Avalanche Forecast

Issued: Jan 1st, 2021 4:00PM

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

Avalanche Canada JSmith, Avalanche Canada

  

Continued reports of human triggered persistent slab avalanches are keeping hazard elevated in this region. Small wind slabs in motion may trigger much larger persistent slab avalanches.

Summary

Confidence

Moderate - Uncertainty is due to the limited number of field observations. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

  

FRIDAY NIGHT: Snow; 5-10 cm. / Strong, southwest ridgetop wind / alpine low temperature -9 / Freezing level 1000 m.

SATURDAY: Snow; 5-10 cm. / Strong, southwest ridgetop wind / alpine high temperature -5 / Freezing level 1400 m.

SUNDAY: Snow; 5-15 cm. / Strong, southwest ridgetop wind / alpine high temperature -4 / Freezing level 1500 m.

MONDAY: Cloudy with flurries; 3-5 cm. / Moderate, west ridgetop wind / alpine high temperature -7 / Freezing level 1200 m.

Avalanche Summary

On Thursday, a ski cut resulted in a size 2 persistent slab avalanche on a northeast aspect in the alpine near Kicking Horse Mountain Resort. MIN report HERE.

A skier triggered avalanche was reported in the Golden area on Wednesday. Check out the MIN report HERE. The 50 cm failure plane depth matches up with the persistent weak layers discussed in our snowpack summary. The report also suggests that in some areas more recent wind slabs may be quite reactive.

These recent avalanches are a reminder that when persistent slabs are the problem; conservative terrain choices are the answer.

Snowpack Summary

A skiff of new snow has buried a new layer of surface hoar in many parts of the region. This will be a key interface to watch as new snow piles up over the weekend.

Also at the surface, winds blowing from a variety of directions last week formed wind slabs in lee features at treeline and above.

There are currently several critical layers of concern. The early December surface hoar is down 30 to 80 cm. It has recently been sensitive to remote triggering which is well illustrated in this MIN post from the Golden area.

Below, or near the surface hoar you may encounter a crust. This crust has been observed as high as 2400 m. in the south of the region and 1800 m. in the north.  

The lower snowpack is characterized by more crusts, the most notable is a rain crust from early November that is 50 to 130 cm deep. This crust is sitting near the base of the snowpack, surrounded by a weak layer of sugary facets. It is most likely to be reactive to human triggers in steep, shallow, rocky areas with a thin to thick snowpack.

Terrain and Travel

  • Uncertainty is best managed through conservative terrain choices at this time.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
  • Remote triggering is a concern, watch out for adjacent and overhead slopes.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

Problems

Wind Slabs

An icon showing Wind Slabs

Small wind slabs in motion may step down to deeper weak layers, resulting in large avalanches.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs

A weak layer of surface hoar down 50-100 cm. has been reactive to human triggers, resulting in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3

Deep Persistent Slabs

An icon showing Deep Persistent Slabs

A Crust buried near the bottom of the snowpack has been responsible for some very large explosive triggered avalanches up to size 4.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2.5 - 4

Valid until: Jan 2nd, 2021 4:00PM