Avalanche Forecast

South Coast Inland

Date issued

Dec 21, 2017 - 4:14 PM

Valid until

Dec 22, 2017 - 2:00 PM

Prepared by

jmcbride

Hazard ratings are for the southern part of the region where storm snow totals range from 80-100 cm.  Northern areas that received lower snowfall amounts (25-35 cm) can expect the same avalanche problems with lower hazard ratings.

Regular season
Thursday - December 21, 2017
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.

Friday - December 22, 2017
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 - December 23, 2017
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: Wind Slabs

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

Outflow (northerly) winds have redistributed the recent storm snow building wind slabs on leeward slopes.

Travel and Terrain Advice
  • Watch for signs of instability such as whumpfing, or cracking.
  • Choose moderate angled and supported terrain with low / no consequence.
  • If off-trail travel is deep and punchy, avoid avalanche terrain, including runouts.

Avalanche Problem 2: Loose Dry

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

It may be possible to trigger a storm snow release in steep or convex, non wind-affected areas.

Avalanche Summary

The Coquihalla and Allison Pass areas reported numerous loose dry to Size 1.5, as well as slab and glide avalanches to Size 2 on steep, leeward terrain and smooth rock slabs on Wednesday, while reports from the northern part of the region indicated wind slab activity up to size 2 on north and west aspects in the alpine.

On Tuesday the northern part of the region saw several skier controlled avalanches to Size 1 in both hard and soft wind slabs at treeline as well as significant wind loading (up to 60 cm) and cracking on open slopes.

In the southern part of the region no new avalanches have been observed, however classic signs of instability such as whumpfing and shooting cracks have been reported here in the MIN.

Snowpack Summary

The recent storm snow has been redistributed by moderate to strong northerly winds in the alpine and exposed treeline areas, creating wind slabs in some areas and scouring others (particularly in the northern part of the region).The southern part of the region has seen impressive storm snow totals (80-100cm) since Sunday night, compared to northern areas of the region, which received 25-35cm. This new snow sits on crusts of variable thickness that formed on almost all aspects in mid-December (December 15th layer). On steep southerly aspects the crust is supportive, whereas on northerly aspects the crust is quite thin and variable. Beneath the December 15th layer the snowpack is well settled and has not been showing any signs of activity on the late November rain crust which is now buried 50-80 cm in the northern part of the region and well over 1 m in the south.

Weather Forecast

FRIDAY: Mix of sun and cloud, light flurries. Accumulation trace. Ridge wind light to moderate from the northeast. Temperature -10. Freezing level surface.

SATURDAY: Mostly sunny. Ridge wind light from the northeast. Temperature -10. Freezing level surface.

SUNDAY: Cloudy, flurries. Accumulation up to 5 cm. Ridge wind light from the southeast. Temperature -12. Freezing level surface.

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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