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Avalanche Forecast

Archived

Mar 2nd, 2021–Mar 3rd, 2021

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

Regions

Kootenay Boundary.

We are uncertain how buried weak layers in the snowpack will respond to rising temperatures and strong sun. The considerable rating reflects the high likelihood for small loose wet avalanches in many areas and the potential for large persistent slab avalanches in specific areas.

Confidence

Moderate - We are confident the snowpack will rapidly lose strength with the arrival of the forecast weather. Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

Tuesday night: Clearing. Freezing level 1000 m. Moderate to strong southwesterly wind.

Wednesday: Sunny. Freezing level rising to 2000 m. Moderate southwest wind easing to light.

Thursday: Sunny. Freezing level 2300 m. Light to moderate southwest wind.

Friday: Sunny. Freezing level 2300 m. Moderate to strong southwest wind.

Avalanche Summary

On Monday, pinwheeling and small loose wet avalanches were observed out of steep, rocky solar exposed slopes in the afternoon. Over the weekend, there were a few natural and skier triggered wind slabs size 1.5, along with reports of wind slabs being stubborn to ski cuts. On Saturday, large explosive loads produced size 2-3 results at Kootenay Pass. In thin snowpack areas on solar aspects, a few of these large avalanches are suspected to have stepped down to the January layer described in the snowpack summary.

Snowpack Summary

At upper elevations, 20-40 cm of recent snow has seen significant wind effect, with reports of cross-loaded features and scouring on exposed windward aspects. Around treeline and below, the recent snow may sit over a layer of small surface hoar crystals in isolated areas.

A persistent layer buried 80-150 cm deep is composed of combinations of surface hoar, crusts and facets formed on the surface in late January. The problem seems to be most pronounced in thin snowpack areas on solar aspects. Recently, large explosive loads have been required to trigger an avalanche on this layer. But a rapid rise in temperature such as the one we are currently experiencing can also be a sufficient shock to these types of layers. If they start to become sensitive this week, we could see some large natural and human triggered avalanches.

Shallow snowpack areas in the east of the region may harbor a facetted basal snowpack as described in this MIN report. This structure is often a constant for thin snowpacks and can usually be managed with good travel habits of avoiding shallow rocky areas where the snowpack transitions from thick to thin. This is another layer that could be susceptible to shock from the warm temperatures this week and extra caution should be exercised in these types of snowpacks.

Terrain and Travel

  • Back off slopes as the surface becomes moist or wet with rising temperatures.
  • Extra caution for areas experiencing rapidly warming temperatures for the first time.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
  • If triggered loose wet avalanches may step down to deeper layers resulting in larger avalanches.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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.