Avalanche Forecast

Issued: Feb 17th, 2015 7:41AM

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

Peter, Avalanche Canada

South Columbia.

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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 1500-2000 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

Explosive control work on Monday produced a few size 2-3 slab avalanches. Most of these were from steep alpine slopes and the majority were on southerly aspects. There were also a couple reports of natural and explosive triggered cornice falls, some of which triggered slabs up to size 2 (one stepped down to the November crust). This recent activity suggests that conditions have improved, but large loads (like a cornice fall) could still trigger deeper persistent weaknesses, primarily in alpine terrain.

Snowpack Summary

The snow surface is a mix of surface hoar, crusts, low density 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. At alpine elevations, new wind slabs may have formed from NW winds, and cornices are 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

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

Be cautious as you transition into wind affected terrain.>Avoid steep slopes below cornices.>

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 3

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

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.>Avoid steep slopes below cornices.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely

Expected Size

3 - 6

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