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Avalanche Forecast

Archived

Feb 18th, 2019–Feb 19th, 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

MONDAY NIGHT: Cloudy with clear periods, moderate northwest wind, alpine temperatures drop to -15 C.TUESDAY: Cloudy with isolated flurries and trace accumulations, moderate northwest wind, alpine high temperatures around -10 C.WEDNESDAY: Cloudy with isolated flurries, light to moderate northeast wind, alpine high temperatures around -8 C.THURSDAY: Mostly cloudy, light north wind, alpine high temperatures around -10 C.

Avalanche Summary

Numerous skier triggered avalanches have been reported every day since Tuesday. Although most avalanches have been small (size 1-1.5), they have shown impressive propagation. Check some of the recent MIN reports for examples (here and here). On Sunday, freshly wind loaded features were very reactive to skier triggering, with a size 1.5 avalanches reported on convex features a variety of aspects. A few size 1.5 persistent slab avalanche were remotely triggered, primarily on south and east aspects at treeline. There were also several reports of whumpfing, indicating touchy persistent weak layers in the snowpack.

Snowpack Summary

Surface snow consists of a mix of low density snow and wind affected surfaces. 20 to 40 cm of snow from the past week 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.