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Avalanche Forecast

Archived

Mar 12th, 2018–Mar 13th, 2018

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

Regions

Purcells.

Avalanche danger will increase on sunny slopes where wet loose avalanches are very likely. Concern is increasing for persistent slabs and cornices.See the Forecaster's Blog for more: http://www.avalanche.ca/blogs/2018-03-09-first-big-warm-up

Confidence

Moderate - Timing or intensity of solar radiation is uncertain on Tuesday

Weather Forecast

Sunny and warm until light precipitation arrives on Wednesday. TUESDAY: Mainly sunny with some thin cloud. Light southerly winds. Freezing level to 2500 metres with alpine high temperatures of +3.WEDNESDAY: Cloudy with rain or isolated wet flurries (2-5 cm possible). Light to moderate south west winds. Freezing level falling to 1700 metres late in the day, with alpine high temperatures of +1.THURSDAY: Scattered wet flurries (2-5cm). Light southerly winds. Freezing level rising to 2000 metres with alpine high temperatures around 0 degrees.

Avalanche Summary

On Sunday we received reports of a skier caught in a size 2.5 avalanche in the north of the region. The slab was 20-50 cm thick and started on a steep north east aspect immediately below ridge crest at 2300m. See the MIN post for more details. Numerous wet loose avalanches were observed in the region to size 2.5 over the past three days, on sunny aspects. Avalanche activity is expected to increase as we move into a period of intense sun and prolonged warming. Predictable loose wet avalanches from steep, sunny terrain should be easy to manage. The trickier beast will be when warmth penetrates into the snowpack to tickle deeper persistent weak layers. The next few days will be a time to avoid exposure to large sun-exposed features and keep well away from corniced slopes.

Snowpack Summary

Around 10-15 cm of new snow from last week sits on sun crusts on solar aspects. A couple of layers buried in mid-late February (down around 40-100 cm) are variably reactive, but both have the potential to create surprisingly large avalanches if triggered. Initially, these interfaces were most reactive on solar aspects, where they present as buried sun crusts. However, persistent slabs have been triggered on shady aspects too, where surface hoar and/or facets exist (see the Avalanche Summary above for more information).Deeper persistent weak layers from January and December are generally considered dormant, but could wake up with forecast warming, a surface avalanche stepping down, cornice fall, or a human trigger in a shallow or variable-depth snowpack area. These layers consist of sun crust, surface hoar and/or facets. Facets also linger at the base of the snowpack.

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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.