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Avalanche Forecast

Archived

Feb 5th, 2013–Feb 6th, 2013

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

Fair - Due to variable snowpack conditions

Weather Forecast

Wednesday: Today the region sits under a weakening zonal flow maintaining moderate-strong ridgetop winds from the West. An upper disturbance embedded in the flow will bring snow amounts up to10 cm. Treeline temperatures steady -4 and freezing levels steady around 900 m. Thursday: Unsettled conditions continue, bringing light snow accumulations. Ridgetop winds will switch and blow from the SW. Treeline temperatures near -3 and freezing levels hovering around 1200 m, falling to valley bottom overnight.Friday: Outlook shows surface and upper ridge building, bringing dryer conditions and valley cloud. Treeline temperatures near -8 with freezing levels hovering around 900 m. Ridgetop winds blowing moderate from the NW.

Avalanche Summary

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

The old storm snow has settled into a dense slab that can be triggered by skiers or sledders and produce avalanches up to size 2.0. There has been a lot of wind transport and wind slab formation in the alpine. Forecast new snow and strong SW winds will build fresh wind slabs and add to the recent storm slab which sits on a spotty and variable weak interface 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 solar slopes due to a buried crust interface and 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.