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Avalanche Forecast

Archived

Feb 5th, 2022–Feb 6th, 2022

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

Regions

Kootenay Boundary.

Wind slabs, loose avalanches, and weak cornices are all expected Sunday.

There is a lot of uncertainty about how buried weak layers are going to react to the sun and warming. Use a conservative approach to terrain selection and watch for signs of instability.

Confidence

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather. Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

A ridge of high pressure brings dry and sunny conditions for Sunday with a layer of warm air expected to reach the alpine and a temperature inversion in the valleys. 

Saturday Night: Mainly clear, light to moderate NW wind, treeline temperature around -5 °C. 

Sunday: Mainly sunny with some valley cloud, light to moderate W wind, freezing level reaching over 2000 m in the afternoon with a temperature inversion. 

Monday: A mix of sun and cloud, moderate W wind, warm air aloft breaking down in the early morning, afternoon freezing level reaching around 1500 m.

Tuesday: Mainly sunny, light to moderate W wind, freezing level reaching around 1500 m.

Avalanche Summary

An early report from Saturday includes two natural size 1 storm slabs failing overnight on southerly aspects between 2100 m and 1700 m. 

On Friday, explosive-triggered wind slabs up to size 1.5 were reported which were 10-30 cm thick. Just north of the region, a natural slab avalanche was reported on a NE aspect at 1850 m failing down 15 cm. On Thursday, ski cutting triggered size 1-2 wind slabs mainly on NE aspects above 2100 m elevation.  

Snowpack Summary

Up to 50 cm of settling snow now overlies the January 30 interface which consists of a melt-freeze crust at lower elevations and on solar aspects extending into the alpine, widespread surface hoar in sheltered areas at and below treeline, and small facets in some areas. Prior to the weekend warming, the surface storm snow was cold and mainly unconsolidated, and had not formed a slab in most places except for where it was wind loaded. With warming and sun this weekend, rapid settlement is possible and this may result in the formation of a more widespread reactive slab over the weak interface. 

Periods of strong wind over the past week has formed reactive wind slabs in exposed terrain at higher elevations and ongoing wind on Friday and Saturday, mainly from the southwest through northwest, has likely continued to develop wind slabs. 

A crust/surface hoar interface from mid-January is now down around 40-70 cm. It has been dormant recently but there is concern that this layer may also wake up with some warming and sun. 

The early December crust/facet persistent weak layer is buried down 100-200 cm. It had been responsible for significant avalanche activity in this region during the first half of January but is now considered dormant. See this forecaster blog on how to manage this layer as it may come into play again later this season. 

Check out this great video from Whitewater from Thursday for a detailed look at the snowpack in that part of the region. 

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 weak layers.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
  • The more the snowpack warms-up and weakens, the more conservative you`ll want to be with your terrain selection.
  • Cornices become weak with daytime heating or solar exposure.

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.

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.