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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

Cariboos.

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

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

Weather Forecast

  

WEDNESDAY NIGHT: Cloudy with flurries; 0-3 cm. / Moderate, northwest ridgetop wind / alpine low temperature -15 / Freezing level valley bottom.

THURSDAY: Flurries; 3-5 cm. / Moderate, northwest ridgetop wind / alpine high temperature -7 / Freezing level valley bottom.

FRIDAY: Mostly cloudy / Moderate, northwest ridgetop wind / alpine high temperature -6 / Freezing level valley bottom.

SATURDAY: Cloudy with flurries; 0-3 cm. / Light, northwest ridgetop wind / alpine high temperature -8 / 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. Here is an example of a natural storm slab propagating wider than usual due to 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

40-60 cm. of recent snow fell with warm temperatures 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 from mid January is down around 50-110 cm. and is most prevalent on sheltered, open slopes at treeline and below. 

Deeper in the snowpack, a couple of older persistent weak layers may still be identifiable. Deep persistent weak layers may wake up with heavy snow loading and/or 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.