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Avalanche Forecast

Archived

Jan 30th, 2020–Jan 31st, 2020

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely.

Regions

Purcells.

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.

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

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

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.