Avalanche Forecast

Issued: Feb 18th, 2019 4:43PM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Wind Slabs and Persistent Slabs.

kdevine, Avalanche Canada

Purcells.

Wind slabs at upper elevations, and persistent slabs at lower elevations remain a concern as they can be triggered by humans. A cautious approach to backcountry travel is recommended.

Summary

Confidence

High -

Weather Forecast

MONDAY NIGHT - Clear periods / west winds 10-20 km/h / alpine low temperature near -17TUESDAY - Mainly cloudy with flurries / southwest winds 10-25 km/h / alpine high temperature near -11WEDNESDAY - A mix of sun and cloud with isolated flurries / northeast winds 10-20 km/h / alpine high temperature near -9THURSDAY - A mix of sun and cloud / east winds, 10-15 km/h / alpine high temperature near -12

Avalanche Summary

Preliminary reports from Monday indicate continued avalanche activity with both human triggered wind slab avalanches and natural persistent slab avalanches to size 2 being reported.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

Recent snow and strong wind have formed slabs at higher elevations. The most snow accumulated in the south of the region. The wind has blown from variable directions, so all aspects are suspect. Use added caution on south slopes if the sun is strong.

Use caution in freshly wind-loaded features, especially near ridge crests and in steep terrain.If triggered, wind slabs may step down to deeper layers and result in even larger avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

Two weak layers of surface hoar crystals are buried between 30 and 70 cm in the snowpack. The layers are most prominent around treeline and below treeline elevations.

Be aware of the potential for wide propagation.Avoid steep, open and/or sparsely treed slopes at and below treeline.Use conservative route selection, choose moderate angled terrain with low consequence.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible

Expected Size

1.5 - 2.5

Valid until: Feb 19th, 2019 2:00PM