Avalanche Forecast

North Columbia

Date issued

Mar 11, 2018 - 4:57 PM

Valid until

Mar 12, 2018 - 2:00 PM

Prepared by

mgrist

Avalanche danger will increase in the afternoon with strong solar input and warming temperatures. Concern for persistent slab problems is on the rise.
See the Forecaster's Blog for more: http://www.avalanche.ca/blogs/2018-03-09-first-big-warm-up

Regular season
Sunday - March 11, 2018
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.

Monday - March 12, 2018
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.

Tuesday - March 13, 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

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: Loose Wet

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

Wet loose avalanches are likely in steep, rocky, sunny terrain. Warming could also wake up more deeply buried weak layers, creating a surprisingly large avalanche.

Travel and Terrain Advice
  • Be cautious of sluffing in steep terrain, particularly where the debris flows into terrain traps.
  • Avoid exposure to sunny slopes, especially in the afternoon.

Avalanche Problem 2: Wind Slabs

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

Wind slabs formed on all aspects during the recent storm and they may remain reactive on Monday. Extra caution is needed on solar aspects where sunshine could act as a natural trigger and buried sun crust as a sliding layer.

Travel and Terrain Advice
  • Watch for wind loaded pockets near ridge crests and roll-overs.
  • Use ridges or ribs to avoid pockets of wind loaded snow.
  • Use caution on open slopes and convex rolls

Avalanche Problem 3: Persistent Slabs

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

Rising temperatures and strong sunshine are increasing concern for weak layers buried deep in the snowpack. In addition to human triggering in thin spots, solar warming and cornice releases are possible natural triggers for persistent slabs.

Travel and Terrain Advice
  • Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.
  • Pay attention to overhead hazards like cornices which could trigger persistent slabs.
  • Avoid convoluted terrain with variable snow depths and multiple trigger points.

Avalanche Summary

A widespread natural avalanche cycle to size 3 was reported on Saturday. These avalanches were primarily wet loose avalanches on sunny aspects, however, some did step down to the mid-February layer on southerly aspects.

Reports from Friday included observations of numerous storm slabs and wind slabs that ran from size 1.5 to 2.5. These were triggered naturally as well as with ski cutting and all aspects and elevations were represented.

Avalanche activity is expected to increase as we move into a period of intense sun and prolonged warming. Predictable loose wet avalanches from steep, sunny terrain should be easy to manage. A trickier problem will emerge as warmth penetrates into the snowpack to tickle deeper persistent weak layers. This will be a time to avoid exposure to large sunny features and keep well away from corniced slopes.

Snowpack Summary

15-25 cm of snow from Thursday into Friday sits on sun crusts on solar aspects and well-settled storm snow on more northerly aspects. Several other sun crust layers may be found within the older storm snow on solar aspects.

A couple of layers buried in mid to late February (down around 60-110 cm) are variably reactive, but both have the potential to create surprisingly large avalanches if triggered. Initially, these interfaces were most reactive on solar aspects, where they present as buried sun crusts. However, persistent slabs have been triggered on shady aspects too, where surface hoar and/or facets exist.

Deeper persistent weak layers from January and December are generally considered dormant, but could wake up with forecast warming, a surface avalanche stepping down, cornice fall, or a human trigger in a shallow or variable-depth snowpack area. These layers consist of sun crust, surface hoar and/or facets.

Weather Forecast

Sunny and warm until the start of our next weather system on Wednesday.

MONDAY: Sunny. Light southeast winds. Freezing level rising to 2200 metres with alpine high temperatures around +2.

TUESDAY: Mainly sunny. Light southeast winds, increasing over the day. Freezing level to 2500 metres with alpine high temperatures of +3.

WEDNESDAY: Cloudy with isolated flurries in the afternoon. Light south winds. Freezing level near 2000 metres with alpine high temperatures of +1.

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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