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Avalanche Forecast

Archived

Feb 3rd, 2021–Feb 4th, 2021

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

Regions

South Columbia.

Large storm slabs sitting on a very weak layer of surface hoar continue to be LIKELY to human trigger at ALL elevations on Thursday. Conservative terrain choices will be critical to playing safe out there for the next few days.

Confidence

High - The number, quality, or consistency of field observations is good, and supports our confidence.

Weather Forecast

  

WEDNESDAY NIGHT: Cloudy / Moderate, northwest ridgetop wind / alpine low temperature -12 / Freezing level valley bottom.

THURSDAY: Cloudy with isolated flurries; 0-3 cm. / Moderate, northwest ridgetop wind / alpine high temperature -6 / Freezing level valley bottom.

FRIDAY: Cloudy with isolated flurries; 0-3 cm. / Strong, northwest ridgetop wind / alpine high temperature -5 / Freezing level valley bottom.

SATURDAY: Flurries; 3-5 cm. / Light, west ridgetop wind / alpine high temperature -6 / Freezing level valley bottom.

Avalanche Summary

On Tuesday, numerous natural storm slabs up to size 3 and skier triggered up to size 2.5 were reported on all aspects/elevations throughout the region. These storm slabs were primarily running on a weak layer of surface hoar down 50-80 cm. Additionally, a notable size 3.5 naturally triggered persistent slab avalanche failing on a rain crust buried in early January was reported near Trout Lake. 

 See one of several MIN reports Here and Here.

Touchy storm slabs are sitting on a very weak layer of surface hoar which is likely to be reactive to human triggers. Avalanches may be larger than expected due to the presence of this weak layer.

Snowpack Summary

60-100 cm. of recent snow, warm temperatures, and moderate, southerly winds have formed touchy storm slabs. These storm slabs are sitting on multiple weak layers of surface hoar which have potential to surprise backcountry users by how easily they may be triggered and how wide the slabs propagate across slopes. The first sits below the recent snow and the second is around 10-20 cm. deeper.

The lower snowpack is generally well settled and strong in most areas.

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
  • Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.
  • Be careful as you transition into wind affected terrain.
  • Be aware of the potential for human triggerable storm slabs at lower elevations, even on small features.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.