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Avalanche Forecast

Archived

Feb 16th, 2019–Feb 17th, 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

Purcells.

Wind slabs are the primary concern at higher elevations and you shouldn't discount buried persistent weak layers at lower elevations. Don't be caught off guard with these variable snowpack conditions.

Confidence

High -

Weather Forecast

SATURDAY NIGHT: Mostly cloudy with isolated snowfall, trace in the north of the region and up to 8 cm in the south of the region, light to moderate northeast wind, alpine temperature -22 C.SUNDAY: Mostly clear skies, light to moderate northeast wind, alpine temperature -20 C.MONDAY: Mix of sun and cloud, light to moderate northwest wind, alpine temperature -18 C.TUESDAY: Cloudy with light snowfall, accumulation 1 to 3 cm, light to moderate west wind, alpine temperature -16 C.

Avalanche Summary

A persistent slab avalanche was triggered by a skier on Friday, releasing on the late-January surface hoar layer described in the Snowpack Summary. The avalanche was around 50 cm deep, on a south aspect, and in alpine terrain.

Snowpack Summary

Around 10 to 20 cm of recent snow has been blown around by strong, variable wind, creating touchy wind slabs in exposed areas. In the south and west of the region, recent storm amounts are closer to 30 to 40 cm. This new snow sits above wind-affected snow and/or sugary faceted grains. Beneath this lies two weak layers of surface hoar that were buried at the end of January and mid-January. These layers are around 30 to 70 cm deep. These layers are most prominent at treeline and below treeline elevations.The base of the snowpack is composed of weak and sugary faceted grains that overly a melt-freeze crust. This weak layer has produced large and destructive avalanches that are sporadic in nature and very difficult to predict. It is most likely to be triggered from areas where the snowpack is shallow and weak. Rocky alpine bowls, ridge crests, and rocky outcroppings are some examples of terrain features to be wary of. See the Forecaster Blog here for more information on this problem.

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.