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Avalanche Forecast

Archived

Feb 2nd, 2021–Feb 3rd, 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 possible, human triggered probable.

Regions

Cariboos.

Human triggering of large storm slabs remains likely on Wednesday. Storm slabs may be surprisingly large and easy to trigger due to the presence of buried weak layers of surface hoar.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

  

TUESDAY NIGHT: Partly cloudy / Light, west ridgetop wind / alpine low temperature -14 / Freezing level valley bottom.

WEDNESDAY: Mix of sun and cloud / Light, northwest ridgetop wind / alpine high temperature -10 / Freezing level valley bottom.

THURSDAY: Flurries; 5-10 cm. / Strong, west ridgetop wind / alpine high temperature -9 / Freezing level valley bottom.

FRIDAY: Mix of sun and cloud / Strong, northwest ridgetop wind / alpine high temperature -8 / Freezing level valley bottom.Snow; 5-10 cm. / Strong, west ridgetop wind / alpine high temperature -9 / Freezing level valley bottom.

Avalanche Summary

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.

A MIN report from just outside this region in Clemina Creek likely represents the surface hoar layer of concern that we suspect is present in much of the Cariboos. Report HERE.

Note: We currently have very few observations from this region. Please consider sharing what you see by submitting a MIN report.

Snowpack Summary

20-30 cm of new snow brings recent snow totals to 40-60 cm. The recent snow fell with warm temps and moderate southerly winds switching to strong northerly which has increased slab development and reactivity within the new snow. These touchy storm slabs are sitting on a weak layer of surface hoar which has potential to surprise backcountry users by how easily these storm slabs may be triggered and how wide the slabs propagate across slopes. However, the size and distribution of this layer is uncertain. 

A second weak of layer of surface hoar and crust from mid January is 50-110 cm deep and tapers above 1700 m. This layer was last reactive almost 2 weeks ago (Jan 16) in the south of the region near Valemount. It is most suspect in sheltered, open slopes at and below treeline. Deeper in the snowpack, a couple of older persistent weak layers may still be identifiable from late and early December, consisting of surface hoar and a crust with faceted snow and buried anywhere from 70-150 cm deep. Deeper layers may wake up with heavy snow fall and warm temperatures.

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 aware of the potential for human triggerable storm slabs at lower elevations, even on small features.
  • Be careful as you transition into wind affected terrain.

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.