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Avalanche Forecast

Archived

Mar 9th, 2020–Mar 10th, 2020

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
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.

A swift uptick in winds should put increasing wind slab hazards at top of mind for Tuesday. Keep your guard up around steep, sheltered slopes where persistent slabs are a lingering concern.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Monday night: Clear. Light southwest winds increasing to moderate by morning.

Tuesday: Becoming cloudy with increasing flurries bringing 5-10 cm of new snow by end of day, continuing but easing overnight. Moderate to strong southwest winds. Alpine high temperatures around -6.

Wednesday: Decreasing cloud with final flurries leaving up to 5 cm of new snow. Light northwest winds. Alpine high temperatures around -8.

Thursday: Mainly sunny. Light west winds. Alpine high temperatures around -10.

Avalanche Summary

Reportd from Saturday and Sunday showed numerous natural, skier triggered and explosives controlled storm slab avalanches reaching size 1 to 2 on all aspects between 1900 and 2100 m. A gradual trend toward artificial triggers is evident in reports, as well as improving visibility allowing observation of earlier releases. These avalanches were generally limited to the depth of new snow, reaching up to 40 cm deep.

On Friday, a few small (size 1.5) avalanches released on the February surface hoar layer described in our Snowpack Summary. They occurred on northerly aspects around 2000 m and were 20 to 30 cm deep. 

Over the past two weeks, small to large (size 1 to 2) avalanches have released on this surface hoar layer. They have most often released between 1800 and 2300 m on northwest to east aspects. This trend is suspected to continue as this layer slowly gains strength.

Snowpack Summary

Around 10-15 cm of snow fell in the west of the region and 20 to 35 cm in the east of the region over the weekend. Storm slabs are likely developing as the snow consolidates. The wind remained light to moderate from the southwest, so wind slab formation may be limited to immediate lee features.

Recent snowfall has been loading a touchy layer of feathery surface hoar crystals from late February that is found 30 to 60 cm deep. 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

  • Avoid freshly wind loaded terrain features.
  • Watch for avalanche hazard to increase throughout the day.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.

Problems

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.

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.