Avalanche Forecast

South Columbia

Date issued

Nov 24, 2017 - 4:30 PM

Valid until

Nov 25, 2017 - 2:00 PM

Prepared by

mconlan

A thick crust has formed near the snow surface at all elevations with limited new snow above it -- be cautious of poor snow quality and newly-formed wind slabs.

Regular season
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

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.

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

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.

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

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?

New snow fell on Thursday and Friday with moderate to strong winds. Wind slabs are expected in lee terrain features.

Travel and Terrain Advice
  • Avoid areas which have been loaded by new snow and wind.
  • Be cautious as you transition into wind affected terrain.

Avalanche Problem 2: Persistent Slabs

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

The likelihood of triggering this deeper layer has decreased with the formation of a surface crust from the rain on Wednesday and Thursday. Caution is advised where the deeper layer was not saturated and where the snowpack is thin.

Travel and Terrain Advice
  • Avoid shallow snowpack areas where triggering is more likely.

Avalanche Summary

Many loose wet avalanches were observed on Thursday. Temperatures cooled down on Friday and wet avalanche activity has quieted down.

We currently have very limited observations in this region; please submit your observations to the Mountain Information Network (MIN).

Snowpack Summary

The depth of the snowpack varies greatly with elevation. Recent reports suggest the average depth is 150 to 200 cm in the alpine, 100-150cm at treeline, and decreasing rapidly below treeline where the primary hazards are rocks, stumps, and open creeks.

10 to 20 cm of new snow and moderate to strong winds may have formed wind slabs at treeline and alpine elevations. The new snow sits on a thick crust formed from the rain that fell to mountain tops on Wednesday and Thursday. The snowpack shrunk with the rain and should be well-settled at all elevations. The major feature in the snowpack is a deeper crust which was formed at the end of October and can be found approximately 100 cm below the snow surface at treeline elevations.

We currently have very limited snowpack observations within this region and it is critical to supplement this information with your own observations.

Weather Forecast

The next wave of precipitation is expected to begin Saturday evening and may transition from snow to rain to snow again.

SATURDAY: Mostly cloudy with isolated flurries, light to moderate southwesterly winds, freezing levels near 1500 m. Snowfall to begin Saturday evening.

SUNDAY: 10-20 mm precipitation throughout the day with snow switching to rain Sunday morning, moderate to strong southerly winds, freezing levels rising to around 2200 m.

MONDAY: A mix of sun and cloud, light to moderate westerly winds, freezing level near 1200 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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