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Avalanche Forecast

Archived

Dec 16th, 2015–Dec 17th, 2015

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

Regions

Purcells.

It sounds like good riding conditions out there but large human triggered avalanches are still possible. Start with small test slopes and build up slowly to bigger features.

Weather Forecast

THURSDAY: no new snow is expected, mainly light south winds, remaining cool, -10C at 1500m. FRIDAY: Light snow fall, up to 10cm, with the greatest accumulations in the south of the region, moderate westerly winds, still cool. SATURDAY: light snowfall, up to 5cm, again mainly in the south, light southerly winds, cool.

Avalanche Summary

Avalanche activity appears to have tapered off since the weekend.  Avalanche professionals in the field are reporting sluffing in steep terrain in response to skier traffic (aka good riding conditions) and some lingering reactive pockets of wind slab in steep lee features. No new avalanches have been reported on the layer of buried surface hoar since last week, however, people have been experiencing wumphing and other signs of instability from safe terrain as they travel between 1400 and 1800m.

Snowpack Summary

It sounds like good riding conditions out there with mainly low density snow on the surface. There is some localized wind effect in the new snow at ridgeline. About 15 to 40cm of snow sits above a crust that extends up to 1800m. The early December persistent weak layer can now be found down 30-80cm.  This layer can be found as an old sun crust on solar aspects in the alpine, or as large grained surface hoar and small facets in isolated pockets bellow treeline.  The surface hoar is mainly a problem between 1400m and 1800m, although it may extend higher in the south of Invermere. Snow pit tests on this interface have been widely variable; producing a mixture of sudden and resistant failures or no results. The mid and lower portions of the snowpack are thought to be mainly well settled.

Problems

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.

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.