Cariboos Avalanche Forecast

Mar 13th, 2020 4:00PM

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

Strong northeast wind will continue to form fresh wind slabs on previously windward slopes. Be prepared for unusually cold temperatures for this time of year when venturing out.

Summary

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

Friday night: Mostly clear, strong northeast wind, alpine high temperature -28 C, freezing level at valley bottom.

Saturday: Mostly sunny, moderate northeast wind, alpine high temperature -20 C, freezing level at valley bottom.

Sunday: Sunny, light northerly wind, alpine high temperature -15 C, freezing level at valley bottom.

Monday: Sunny, light westerly wind, alpine high temperature -10 C, freezing level at 900 m.

Avalanche Summary

A natural avalanche cycle occurred most likely during the storm on Tuesday with avalanches up to size 3. 

Many large to very large avalanches (size 2-3) releasing on the February 22 surface hoar have been observed up to a week ago. These avalanches primarily occurred on north, northeast, and east aspects between 1400-2100 m and in the southern part of the region. Characteristics of these avalanches included remote-triggers, wide propagation, and a false sense of stability from unreactive ski cuts or from multiple people moving through the terrain before avalanches released. This MIN from a large, snowmobile-triggered avalanche Friday a week ago is a helpful example. Even though avalanche observations on this weak layer decreased in the past week this layer might still be reactive to human triggers. 

Snowpack Summary

The recent storm delivered 20-60 cm with strong southerly winds which now shifted to northeast. The snow surface varies from soft snow to wind pressed at upper elevations. 

A weak layer of surface hoar may be found 50-100 cm deep. Reports indicate that this layer may be absent in the northern tip of the region (see this MIN from Sugarbowl). However, observers have identified the layer in snow profiles from Barkerville to Valemount (see this MIN from Mt Greenbury, this MIN from the Trophy Mountains, and this MIN from Allan Creek). Sheltered north, northeast, and east facing slopes near treeline are the most suspect.

This persistent slab problem is transitioning into a low probability/high consequence scenario. The snow above the weak layer has increased in depth and slab properties, making avalanches more difficult to trigger and masking obvious clues that the problem is present (i.e. cracking, whumpfing). However, if triggered, avalanches will be large and getting caught could have serious consequences. Managing this problem requires a patient and diligent mindset, implemented by avoiding suspect slopes and maintaining conservative terrain margins. This persistent weak layer will likely pose the threat of a low probability/high consequence avalanche until there is a substantial change in the snowpack. Read more about surface hoar on our forecaster blog.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.

Problems

Wind Slabs

An icon showing Wind Slabs

Likelihood

Likely

Expected Size

1 - 2

Moderate to strong northeast wind will continue to form fresh wind slabs at all elevations. The wind shifted recently and is transporting snow onto previously windward slopes. Wind slabs will be reactive to human triggering. 

Aspects:

East, South East, South, South West, West, North West.

Elevations:

All elevations.

Persistent Slabs

An icon showing Persistent Slabs

Likelihood

Unlikely-Possible

Expected Size

1.5 - 3

A weak layer of surface hoar is buried 50-100 cm deep. Even though avalanche reports decreased over the past week it might still possible to human-trigger. Up to a week ago, large (size 2-3) natural and human-triggered avalanches have released on this layer. Observations were concentrated to north, northeast, and east aspects near treeline. This problem has been observed in all but the northern tip of the region, where there is uncertainty around the distribution of this layer.

Aspects:

All aspects.

Elevations:

All elevations.

Valid until: Mar 14th, 2020 5:00PM