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Avalanche Forecast

Archived

Feb 6th, 2013–Feb 7th, 2013

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

Regions

Cariboos.

Confidence

Good

Weather Forecast

Thursday: A weak upper trough moves through the region bringing unsettled conditions and light snow accumulations 5-10 cm. Ridgetop winds will light and blowing from the West. Treeline temperatures near -3 and freezing levels around 1100 m. Friday: Ridge of high pressure moves in with residual moisture and cloudy cover bringing only trace snow amounts. Ridgetop winds will switch and blow light from the NW. Treeline temperatures near -6 and freezing levels will hold stationary around 900 m.Saturday: Ridging continues accompanied by a fast moving, short lived weak disturbance. Trace of snow expected with ridgetop winds blowing moderate from the NW. Treeline temperature near -4 and freezing levels around 1300 m falling to valley bottom overnight.

Avalanche Summary

No new avalanches have been reported.Over the past couple of days a widespread natural avalanche cycle occurred up to size 2.5 mostly on NE-E aspects above 2000 m. A large natural size 3 slab avalanche was also reported from a large uneven south facing slope. the suspected failure plane being the buried crust down 40-80 cm. Several skier triggered avalanches up to size 2 were initiated from a variety of aspects and elevations ranging from 155-2200 m.

Snowpack Summary

Up to 25 cm of new snow sits on wind slabs and persistent weak interfaces. Wind slabs continue to develop and stiffen on lee slopes (N-SE) and behind terrain features like ridgelines and ribs. The old storm snow has settled into a dense slab that could be triggered by skiers or sledders and produce avalanches up to size 2.0. This slab sits on a spotty and variable weak interface comprising of crusts, surface hoar and facets which are buried  40-80 cm down. Professionals are finding the early January surface hoar layer to be well preserved in more locations below 2000 metres than had been suspected. Use extra caution on open slopes, cutblocks and convex rolls at and below treeline where buried surface hoar may be preserved.

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.

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.