Avalanche Forecast

Issued: Feb 17th, 2015 7:43AM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is low. Known problems include Wind Slabs, Persistent Slabs and Loose Wet.

Peter, Avalanche Canada

Purcells.

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Summary

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

Fresh wind slabs may be lurking behind ridges and terrain features. Cornices are also large and weak and could collapse.

Use ridges or ribs to avoid pockets of wind loaded snow.>Give cornices a wide berth when travelling on or below ridges.>

Aspects: North, North East, East, South East, South.

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 3

Persistent Slabs

Persistent slabs are most likely to be triggered from thin snowpack areas, or with large triggers like cornice fall or an avalanche stepping down.

Avoid common trigger points like convexities or areas with a thin or variable snowpack.>Do not travel on slopes that are exposed to cornices overhead.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Loose Wet

Expect loose wet sluffs on steep sun-exposed slopes. These could trigger persistent weaknesses if they gain significant mass.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Feb 18th, 2015 2:00PM