Avalanche Forecast

Issued: Jan 15th, 2013 9:19AM

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

pgoddard, Avalanche Canada

Purcells.

Summary

Confidence

Fair - Freezing levels are uncertain

Weather Forecast

Wednesday-Friday: Strong north-westerly winds. Freezing level is at valley bottom, with alpine inversions possible (parcels of warm air which could bring alpine temperatures close to 0). Generally only trace amounts of snow.

Avalanche Summary

Several size 1-2 wind slabs were triggered naturally and by skiers on Tuesday morning. Wind slabs were also triggered remotely by a skier and a helicopter on Monday on steep lee slopes.

Snowpack Summary

Strong north-westerly winds have left hard and soft wind slabs in the lee of ridges and ribs at alpine and treeline elevations. Recent storm snow is settling over old snow surfaces including surface hoar (found especially at and below treeline in sheltered areas), a sun crust (on steep S to SW -facing slopes) and facets. The distribution of these weaknesses is patchy, but where they exist, it is still possible to trigger a large avalanche with the weight of a person or snowmobile. Watch out for rapid warming on alpine slopes over the next couple of days, which could weaken the slab above these interfaces. A strong mid-pack overlies a weak facet/crust layer near the base of the snowpack, which is now considered inactive.

Problems

Wind Slabs

Wind slabs may be found behind terrain breaks such as ridges and ribs. It may be possible for a wind slab to step down to a deeper instability.

Be cautious as you transition into wind affected terrain.>Be aware of the potential for wide propagations due to the presence of hard windslabs.>Give cornices a wide berth when travelling on or below ridges.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 5

Persistent Slabs

Persistent weaknesses are variable in their distribution, but can still be triggered by the weight of a person or snowmobile. Triggering persistent slabs will become more likely if the snowpack experiences rapid warming.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>Avoid convexities or areas with a thin or variable snowpack.>Choose the deepest and strongest snowpack areas on your run.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 5

Valid until: Jan 16th, 2013 2:00PM