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Avalanche Forecast

Archived

Feb 20th, 2019–Feb 21st, 2019

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.

Though avalanche activity has slowed down, it is worth keeping in mind that the potential still exists for humans to trigger persistent slab avalanches. While these avalanches are becoming less likely, the consequences remain high.

Confidence

High -

Weather Forecast

WEDNESDAY NIGHT - Cloudy with clear periods and isolated flurries / northeast winds 10-20 km/h / alpine low temperature near -12THURSDAY - A mix of sun and cloud with isolated flurries / northwest winds 10-20 km/h / alpine high temperature near -10FRIDAY - Mainly cloudy with flurries, 5-10 cm / southwest winds 15-35 km/h / alpine high temperature near -10SATURDAY - A mix of sun and cloud with isolated flurries / northwest winds, 10-15 km/h / alpine high temperature near -10

Avalanche Summary

On Tuesday, a notable avalanche report was of a size 3 persistent slab avalanche that occurred on an east aspect between 1800-2100 m. This avalanche was triggered by explosives and it reportedly failed on the persistent weak layer that was buried on February 7th. This layer is discussed further in the Snowpack Summary below.Human triggered avalanches have been reported everyday for over a week. Although most avalanches have been small (size 1-1.5), some have shown impressive propagation. Check some of the recent MIN reports for examples (here and here).

Snowpack Summary

Depending on location, the snow surface consists of a mix of 20-30 cm of low density snow or wind slabs, and sun crust on south facing slopes.  This snow sits on a weak layer of surface hoar (feathery crystals) and a crust that was buried on February 7th. This layer has been reactive, and has produced avalanches as large as size 3. Two other surface hoar layers are buried 50 to 80 cm deep the snowpack (referred to as the February 1st and mid-January layers). Although they have not been reactive recently, they are still being monitored by professionals. These layers are most prevalent below treeline on shady aspects. The lower snowpack is considered generally strong.

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.