Avalanche Forecast

Archived

Feb 17th, 2019–Feb 18th, 2019

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.

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.

Triggering slab avalanches remains possible at all elevations and aspects. Carefully watch for signs of instability such as whumpfs and cracking.

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

SUNDAY NIGHT: Clearing skies overnight, moderate northwest wind, alpine temperatures drop to -18 C.MONDAY: Mix of sun and cloud, moderate northwest wind, alpine high temperatures around -13 C.TUESDAY: Cloudy with isolated flurries and trace accumulations, moderate to strong northwest wind, alpine high temperatures around -13 C.WEDNESDAY: Cloudy with isolated flurries, light northeast wind, alpine high temperatures around -10 C.

Avalanche Summary

Numerous skier triggered slab avalanches have been reported daily since Tuesday. Although most avalanches have been small (size 1-1.5), they have shown impressive propagation. See these examples from recent MIN reports here and here. Preliminary reports from Sunday indicate freshly wind loaded features were reactive to skier triggering, with a few size 1.5 avalanches reported on a variety of aspects. A persistent slab avalanche was remotely triggered slab on a east aspect at 1850 m. It failed on a 30 cm deep surface hoar layer. On Saturday, a few small (size 1-1.5) slab avalanches were triggered by skiers on convex terrain, especially on south aspects. On Thursday, strong wind formed fresh wind slabs that produced several size 1-2 natural avalanches. The wind slabs were also very reactive to human triggering and produced two large (size 2) skier-triggered slab avalanches (with 80 cm thick crowns).

Snowpack Summary

Surface snow consists of a mix of low density snow and hard wind affected surfaces. 20 to 40 cm of snow from the past few days is gradually settling, and in some areas has shown signs of becoming reactive above above a surface hoar and crust layer that was buried on February 7th. This layer is suspect at all elevations, particularly on wind loaded slopes and on steep south-facing terrain.Two other surface hoar layers are buried 50 to 80 cm deep the snowpack (referred to as the February 1st and mid-January layers). Although they have not been reactive recently, they are still being monitored by professionals. These layers are most prevalent below treeline on shady aspects. The lower snowpack is well settled.

Problems

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.

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.