Avalanche Forecast

Issued: Feb 5th, 2021 4:00PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Persistent Slabs and Wind Slabs.

Avalanche Canada JSmith, Avalanche Canada

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Continued discipline and careful route finding will be required on Saturday to avoid triggering large avalanches on a buried persistent weak layer of surface hoar. This layer has been especially reactive at treeline elevations.

Summary

Confidence

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

Weather Forecast

  

FRIDAY NIGHT: Cloudy / Strong, northwest ridgetop wind / alpine low temperature -14 / Freezing level valley bottom.

SATURDAY: Cloudy with flurries; 3-5 cm. / Light, northwest ridgetop wind / alpine high temperature -10 / Freezing level valley bottom.

SUNDAY: Mix of sun and cloud / Moderate, northwest ridgetop wind / alpine high temperature -14 / Freezing level valley bottom.

MONDAY: Sunny / Light, northwest ridgetop wind / alpine high temperature -20 / Freezing level valley bottom.

Avalanche Summary

Persistent 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. An additional recent MIN showing the same is HERE.

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

Snowpack Summary

Southwest switching to northwesterly winds may form reactive wind slabs on a variety of aspects at treeline and above.

40-60 cm. of recent snow is sitting on a very reactive weak layer of surface hoar which has potential to surprise backcountry users by how easily it may be triggered and how wide the persistent slabs propagate across slopes. Recent avalanches on this layer have primarily been reported at treeline and below.

A second weak of layer of surface hoar from mid January is down around 70-110 cm. and is most prevalent in sheltered, open slopes at treeline and below. 

Deep persistent weak layers can still be found in the lower snowpack. These weak layers are most likely to be triggered from rocky areas with a shallow or thin to thick snowpack.

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.

Problems

Persistent Slabs

An icon showing Persistent Slabs

40-60 cm of recent snow has formed reactive slabs sitting on a persistent weak layer of surface hoar. These slabs may be especially reactive in wind affected terrain.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Likely

Expected Size

1.5 - 2.5

Wind Slabs

An icon showing Wind Slabs

Southwest switching to northwesterly winds may form reactive wind slabs on a variety of aspects at treeline and above.

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1.5 - 2.5

Valid until: Feb 6th, 2021 4:00PM