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Avalanche Forecast

Archived

Feb 13th, 2013–Feb 14th, 2013

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Purcells.

Confidence

Fair - Timing or intensity of solar radiation is uncertain on Friday

Weather Forecast

Overnight and Thursday: Mostly clear with cold temperatures overnight and nil precipitation. Strong Westerly winds are expected to decrease to moderate Northwesterly by morning. Freezing levels down to the valley bottom overnight, and then rising up to about 1300 metres during the day.Friday: Moderate to strong  Northwest winds with Alpine temperatures around -5.0 and freezing levels rising to around 1600 metres. Expect broken skies and periods of strong solar radiation.Saturday: The ridge of high pressure is expected to flatten and move off to the East. An upper trough is expected to bring flurries and light snow falls to the region by the afternoon.

Avalanche Summary

There was one report of a natural size 2.0 wind slab release on a North aspect in the alpine from a shallow snowpack area.

Snowpack Summary

The snow surface consists of new wind slab in exposed alpine terrain, a sun crust on solar aspects, and surface hoar and/or facets on shady slopes - all getting dusted by new snow on Tuesday. The recent storm slab continues to settle over old interfaces comprising of surface hoar, crusts and facets down 30-50 cm (Jan 23 interface). One recent snowpack test from the Dogtooth Range on a west aspect in the alpine gave moderate "pops" results and showed potential for propagation on a this facet/crust layer. Continued freezing temperatures overnight have helped to strengthen the snowpack at lower elevations.The mid-pack is generally well settled and the average snowpack depth at treeline elevations is near 130. Cornices have grown and may threaten slopes below.

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.