Avalanche Forecast

Northwest Coastal

Date issued

Nov 23, 2017 - 6:06 PM

Valid until

Nov 24, 2017 - 2:00 PM

Prepared by

cgarritty

Although forecast confidence is low, there is certainty that recent heavy snowfall and ongoing loading is elevating avalanche danger in the region. Please post your observations to the Mountain Information Network. (MIN)

Regular season
Thursday - November 23, 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

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.

Friday - November 24, 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

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.

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

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.

Avalanche Problem 1: Storm Slabs

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

Recent stormy weather likely formed thick new storm slabs at upper elevations. These are expected to remain reactive over the near term. 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 stacked up at higher elevations, rain saturated 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.
  • Use extra caution on steep slopes if the snow is moist or wet.

Avalanche Summary

No new avalanche activity has been reported, but this lack of information does not represent benign conditions. Watch for the presence and sensitivity of storm slabs to increase with elevation and please post your observations to the Mountain Information Network (MIN)

Snowpack Summary

50-60 mm of precipitation fell over the region over Wednesday, accompanied by moderate to strong winds and freezing levels around 800 metres. Under these conditions, new snow accumulations of up to 60 cm may now form our upper snowpack at upper elevations. New snow depths and wind effect will increase with elevation. Although the composition of the mid and lower snowpack in the region is uncertain, rapid loading of the upper snowpack carries the potential to activate weaker layers that are likely to have formed during the early season.

Weather Forecast

Thursday night: Flurries bringing approximately 10 cm of new snow. Moderate to strong southwest winds.

Friday: Flurries bringing 5-15 cm of new snow. Strong to extreme southwest winds. Freezing level to 800 metres with alpine temperatures around -4.

Saturday: Continuing flurries bringing 10-15 cm of new snow. Moderate to strong southeast winds. Freezing level to about 700 metres with alpine temperatures around -3

Sunday: Scattered flurries bringing 5-10 cm of new snow Moderate to strong south winds. Freezing level to about 700 metres with alpine temperatures of about -5.

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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