Avalanche Forecast

Issued: Nov 22nd, 2012 9:12AM

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

swerner, Avalanche Canada

Purcells.

This bulletin is based on limited data. Local variations in conditions are likely to exist. Check out the Forecasters Blog for further details on interpreting early season bulletins.

Summary

Confidence

Poor - Due to limited field observations for the entire period

Weather Forecast

A Pacific frontal system will be dominating the coastal regions tonight. This system will move into the Interior regions on Friday bringing light â€“moderate snow accumulations.Â Through the weekend a NW flow will set up, bringing cooler, dryer conditions and partially sunny skies. Freezing levels remain in valley bottom through the period.Friday: Alpine -7, snow 5-10 cm, winds W 20km/hr.Saturday: Alpine -9, snow 5 cm, winds W 20km/hr switching NW.Sunday: Alpine -13, trace snow, winds NW 15km/hr.

Avalanche Summary

Recent avalanche control work in the Dogtooth Range produced Size 1.5-2.0 avalanches, running on the November 17th surface hoar layer. This layer is reactive to light loads, which means it could easily be triggered by a skier, or sled. If you and your friends have been outÂ riding in the backcountry, and have observations to share, please send an email to forecaster@avalanche.ca.

Snowpack Summary

Snowpack observations and information are very limited, and conditions across the region vary. In the alpine I suspect anywhere from 150-200 cm of snow. Wind slabs are reported to be widespread at treeline and in the alpine. The most suspect slopes that host touchy wind slabs are leeward (North-North East) and behind ridge crests and terrain features. An couple early season persistent layers also exist. The most reactive being a surface hoar layer that was buried on November 17th. This is buried down 25-50 cm. The early November crust also exists deeper in the snowpack and widespread in the alpine. At this point it seems to be unreactive in the Dogtooth Range, but may catch you by surprise in other parts of the region. Snow depths at treeline are roughly sitting around 50-100 cm in depth, and below treeline snow levels may still be below threshold.

Problems

Wind Slabs

Moderate SW winds have redistributed recent storm snow and has formed touchy wind slabs. Wind slabs exist on open leeward slopes and behind terrain features. Rider triggers are likely. Cracking, and whumphing are indicators of unstable snow.

Avoid cross loaded slopes at or above treeline.>Be cautious as you transition into wind affected terrain.>Be alert to conditions that change with elevation.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 5

Persistent Slabs

Two persistent layers exist through the region. A surface hoar layer buried 25-40 cm down, and an early Nov crust buried deeper below. These persistent slabs may be triggered by light loads, and propagate far across a slope.

Be aware of the potential for avalanches due to the presence of buried surface hoar.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 5

Valid until: Nov 23rd, 2012 2:00PM