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Avalanche Forecast

Archived

Feb 16th, 2019–Feb 17th, 2019

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

Regions

Kootenay Boundary.

A cautious approach to backcountry travel is recommended as we come out of a period of active avalanche activity.

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

SATURDAY NIGHT: Light flurries of low density snow with accumulations of 2-8 cm, light northeast wind, alpine temperatures drop to -15 C.SUNDAY: More spotty flurries of low density snow into the afternoon, accumulations up to 5 cm, light north wind, alpine temperatures around -15 C.MONDAY: Mix of sun and cloud, moderate northwest wind, alpine high temperatures around -15 C.TUESDAY: Cloudy with isolated flurries and trace accumulations, wind, alpine high temperatures around -15 C.

Avalanche Summary

Avalanche activity began to quite down on Saturday after four strait days of widespread storm slab and wind slab activity.On Friday, skiers triggered numerous size 1-1.5 storm slab avalanches and loose dry avalanches on all aspects in steep terrain (see this MIN report for an example here). On Thursday, strong wind formed fresh wind slabs that produced several size 1-2 natural avalanches. The wind slabs were very reactive to human triggering on all aspects. Two large (size 2) skier-triggered slab avalanches were reported at treeline elevations with crowns up to 80 cm thick.

Snowpack Summary

A total of 30 to 50 cm of snow has fallen over the past few days. The snow remains low density in some sheltered areas, but was dramatically affected by a wind event on Thursday that left hard wind slabs in exposed terrain. The new sits on a variety of old surfaces that include a sun crust on southerly aspects, variable wind-affected snow, and weak feathery surface hoar crystals at and below treeline. The snowpack hosts two buried surface hoar layers. The February 1st surface hoar is down 40 to 60 cm and has been recently reactive to human triggers. The mid-January surface hoar is 60 to 100 cm below the surface. This deeper layer of surface hoar is most prevalent below treeline on shady aspects, but it does not seem to be a widespread problem in the region. Below that, the snowpack is well settled.

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.