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Avalanche Forecast

Archived

Feb 23rd, 2012–Feb 24th, 2012

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
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

South Rockies.

Confidence

Fair - Forecast snowfall amounts are uncertain on Saturday

Weather Forecast

A low pressure system is moving inland from the coast on Friday. This system is forecast to bring snow and moderate southwest wind to the Kootenay Boundary by afternoon and to the South Rockies region by the early evening. Snowfall amounts are forecast to be about 5 cm for the South Rockies on Friday. Another 10-15 cm for the South Rockies and 15-20 cm in the Lizard Range are expected overnight and during the day on Saturday. Sunday is forecast to be a mixed bag of convective flurries and some sunny periods. The freezing level is expected to rise to about 700 metres on Friday, drop back to valley bottom overnight and then rise to near 1200 metres on Saturday.

Avalanche Summary

We have reports of numerous avalanches up to size 2.5 with crowns about 40-50 cm on N-NE aspects in the Corbin area of the Flathead.

Snowpack Summary

Gusty wind has transported snow into windslabs at all elevations. In southern and western parts of the region, 40-50 cm of recent snow sits of a highly reactive weak layer of crusts, surface hoar and facets. At 1950 metres elevation we have some snow pack test results that show that the 40 cm slab of snow above the February 8th weak layer is sliding with easy to moderate forces applied and it is propagating widely with either sudden planar or sudden collapse characteristics. The slab is reported to be less consolidated on northerly aspects than it is on southerly aspects. In areas further north, less snow has fallen on this interface--in the northern Elk Valley for instance, only around 15-20 cm lies above this interface. In lower snow areas, avalanche activity will likely lag behind higher snow areas, except for areas which have seen significant wind transport. In general, the mid-pack is quite strong in most locations. However, lingering concern remains for basal facets, particularly in shallower snowpack areas with steep, rocky start zones.

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.