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Avalanche Forecast

Archived

Mar 5th, 2020–Mar 6th, 2020

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 possible, human triggered probable.
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.

Strong wind and some new snow may form wind slabs. Don't be complacent about the buried weak layer that continues to surprise riders.

Confidence

High -

Weather Forecast

THURSDAY NIGHT: Clear skies, moderate to strong southwest wind, alpine temperature -1 C, freezing level 1700 m.

FRIDAY: Cloudy with snowfall, accumulation 5 to 10 cm, moderate southwest wind, alpine temperature -4 C, freezing level 1400 m.

SATURDAY: Cloudy with snowfall, accumulation 10 cm, light south wind, alpine temperature -5 C, freezing level 1300 m.

SUNDAY: Mix of sun and cloud with isolated flurries, light west wind, alpine temperature -9 C, freezing level 1000 m.

Avalanche Summary

A handful more avalanches were triggered by riders on the February 22 surface hoar layer described in the Snowpack Summary. The avalanches were on west, north and east aspects, they were 20 to 40 cm deep, and they occurred around 1900 to 2300 m. The avalanches were small (size 1 to 1.5) to large (size 2). 

Similar avalanches have been observed in the region for the past week, being generally small to large (size 1 to 2) and between 1800 and 2300 m on northwest to east aspects. This trend is suspected to continue as this layer slowly gains strength.

Snowpack Summary

Strong southwest wind and around 5 to 10 cm of snow may form new wind slabs in lee terrain features on Friday. The most suspect areas will be immediately adjacent to ridgelines.

Around 30 to 50 cm of snow overlies a touchy layer of feathery surface hoar crystals. The layer is most commonly found in open trees (e.g. in this MIN) or sheltered terrain around upper below treeline, treeline, and lower alpine elevations. Check out the latest forecaster blog that offers a deeper dive into these conditions.

The remainder of the snowpack is strong and well-settled.

Terrain and Travel

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

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.