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Avalanche Forecast

Archived

Feb 27th, 2017–Feb 28th, 2017

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

Regions

Cariboos.

Danger will increase throughout the week with new snow and strong winds in the forecast. Triggering a deep persistent slab is the primary concern and warrants a cautious approach to terrain.

Confidence

Moderate - Forecast snowfall amounts are uncertain on Wednesday

Weather Forecast

TUESDAY: Cloudy with flurries starting in the afternoon, moderate southwest winds with strong gusts, alpine temperatures around -15 C.WEDNESDAY: Continued flurries with 5-10 cm of new snow, moderate southwest winds with strong gusts, alpine temperatures around -10 C.THURSDAY: Another 10 cm of new snow, strong southwest winds,  alpine temperatures around -8 C.

Avalanche Summary

On the weekend several natural wind slabs in the size 1-2 range were reported in steep alpine terrain. Many parts of the region have a similar snowpack structure to Clemina Creek, where two size 2 snowmobile triggered persistent slab avalanches were reported on Saturday (see MIN report here). Triggering a large deep persistent slab avalanche is a low probability - high consequence scenario that warrants an extra cautious approach to terrain. See here for a list of recent near misses in the Cariboos and North Rockies.

Snowpack Summary

New wind slabs have formed on a variety of aspects in alpine terrain thanks to shifting wind directions. Light flurries over the past week have delivered a total of 15-30 cm of low density snow, while sun crusts have formed on steep south slopes. The recent snow has buried the mid-February interface, which is composed of a thick rain crust up to about 1700 m, sun crusts on steep solar aspects, and spotty surface hoar on shaded aspects. Some lingering surface hoar layers from January are down about a metre and the weak mid-December facets are down about 1.5 metres. These deep persistent weaknesses still have the potential to react to human triggers.

Problems

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.

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.