Avalanche Forecast

Issued: Feb 17th, 2019 4:00PM

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.

mconlan, Avalanche Canada

Purcells.

Slabs that formed from recent snow and wind 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.

Summary

Confidence

High -

Weather Forecast

SUNDAY NIGHT: Clear skies, light to moderate north wind, alpine temperature -20 C.MONDAY: Clear skies, light to moderate northwest wind, alpine temperature -17 C.TUESDAY: Cloudy with light snowfall, accumulation 1 to 3 cm, light to moderate west wind, alpine temperature -15 C.WEDNESDAY: Cloudy with light snowfall, accumulation 1 to 3 cm, light northeast wind, alpine temperature -15 C.

Avalanche Summary

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 strong, variable wind, creating touchy wind slabs in exposed areas. In the south and west of the region, recent storm 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.

If triggered, wind slabs may step down to deeper layers and result in even larger avalanches.Use caution in freshly wind-loaded features, especially near ridge crests and in steep terrain.Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.

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.

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

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible

Expected Size

1.5 - 2.5

Valid until: Feb 18th, 2019 2:00PM