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Avalanche Forecast

Archived

Feb 17th, 2015–Feb 18th, 2015

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

Regions

Purcells.

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Confidence

Good

Weather Forecast

The dominant ridge of high pressure should maintain a mix of sun and cloud on Wednesday, but looks like it will briefly flatten late in the day allowing more cloud and light precipitation to cross the province on Thursday. The freezing level on Wednesday is between 1500-1700 m, but an above freezing layer may develop higher in the alpine. On Thursday the freezing level dips to around 1500 m. On Friday we should bounce back to a mix of sun and cloud with slightly cooler temperatures. Winds are forecast to be light or moderate from the W-NW throughout the week.

Avalanche Summary

A couple natural slab avalanches up to size 2.5 were observed or reported on Monday. There were also a few explosive triggered slabs and cornice falls (some of which then triggered slabs) up to size 3. All activity was from very steep, high alpine terrain on a variety of aspects.

Snowpack Summary

Expect to find surface crusts on solar aspects and all aspects to at least 2000 m. At alpine elevations, thin new wind slabs or storm slabs may be found and cornices are large and weak. Underneath newly formed near-surface crusts, you may find moist snow. The late-Jan crust/surface hoar layer is 1-2 m deep in the west, and can be found within the upper metre of the snowpack further east. It is variably reactive and still the main concern in many areas. The mid-January surface hoar, deeper again, remains problematic in some areas. The mid-December and mid-November weak layers of crusts and facets can still be found near the bottom of the snowpack, particularly in shallower eastern parts of the Purcells.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.