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Avalanche Forecast

Archived

Dec 20th, 2019–Dec 21st, 2019

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
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

Purcells.

It's a great weekend to hit the ski hill! Widespread avalanche activity is expected today. Avoid avalanche terrain.

Confidence

High -

Weather Forecast

FRIDAY NIGHT - Periods of snow, 15-25 cm / southwest wind, 30-60 km/h / alpine low temperature near -3 / freezing level 1500 m

SATURDAY - Periods of snow, 15-30 cm / southwest wind, 40-80 km/h / alpine high temperature near -3 / freezing level 1500 m

SUNDAY - Cloudy with sunny periods and isolated flurries, up to 5 cm / southwest wind, 10-20 km/h / alpine high temperature near -5 / freezing level 1000 m

MONDAY - A mix of sun and cloud / southwest wind, 10-20 km/h / alpine high temperature near -7

Avalanche Summary

Significant snowfall amounts, warm temperatures and strong to extreme winds will mean that a natural avalanche cycle is expected on Saturday.

On Friday there were reports of numerous natural, human and explosives triggered avalanches. 

Snowpack Summary

The storm rages on in the Purcells with 15-25 overnight on Friday and another 15-30 cm expected during the day on Saturday. By the end of the day on Saturday, this will make for a total of 50-95 cm of snow in 48 hours. Storm slabs are expected to be widespread and very reactive.

Anywhere from 70-150 cm of recent snow may sit on a weak layer of surface hoar in sheltered areas at treeline. A second layer of surface hoar primarily found in the in north of the region is found 90-170 cm below the surface in sheltered areas at treeline. There are a variety of crusts buried in the mid to lower snowpack. These crusts have mostly broken down. The base of the snowpack generally consists of facets and depth hoar.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Avoid the runout zones of avalanche paths. Avalanches could run full path.

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.

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.