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Avalanche Forecast

Archived

Feb 20th, 2015–Feb 21st, 2015

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

Regions

Cariboos.

A good dusting of fresh snow should improve the snow quality but watch for deep and touchy pockets of wind slab in wind exposed terrain.

Confidence

Good

Weather Forecast

The ridge of high pressure rebuilds and should result in clearing skies in most parts of the Province. However, there is a weak cold front sliding in from the east that could bring cloud and light snow to parts of the Southern Interior (particularly the east side of Purcells). By Sunday all regions should be enjoying sunny skies. The freezing level on Saturday is 500-1000 m and it bumps up a couple hundred metres each day. Ridge winds are light gusting to moderate from the NW to NE.

Avalanche Summary

Avalanche activity has gradually tapered off throughout the week. On Thursday there were a couple reports of natural cornice falls, but these did not trigger slabs. There was also a report of a size 1 (20 cm deep) skier controlled wind slab from an East facing slope. Wind slabs could build and remain sensitive to rider triggering throughout the weekend.

Snowpack Summary

A dusting of new snow (~10 cm) covers the previous variable snow surface of surface hoar, crusts, dry facetted snow, or wind affected snow depending on aspect and elevation. The "Valentine's Day" crust is just below the surface and is now strong and thick in most places. New wind slabs may have formed in lee terrain from recent W-NW winds, and cornices remain large and weak. The late-Jan crust/surface hoar layer (up to 100 cm deep) and the mid-January surface hoar (80-120 cm deep) continue to give variable results in snowpack tests. Chances of triggering these weaknesses have decreased, but triggering may be possible from thin or rocky snowpack areas; or perhaps with a cornice fall, or an avalanche stepping down, especially on sun drenched slopes.

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.