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Avalanche Forecast

Archived

Dec 13th, 2020–Dec 14th, 2020

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

Regions

Purcells.

 Heightened avalanche conditions exist on wind loaded slopes and steep rocky terrain. There may also be an isolated weak layer 40 cm deep around Golden.

 

Confidence

Moderate - Recent weather patterns have resulted in a high degree of snowpack variability within the region.

Weather Forecast

A weak frontal system arrives on Tuesday.

SUNDAY NIGHT: A trace of snow overnight, moderate west wind, low temperatures around -8 C.

MONDAY: Cloudy with some light flurries, light southwest wind, high temperatures around -5 C.

TUESDAY: Scattered flurries with up to 5 cm of new snow, moderate southwest wind, high temperatures around -5 C.

WEDNESDAY: Another 5 cm of snow overnight then clearing in the afternoon, moderate west wind, high temperatures around -5 C.

Avalanche Summary

Avalanche control work produced a few small (size 1) storm slab and dry loose avalanches on Saturday.

A MIN report from the Clamshell near Golden reported a natural size 2.5 avalanche on Wednesday. This avalanche appears to have ran on a weak layer roughly 40 cm below the surface, which seems to be an isolated problem in this area.

Snowpack Summary

10-30 cm of soft snow overlies a rain crust found up to 2400 m in the south of the region and 1800 m in the north. In the north, the recent snow may sit over a weak layer of surface hoar or facets at elevations around treeline where this crust is not found. The recent snow may not be bonding well to these old surfaces. There have also been some reports of an isolated weak layer 40 cm below the surface around Golden.

The lower snowpack is characterized by a couple of crusts, the most notable is from a rain event in early November that is 50 to 100 cm deep. This crust is sitting near the base of the snowpack, surrounded by a weak layer of sugary facets. It is most likely to be reactive to human triggers or in a step-down from a smaller avalanche in shallow, rocky areas.

Terrain and Travel

  • Investigate the bond of the recent snow
  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

Problems

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.

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.