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Avalanche Forecast

Archived

Dec 21st, 2019–Dec 22nd, 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.

The Purcells have been getting blasted by this storm and with another round of fresh snow on Saturday night, avalanche hazard remains elevated. Continue to avoid avalanche terrain.

Confidence

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

SATURDAY NIGHT - Periods of snow, 10-20 cm / southwest wind, 20-40 km/h / alpine low temperature near -8

SUNDAY - Mainly cloudy with flurries, up to 5 cm / southwest wind, 10-20 km/h / alpine high temperature near -7

MONDAY - Mainly cloudy with scattered flurries, 5 cm / southwest wind, 10-20 km/h / alpine high temperature near -7

TUESDAY - Cloudy with sunny periods / southwest wind, 10-20 km/h / alpine high temperature near -10

Avalanche Summary

With more snow overnight on Saturday, avalanche activity is expected to continue to be widespread on Sunday.

Avalanche activity was widespread on Saturday with reports of natural, human and explosives triggered avalanches up to size 3.

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

Snowpack Summary

The storm delivers a final punch to the Purcells with another 10-20 cm overnight Saturday, and up to 5 cm during the day on Sunday. The region has received a whopping 60-115 cm of new snow since Thursday night. Storm slabs are widespread and are expected to continue to be reactive on Sunday.

Anywhere from 70-160 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 90-180 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.