Avalanche Forecast

Northwest Coastal

Date issued

Feb 15, 2018 - 5:03 PM

Valid until

Feb 16, 2018 - 2:00 PM

Prepared by

jmcbride

Large cornices and storm slabs have formed following Tuesday's big storm event. Reactivity of these may increase if the sun starts to pack a punch, especially on solar and leeward aspects.

Regular season
Thursday - February 15, 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.

Friday - February 16, 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.

Saturday - February 17, 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.

Avalanche Problem 1: Storm Slabs

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

Recent heavy snowfall and strong winds have formed widespread storm slabs. At treeline and below these slabs overlie recently buried surface hoar and have been reactive to light triggers.

Travel and Terrain Advice
  • Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Use caution on open slopes and convex rolls at treeline where buried surface hoar may be preserved.
  • Give cornices a wide berth when travelling on or below ridges.

Avalanche Summary

There were no new reports of avalanches on Thursday.

A widespread natural avalanche cycle up to size 3.5 was reported on Wednesday following the intense loading from new snow and wind, with at least one avalanche running beyond it's historical runout distance.

Explosive control work on Wednesday produced numerous storm slab releases up to size 2.5, at all elevations. At lower elevations, treeline and below, these slabs were failing on a layer of surface hoar buried by the storm snow on Tuesday.

Large cornices have formed as a result of continued moderate, westerly winds and Tuesday's storm event.  Expect these to be weak particularly with daytime warming and sunny weather.

Snowpack Summary

Approximately 40-60 cm of new snow has fallen across the region since Tuesday with the highest snowfall amounts in the Terrace area.

This new snow sits on a wide array of surfaces - including wind scoured from strong and variable winds during the long weekend, and fresh wind slabs at higher elevations on lee (downwind) slopes, as well as facets and surface hoar in sheltered locations at treeline and below, and suncrusts on steep solar aspects.

Also a 5-20 cm thick crust/surface hoar layer that was buried early February and can be found 60-110 cm below the surface on all aspects up to 1400 m.

In thinner snowpack areas (north and inland), a deeper crust / surface hoar layer that was buried in mid-January in sheltered areas at treeline and below could still be a concern for triggering from shallow spots.

Weather Forecast

TONIGHT: Cloudy, flurries. Accumulation up to 5 cm. Ridge wind moderate, west. Temperature -5. Freezing level 500 m.

FRIDAY: Mix of sun and cloud. Ridge wind light, south. Temperature -7. Freezing level 300 m.

SATURDAY: Mix of sun and cloud, light flurries. Accumulation trace. Ridge wind moderate to strong, northeast. Temperature -12. Freezing level valley bottom.

SUNDAY: Sunny. Ridge wind moderate, northeast. Temperature -12. 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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