Avalanche Forecast

Northwest Coastal

Date issued

Nov 25, 2017 - 4:51 PM

Valid until

Nov 26, 2017 - 2:00 PM

Prepared by

cgarritty

Avalanche danger is increasing as new snow and strong winds incrementally load the snowpack. Reports from higher elevations have been limited and it remains essential to supplement this forecast with your own observations and safe travel techniques.

Regular season
Saturday - November 25, 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.

Sunday - November 26, 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.

Monday - November 27, 2017
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

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.

Avalanche Problem 1: Storm Slabs

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

Stormy weather is continuing to build touchy new storm slabs at upper elevations. Slab size and reactivity will increase with elevation. A storm slab release may have the potential to step down to deeper weak layer to produce a very large avalanche.

Travel and Terrain Advice
  • Use conservative route selection, choose moderate angled and supported terrain with low consequence.
  • The new snow will require several days to settle and stabilize.
  • If triggered, storm slabs may step down to deeper layers resulting in large avalanches.

Avalanche Problem 2: Loose Wet

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

As snow stacks up at higher elevations, rain has saturated much of the snowpack below treeline. Danger from loose wet avalanches exists where surface snow remains moist - especially in steep terrain.

Travel and Terrain Advice
  • Be cautious of sluffing in steep terrain, particularly where the debris flows into terrain traps.
  • Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.

Avalanche Summary

Reports from Wednesday included observations of several natural wind slab releases from steep, north-facing alpine terrain in Bear Pass. These were triggered by rain. Reports from Sunday showed evidence of a natural loose wet avalanche cycle focused on steep, low elevation rock slabs along Highway 16 between Terrace and Prince Rupert. Observations of high elevation terrain have been very limited. Please post your observations to the Mountain Information Network (MIN)

Snowpack Summary

Snowpack depths at treeline elevations average about 70-130 cm in the south of the region. Here, an elevation dependant 20-40 cm of new snow from last week's storm now forms the upper snowpack. Moderate to strong alpine winds during and since the storm encouraged the formation of storm slabs in the new snow. These slabs will increase in size and sensitivity in wind-exposed areas. A thick rain crust that formed early last week exists below the new snow and has produced hard results in snowpack tests. Below this crust, two weak layers are noted to have formed during the early season. (October 31 and November 11). The deeper late October layer has produced moderate to hard results in targeted snowpack tests. Beneath it, the bottom 20 cm of the snowpack features loose, sugary crystals that have begun to show signs of improved bonding. Looking further to the north of the region near Ningunsaw, the snowpack is starkly different. Here, much drier, colder early season conditions produced a shallow snowpack composed mainly of weak, sugary snow. Snow depths in this part of the region are largely below threshold depths for avalanching.

Weather Forecast

Sunday: Flurries bringing 5-15 cm of new snow. Moderate to strong south winds. Freezing level to 1000 metres with alpine temperatures of -3.

Monday: Periods of snow bringing approximately 15 cm of new snow, increasing over the day. Strong south winds. Freezing level to 1000 metres with alpine temperatures around -2.

Tuesday: Flurries brining 10-15 cm of new snow. Moderate to strong southwest winds. Freezing level around 1000 metres with alpine temperatures around -2.

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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