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Avalanche Forecast

Archived

Feb 15th, 2019–Feb 16th, 2019

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

Regions

Kootenay Boundary.

Human-triggered avalanches are likely this weekend as the new snow continues to be very reactive. Stick to simple well-supported terrain.

Confidence

Moderate - Forecast snowfall amounts are uncertain on Saturday

Weather Forecast

A low pressure system will linger over the southeast corner of the province until Sunday morning, which will bring steady low density snowfall to the region. Exact amounts are uncertain.FRIDAY NIGHT: Light flurries with 5-10 cm of low density snow, moderate west wind, alpine temperatures drop to -10 C.SATURDAY: Light flurries continue with another 5-10 cm of low density snow, moderate west wind, alpine high temperatures around -8 C.SUNDAY: Scattered flurries in the morning then clearing in the afternoon, light wind, alpine high temperatures around -12 C.MONDAY: Mix of sun and cloud, light north wind, alpine high temperatures around -14 C.

Avalanche Summary

Slab avalanche activity has been reported daily since Tuesday's storm, and is expected to continue into the weekend with the ongoing snowfall.Preliminary reports from Friday, include numerous large (size 2-2.5) explosive triggered storm slabs on south aspects.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. Numerous smaller (size 1) skier-triggered wind slabs were also reported, including some triggered from a distance (remotely).

Snowpack Summary

A total of 30 to 50 cm of fresh snow has fallen over the past few days and has been very reactive to human triggering. A strong wind event on Thursday formed fresh wind slabs in exposed terrain (see this MIN report), while low density snow may still be found in sheltered areas. 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.