

Northwest Coastal

Date issued

Feb 20, 2018 - 3:49 PM

Valid until

Feb 21, 2018 - 2:00 PM

Prepared by

mconlan

Wind slabs linger at higher elevations. With a warming trend and clear skies, watch out on solar aspects where the sun could weaken the snow surface.

Regular season
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.

Wednesday - February 21, 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.

Thursday - February 22, 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 winds produced stiff and touchy wind slabs in lee and cross-loaded features. These slabs may be reactive to human triggers and could weaken with warmer air temperatures and the sun's influence.

Travel and Terrain Advice
  • Look for signs of instability: whumpfing, hollow sounds, shooting cracks, and recent avalanches.
  • 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.

Avalanche Summary

A few wind slab avalanches were reported on Monday, being triggered naturally and by heavy loads.  They were small to large (size 1.5 to 2), up to 1500 m in elevation, and up to 1 m deep.  Many small to large (size 1 to 3.5) wind slabs were reported on both Saturday and Sunday in lee features and cross-loaded terrain on southerly to easterly slopes.  The avalanches were triggered naturally and by skiers.

Avalanche activity may increase with warmer air temperatures and forecasted clear skies. Watch for steep sunny slopes due to the sun’s influence, lee features for reactive wind slabs, and be extra cautious near thin spots and shallow snow pack areas where triggering a deeper weak layer is more likely.

Snowpack Summary

Strong northeast outflow winds redistributed the 40-60 cm of storm snow from last week and weekend.  The winds produced touchy wind slabs in lee and cross-loaded features.  The recent cold temperatures are helping to break down these wind slabs, but stiff slabs will likely remain reactive to light and heavy loads where preserved. 

The wind slabs sit 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 facet layers are found around 20 to 40 cm as well as 60 to 110 cm deep and on all aspects and elevation bands.

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

WEDNESDAY: Cloudy early morning with trace snowfall then mostly sunny, moderate to strong northerly winds, alpine temperature near -5 C, freezing level below valley bottom.

THURSDAY: Partly cloudy with increasing cloudiness, light to moderate northwesterly winds, alpine temperature -4 C, freezing level below valley bottom.

FRIDAY: Cloudy with early-morning snowfall, accumulation 10-15 cm, light to moderate westerly winds, alpine temperature near -3 C, freezing level near 500 m.

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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