Avalanche Forecast

Issued: Feb 21st, 2013 9:08AM

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

jlammers, Avalanche Canada

Purcells.

Local snowpack and weather variations exist throughout the region. Be aware of conditions that are specific to your area and make observations continuously as you travel.

Summary

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Friday: Moderate to locally heavy snowfall / Strong to extreme southwest winds / Freezing level at 1200mSaturday: Light snowfall / Moderate northwest winds / Freezing level at surfaceSunday: trace amounts of snow / Light southwest winds / Freezing level at 1000m

Avalanche Summary

A size 1.5 skier accidental slab avalanche was observed at treeline on Wednesday. The slide, which occurred on a northeast aspect, had a crown of 25cm and is reported to have released on the February 15th surface hoar.Two size 1.5 slab avalanches were triggered on Wenesday by natural cornice fall on a north aspect at treeline. The crown was between 40 and 50cm deep and is reported to have failed on the February 12th surface hoar.Increased avalanche activity is expected with weather forecast for Friday.

Snowpack Summary

Dribs and drabs of recent low density snow add to a slab which overlies reactive layers of surface hoar that were buried on February 12th and February 15th. These layers currently sit between 15 and 60cm below the surface. The slab may also be reactive on southerly aspects where buried sun crusts exist. Loading from new snow and wind on Friday may cause another cycle of natural activity, or an increased sensitivity to human triggers. There are older weak layers that are now buried down around 70-80 cms and also at about 110 cms. These layers have been less likely to trigger by skiers, but they may still be sensitive to large loads like avalanches in motion or cornice fall.

Problems

Storm Slabs

Friday's forecast snowfall amounts are highly variable throughout the region. Where higher accumulations exist, large storm slab avalanches are likely, especially in wind-affected areas.

Be cautious as you transition into wind affected terrain.>Avoid all avalanche terrain during periods of heavy loading from new snow and wind.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

Loading from new snow and wind will likely add reactivity to persistent buried surface hoar layers. In higher snowfall areas, resulting avalanches may be surprisingly large and destructive.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>Choose well supported terrain without convexities.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2 - 5

Valid until: Feb 22nd, 2013 2:00PM