Avalanche Forecast

North Columbia

Date issued

Jan 6, 2018 - 4:42 PM

Valid until

Jan 7, 2018 - 2:00 PM

Prepared by

mconlan

New snow is falling on numerous weak layers. As the snow gains slab properties, natural and human-triggered avalanches will become more likely. Assess the upper snowpack to observe for these slab properties. Cautious route finding is advised.

Regular season
Saturday - January 6, 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

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 - January 7, 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

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 - January 8, 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: Persistent Slabs

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

Around 40 to 80 cm of snow sits above two weak layers. As this snow continues to settle and gains slab properties, a dangerous slab that is easily triggered may form.

Travel and Terrain Advice
  • Avoid open slopes and convex rolls at treeline where buried surface hoar may be preserved.
  • Watch for signs of slab formation, such as whumpfing and shooting cracks.
  • Use conservative route selection. Choose moderate-angled and well-supported terrain.

Avalanche Problem 2: Storm Slabs

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

Up to 20 cm of new snow is sitting on variable surfaces and may not bond well to them. Slab avalanches may form when the new snow gains slab properties. The snow may have fallen with elevated winds in the alpine, so be cautious entering lee features.

Travel and Terrain Advice
  • Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.
  • Use caution when entering lee areas. Recent wind loading may have created wind slabs.

Avalanche Summary

Recent natural, skier-triggered, snowmobile-triggered, and skier-remoted avalanches have been reported on the December 15 layer at and below treeline on all aspects.  The avalanches were generally small, being reported between size 1 and 2.  Numerous reports of whumphing were also noted in low elevation cutblocks and flat terrain.

Sluffing was also noted within the new snow in steep terrain.  Reactivity of the storm and persistent slabs are likely to increase as the upper snowpack forms slab properties.

Snowpack Summary

10-15 cm of new snow fell on surface hoar in sheltered slopes and a sun crust on steep solar aspects and may not bond well to them.  The snow also may have fallen with moderate southwesterly winds in the alpine, which could have produced small wind slabs in lee features.

The additional snow could create a dangerous slab above buried weak layers.  Numerous persistent weak layers exist in the snowpack.  Dry snow overlies two layers composed of weak and feathery surface hoar, with the deeper layer (December 15) buried 40 to 80 cm.  This layer is found most often around and below treeline.  As the overlying dry snow becomes more cohesive and forms a slab, this layer has the potential to create easily-triggerable destructive slab avalanches.  Snowpack tests are showing that this layer could form avalanches (i.e. sudden fracture characters, high propagation potential, whumpfing, rutschblock 1 to 3). 

Deeper in the snowpack (90 to 150 cm), a November crust is producing variable test results, from sudden to no result.  This layer is considered dormant but could be triggered where the snowpack is thin.

Please share your recent observations through the Mountain Information Network.

Weather Forecast

SUNDAY: Cloudy with light snowfall, accumulation 5-15 cm, moderate southwesterly winds increasing over the day, alpine temperature near -7 C, freezing level near 800 m.

MONDAY: Cloudy with light snowfall, accumulation 5-10 cm, light to moderate southwesterly winds, alpine temperature near -5 C, freezing level near valley bottom.

TUESDAY: Cloudy with light snowfall, accumulation 10-20 cm, light to moderate southwesterly winds, alpine temperature near -6 C, freezing level near valley bottom.

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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