Avalanche Forecast

North Columbia

Date issued

Jan 30, 2018 - 5:09 PM

Valid until

Jan 31, 2018 - 2:00 PM

Prepared by

mgrist

Conditions remain primed for human-triggered avalanches. Give the snowpack time to settle before pushing into more aggressive terrain: Simple terrain is recommended for now.

Regular season
Tuesday - January 30, 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.

Wednesday - January 31, 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.

Thursday - February 1, 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.

Avalanche Problem 1: Storm Slabs

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

Warming temperatures put heavier snow on top of lighter dry snow - a recipe for an unstable snowpack. A storm slab could step down to a deeper weak layer, creating a surprisingly large avalanche.

Travel and Terrain Advice
  • The new snow will require several days to settle and stabilize.
  • Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.
  • Be wary of slopes that did not previously avalanche.

Avalanche Problem 2: Persistent Slabs

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

Several weak layers are buried in the snowpack, creating very large avalanches when triggered.

Travel and Terrain Advice
  • Avoid open slopes and convex rolls where buried surface hoar may be preserved.
  • Avoid steep convexities or areas with a thin or variable snowpack.
  • Make conservative terrain choices.

Avalanche Summary

On Tuesday we received preliminary reports of an avalanche involvement in the north of the region near Clemina creek. The information we have indicates the avalanche ran on a north facing aspect near 1900m.

A widespread natural avalanche cycle to Size 4 was reported on Tuesday, at all elevations and aspects. Many large avalanches were running on the mid December persistent weak layer, down approximately 150cm.

On Saturday, a human-triggered Size 2.5 avalanche was reported near 2300m on a south west aspect in Glacier National Park. See the MIN report for incident details.

Conditions will remain primed for human triggered avalanches, with the potential for some surprisingly large avalanches given how many persistent weak layers exist in the snowpack.

Snowpack Summary

60-90 cm of snow fell from Sunday through to Tuesday and temperatures warmed up to -1 at tree line on Monday. Winds were strong to extreme from the south, building cornices and creating wind slabs on lee (down wind) slopes.

The new snow sits on a complex snowpack and there are three main weak layers that professionals are monitoring:

1) 80-110 cm of storm snow sits on a crust and/or surface hoar layer from mid-January. The crust is reportedly widespread, with the possible exception of high elevation north aspects. The mid-January surface hoar is 5 to 20 mm in size and was reported at tree line elevations and possibly higher.

2) Deeper in the snowpack, the early-January persistent weak layer is 110 to 140 cm below the surface. It is composed of surface hoar on sheltered slopes as well as sun crust on steep solar aspects and is found at all elevation bands. Snowpack tests show sudden fracture characters and signs of instability such as whumpfs, cracking and avalanches.

3) Another weak layer buried mid-December consisting of a facet/surface hoar/crust combination is buried 120 to 170 cm deep. It is most problematic at and below tree line.

Weather Forecast

Wednesday: Isolated flurries (up to 5cm possible). Light southerly winds. Alpine temperature near -5.

Thursday: 5-10 cm snow. Moderate south west winds. Alpine temperature -6.

Friday: 10-15cm of snow. Moderate south west winds. Alpine temperature near -5.

More information can be found in the Mountain Weather Forecast.

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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