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Avalanche Forecast

Archived

Nov 22nd, 2012–Nov 23rd, 2012

Alpine
Below Threshold.
Treeline
Below Threshold.
Below Treeline
Below Threshold.
Alpine
Below Threshold.
Treeline
Below Threshold.
Below Treeline
Below Threshold.
Alpine
Below Threshold.
Treeline
Below Threshold.
Below Treeline
Below Threshold.

Regions

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.

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 –moderate snow accumulations.  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 out  riding in the backcountry, and have observations to share, please send an email to [email protected].

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

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.