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Avalanche Forecast

Archived

Feb 19th, 2019–Feb 20th, 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.

Human triggered avalanches remain possible at all elevations. A cautious approach to backcountry travel is recommended.

Confidence

High -

Weather Forecast

TUESDAY NIGHT - Mainly cloudy with scattered flurries / northwest winds 10-20 km/h / alpine low temperature near -13WEDNESDAY - A mix of sun and cloud / northeast winds 10-20 km/h / alpine high temperature near -11THURSDAY - A mix of sun and cloud / southwest winds 10-20 km/h / alpine high temperature near -13FRIDAY - Mainly cloudy with flurries / southwest winds, 15-35 km/h / alpine high temperature near -12

Avalanche Summary

On Monday, there were reports of several natural and human triggered avalanches to size 2.5 on both north and south aspects at alpine and treeline elevations.On Sunday, there were reports of both natural and human triggered avalanches to size 2. Most of these were either storm slabs or wind slabs, but a few of them were persistent slabs that failed on a persistent weak layer that was buried in mid January. There is a great MIN report of a human triggered persistent slab avalanche on Sunday in the Hellroaring Creek area here.Small wind slab and storm slab avalanches were triggered in alpine terrain on Saturday.On Friday, a persistent slab avalanche was triggered by a skier, 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 20 to 30 cm of recent snow has been blown around by recent strong, variable wind, creating touchy wind slabs in exposed areas. In the south and west of the region, recent snowfall amounts are closer to 40 to 50 cm. This new snow sits above wind-affected snow and/or sugary faceted snow.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.