Avalanche Forecast

Issued: Jan 31st, 2019 3:52PM

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

mconlan, Avalanche Canada

South Rockies.

Continue to make cautious decisions due to the weak layers buried in the snowpack.

Summary

Confidence

High -

Weather Forecast

THURSDAY NIGHT: Mostly cloudy, freezing level 1000 m.FRIDAY: Cloudy with light snowfall, accumulation 5 cm, moderate to strong southwest winds, alpine temperature -3 C, freezing level 1500 m.SATURDAY: Cloudy with light snowfall, accumulation 5 to 15 cm, light southwest winds, alpine temperature -3 C, freezing level below valley bottom.SUNDAY: Cloudy with light snowfall, accumulation 5 cm, light east winds, alpine temperature -24 C, freezing level below valley bottom.

Avalanche Summary

On Wednesday, a skier triggered a small slab at treeline on a west to northwesterly aspect. On Tuesday, a small avalanche triggered by a snowmobile was observed, releasing on the surface hoar layer described in the Snowpack Summary. Shooting cracks were also observed, suggesting instability with that layer.

Snowpack Summary

New snow will begin to fall on Friday with an incoming storm. The snow will fall with strong southwest winds, so expect wind slabs to begin to form in lee and cross-loaded terrain features.The new snow will continue to build a slab over a weak layer of feathery surface hoar crystals, which is buried about 10 to 30 cm. The surface hoar is most prominent between 1500 and 1900 m but has been found up to 2100 m. On south aspects, the snow overlies a melt-freeze crust to the top of the mountains.The middle of the snowpack is generally consolidated. The bottom half of the snowpack is unconsolidated and composed of weak and sugary faceted grains.

Problems

Persistent Slabs

Around 10 to 30 cm of snow sits above a weak layer of feathery surface hoar crystals, which is best preserved in shaded and sheltered areas between 1500 m and 1900 m. On southerly aspects, the snow sits on a hard melt-freeze crust.

Be careful with wind-loaded pockets, especially near ridge crests and roll-overs.Be very cautious in open terrain features, such as cutblocks, gullies, and cutbanks.If triggered, slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 1.5

Deep Persistent Slabs

The bottom of the snowpack consists of weak and sugary faceted snow. There is a relatively low likelihood of triggering this layer at the moment, but the consequences remain high, as avalanches on this layer will be large and destructive.

Avoid steep, rocky terrain and shallow snowpack areas where triggering deep layers is more likely.Watch for signs of instability such as whumpfing, cracking, or recent avalanches.Use conservative route selection, such as moderate-angled and smooth terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Feb 1st, 2019 2:00PM