Kootenay Boundary Avalanche Forecast

Issued: Dec 28th, 2021 3:00PM

Wed Dec 29th Current Conditions
Alpine Moderate Treeline Moderate Below Treeline Moderate
Thu Dec 30th 2 Day Outlook
Alpine Moderate Treeline Moderate Below Treeline Moderate
Fri Dec 31st 3 Day Outlook
Alpine Moderate Treeline Moderate Below Treeline Moderate

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

Recently formed storm slabs will be most reactive to human triggers in wind affected terrain.

A persistent slab problem has created a low likelihood, high consequence scenario that is best avoided through conservative terrain choices.

Summary

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

TUESDAY NIGHT: Partly cloudy / Light north wind / Low of -24

WEDNESDAY: Sunny / Light north wind increasing to moderate in the afternoon / High of -17

THURSDAY: Mix of sun and cloud / Light to moderate northwest wind / High of -17

FRIDAY: Sunny / Light northeast wind / High of -17

Avalanche Summary

A rider triggered size 2.5 persistent slab avalanche involving several riders was reported near Nelson on Monday. The avalanche occurred on a southeast aspect at approximately 1900 m. It failed on the crust formed in early December. The treeline slope was heavily wind effected and the rider triggered the avalanche from a thin spot where the layer was only around 60 cm deep. There is a MIN report of the incident.

Additionally, several natural and human triggered storm slab avalanches up to size 2.5 were reported on all aspects and elevations on Monday. An example of a skier triggered storm slab near Rossland can be found in a MIN report HERE.

Snowpack Summary

Recent storm totals reached over 100 cm. Expect dry loose avalanches (sluffing) running far and fast in steep terrain. There is a lot of snow available for transport which will form fresh wind slabs when wind speeds increase to moderate.

The recent snow reportedly covered a thin freezing rain crust and a surface hoar interface, which has been responsible for recent storm slab avalanches. For now, we don't expect the new snow to bond well to the old interface. 

A crust from early December is now 50-120 cm below the surface, and is found up to 2300 m. A layer of weak facets (sugary snow) has been reported above and below this crust, and is the layer of concern in our persistent avalanche problem.

The lower snowpack is composed of several early-season crusts. Snow depths at treeline average 150-300 cm.

Terrain and Travel

  • Use small low consequence slopes to test the bond of the new snow.
  • Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
  • Seek out wind sheltered terrain below treeline where you can avoid wind slabs and find great riding.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

Problems

Storm Slabs

An icon showing Storm Slabs

Likelihood

Possible

Expected Size

1.5 - 2.5

The recent snow may become more reactive to human triggers as it settles into a more cohesive slab. Look for signs of instability: whumpfing, hollow sounds, shooting cracks, and recent avalanches. 

Aspects:

All aspects.

Elevations:

All elevations.

Persistent Slabs

An icon showing Persistent Slabs

Likelihood

Possible

Expected Size

2 - 3

A persistent slab problem formed by a crust down 50-150 cm has created a low likelihood, high consequence scenario that is difficult to forecast. This layer is most likely to be triggered in windy areas where the depth of the snowpack is highly variable.

Avoid likely trigger spots such as steep, rocky or convex slopes with a shallow or thin to thick snowpack. 

Aspects:

All aspects.

Elevations:

All elevations.

Valid until: Dec 29th, 2021 3:00PM

Forecast Trend

The latest forecast danger ratings, broken down to elevation. See how an elevation is trending.