Avalanche Forecast

Issued: Mar 21st, 2013 9:08AM

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

sylvia forest, Parks Canada

Glacier.

Incremental snow squalls and strong winds overnight are re-loading start zones and lee slopes. The sensitivity to skier triggering is quite variable, so good snowpack and terrain evaluation are required.

Summary

Weather Forecast

The air mass will become colder and more unsettled throughout the day, with convective flurries, cloud and moderate winds. A ridge will build for later Friday, and the weekend is looking dryer and sunnier.

Snowpack Summary

An intense frontal system passed through last night with strong winds. We suspect significant loading occurred in start zones overnight, but the bond of storm snow is not yet known. North aspects will be most loaded, but solar aspects may be more reactive due to a buried suncrust-surface hoar combo , where wide propagations can be expected.

Avalanche Summary

A small avalanche cycle occurred yesterday, mostly from steep start zones on Mt. MacDonald. Explosive testing yesterday produced a size 1 avalanche on a north aspect. Two days ago, skiers on Mt. Sifton cut a cornice to check the slope, and released a size 2.5-3 avalanche on a south aspect. See photo: Connaught

Confidence

Timing, track, or intensity of incoming weather system is uncertain on Friday

Problems

Storm Slabs

Multiple convective storms and frontal systems continue to add incremental load. The reactivity of the storm slabs is variable. We know that solar aspects are most reactive due to buried crusts, and north aspects received most load.

Carefully evaluate big terrain features by digging and testing on adjacent, safe slopes.Give cornices a wide berth when travelling on or below ridges.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 3

Wind Slabs

Isolated wind slabs in the alpine and near ridge crests have surprised a few skiers. These failures could break down to deeper instabilities. Cornices are very large and unsupported.

Be careful with wind loaded pocketsUse caution in lee areas in the alpine. Recent wind loading have created wind slabs.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

It will likely take a large trigger, like a cornice or another avalanche to trigger the Feb 12 and March 11 PWL's, now down 1-1.5m. The resulting avalanche would be very large and destructive if triggered.

Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

3 - 4

Valid until: Mar 22nd, 2013 8:00AM