Avalanche Forecast

Issued: Jan 30th, 2020 4:00PM

The alpine rating is high, the treeline rating is high, and the below treeline rating is considerable. Known problems include Storm Slabs, Deep Persistent Slabs and Loose Wet.

Avalanche Canada cgarritty, Avalanche Canada

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Avalanche danger is expected to become HIGH before the end of the day as heavy precipitation, strong winds, and rising temperatures make their way into the region. Be aware of conditions changing over the day, especially in overhead terrain.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Thursday night: Becoming cloudy with increasing flurries bringing 5-15 cm of new snow. Light to moderate southwest winds, becoming strong at ridgetop.

Friday: Cloudy with continuing snowfall bringing 10-25 cm of new snow, transitioning to rain below about 1900 metres. Strong southwest winds. Alpine high temperatures reaching 0 to +1 as freezing levels climb to 2000- to 2300 metres over the day.

Saturday: Continuing snowfall bringing 10-20 cm of new snow to the alpine, rain below about 1700-1800 metres. Moderate souhwest winds, becoming strong at ridgetop. Alpine temperatures around 0 with freezing levels beginning to fall from 2000 metres in the afternoon.

Sunday: Mainly sunny. Light southwest winds. Alpine high temperatures around -9.

Avalanche Summary

On Sunday there were three deep persistent slab avalanches reported in the region. Two were triggered by explosives, but one that occurred near Golden was remotely triggered by humans. This activity outlines the fact that this layer remains a problem in the region. Large alpine features, especially rocky, thin snowpack areas are the most likely places to trigger this layer.

Over the past week there have been a few reports everyday of natural, human and explosives triggered storm slab and wind slab avalanches up to size 3, but mostly around size 1-2. These have occurred on all aspects, mainly at treeline and alpine elevations. The peak of this activity occurred on Saturday and has been tapering since. Wind loaded areas at treeline and in the alpine remain the most likely places to trigger an avalanche.

Looking forward, heavy precipitation, strong winds, and rising temperatures will promote increasing natural avalanche activity on Friday. During this time, deep persistent slab releases such as those mentioned above may result from avalanche activity in surface snow layers.

Snowpack Summary

A variable 15-40 cm of new snow is expected to fall at the highest elevations of the region by end of day on Friday. The new snow will cover wind affected recent snow at alpine and upper treeline while rain saturates the surface below about 1900 metres.

A weak layer of surface hoar can currently be found about 70 cm deep around Golden and Kimberley, 30 cm deep around Invermere, and 100 cm deep along Kootenay Lake.

As usual for the Purcells, the base of the snowpack contains basal facets and it remains possible to trigger these deep weak layers in shallow rocky start zones or from a heavy trigger such as a cornice fall or explosives.

New snow, rain, and warming will collectively add considerable strain to these weak layers. Their potential to fail naturally and produce large, destructive avalanches will be significantly increased during the storm.

Terrain and Travel

  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.

Problems

Storm Slabs

An icon showing Storm Slabs

Rapid loading of new snow during Friday's storm will build new storm slabs at higher elevations. Forecast strong winds and warm temperatures will speed slab formation as new snow accumulates. Danger will be greatest in western and central parts of the region

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Very Likely

Expected Size

1 - 2

Deep Persistent Slabs

An icon showing Deep Persistent Slabs

Triggering deep persistent slab avalanches is a relatively low likelihood but high consequence problem that is most likely in shallow, rocky start zones. Smaller wind slab avalanches could step down to this deeper layer, resulting in a very large avalanche.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 3

Loose Wet

An icon showing Loose Wet

Wet loose avalanches will be in increasing problem on Friday at lower elevations that see rain instead of snow accumulating. This problem will affect increasingly high elevations over the day.

Aspects: All aspects.

Elevations: Below Treeline.

Likelihood

Very Likely

Expected Size

1 - 1.5

Valid until: Jan 31st, 2020 5:00PM