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Avalanche Forecast

Archived

Dec 30th, 2021–Dec 31st, 2021

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Kootenay Boundary.

 Conditions in this region are "Tricky" right now. Numerous very large persistent slab avalanches failing on a crust have been reported in recent days.  

Check out the latest Forecasters' Blog for tips on managing the ongoing Persistent Slab problem in this region.

Confidence

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

Weather Forecast

THURSDAY NIGHT: Partly cloudy / Light northwest wind / Low of -25

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

SATURDAY: Mix of sun and cloud / Moderate northwest wind / High of -17

SUNDAY: Cloudy with flurries; 3-5 cm / Strong southwest wind / High of -12

Avalanche Summary

A naturally triggered size 3 persistent slab was reported near Rossland on Wednesday. See MIN. 

A skier triggered size 2 storm slab which stepped-down to the early December crust was also reported at Kootenay Pass on Wednesday.

Explosive control work at Kootenay Pass on Tuesday produced numerous persistent slab avalanches failing on the early December crust, up to size 3.5.

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.

Snowpack Summary

Recent storm totals reached over 100 cm. There is a lot of snow available for transport which will form fresh wind slabs when wind speeds increase to moderate.

A crust formed in early December has been responsible for numerous very large persistent slab avalanches in recent days. The depth of the crust ranges widely from 50-150 cm and is most likely to be triggered in wind affected terrain below ridgetops. 

Nearly all of the recent avalanches have been triggered from shallow spots in the snowpack where the crust is less than 100 cm deep. Avoid steep, rocky slopes with a shallow or thin to thick snowpack.

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

Terrain and Travel

  • 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.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Seek out wind sheltered terrain below treeline where you can avoid wind slabs and find great riding.

Problems

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.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.