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Avalanche Forecast

Archived

Jan 8th, 2021–Jan 9th, 2021

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Columbia.

Don't let sunny skies and good snow lure you into complex terrain. Recent human triggered avalanches have been large. Avalanche danger may be improving as the likelihood of triggering them diminishes, but if you're unlucky enough to do so, consequences can be high.

Confidence

High - The number, quality, or consistency of field observations is good, and supports our confidence. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Friday night: Partly cloudy, light west wind, freezing level valley bottom.

Saturday: A mix of sun and cloud, light southeast wind, alpine high -7, freezing level valley bottom.

Sunday: Increasing cloud, light southeast wind, alpine high -7, freezing level valley bottom.

Monday: Flurries, trace, light to moderate southeast wind, alpine high -6, freezing level 800 m.

Avalanche Summary

Recent avalanche activity has been widespread, large (size 2+), running on a variety of weak layers and triggered both naturally and by humans.

  • Natural storm/wind slab - Numerous natural storm/wind slab avalanches have been observed in the last few days on all aspects at alpine and treeline elevations, averaging size 2.

  • Human triggered - Thursday and Friday were eventful days for human triggered avalanches in the busiest areas of the region. RMR slackcountry saw four size 1.5-2 skier triggered avalanches, including a partial burial. Check out some of these MIN reports here, here and here. Crowns ranged from 30 to 70 cm, likely running on the most recent storm interface at the shallow end, and on the Christmas persistent layer at the deeper end.

  • Persistent slab - On Wednesday and Thursday, there were four natural persistent slab avalanches size 2.5-3 reported in the region on northerly aspects in the alpine. Three of these were reported to have run on the early December persistent weak layer.

Snowpack Summary

Around 40-80 cm of recent snow sits on a weak layer of surface hoar that was buried around Christmas. This layer is most prevalent at and below treeline. Previous moderate to strong winds have redistributed surface snow, creating wind slabs at wind exposed elevations.

A couple of persistent weak layers buried in early/mid-December are down about 90-150 cm. Generally, they can be found as a layer of surface hoar above in close proximity to a crust/surface hoar layer. The form and distribution of these layers are highly variable and conditions may differ significantly from one valley to the next. 

Terrain and Travel

  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
  • Avalanche hazard may have improved, but be mindful that deep instabilities are still present.
  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.