Avalanche Forecast

Issued: Feb 1st, 2019 4:51PM

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

kdevine, Avalanche Canada

Purcells.

New snow and wind will mean that storm slabs are to be expected, and will likely be reactive to human triggering, especially in wind loaded areas.

Summary

Confidence

Moderate -

Weather Forecast

FRIDAY NIGHT - Flurries, 5-10 cm / southwest winds, 30-60 km/h / alpine low temperature near -5SATURDAY - Cloudy with sunny periods and scattered flurries, 3 cm / southwest winds 20-40 km/h / alpine high temperature near -5SUNDAY - Mainly cloudy with isolated flurries / southeast winds 10-15 km/h / alpine high temperature near -10MONDAY - Mainly cloudy / northeast winds, 10-15 km/h / alpine high temperature near -16

Avalanche Summary

On Thursday, a few natural and human triggered avalanches to size 1.5 were reported on all aspects around treeline. These reportedly failed on the persistent weak layer that was buried in mid January.There is a great MIN report from January 22nd that shows a natural avalanche (size 3.5) in International Basin, on the deep persistent layer. Check it out here. While this is an old observation, it is relevant as this layer is still lurking, and may catch people off guard.

Snowpack Summary

10-30 cm of new snow has fallen in the region since Thursday. This new snow sits wind slab, surface hoar (feathery crystals), facets (sugary snow) and a crust on sun-exposed slopes.Â A persistent weak layer that was buried in mid January is now buried 20-50 cm. This layer consists primarily of surface hoar, however there is also a crust associated with it on sun-exposed slopes. This layer has been most reactive at treeline and below.The base of the snowpack has a deep persistent weak layer near the ground. This layer consists of facets over a crust. This weak interface continues to produce large and destructive avalanches that are sporadic in nature, and very difficult to predict.Â This layer 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 the kind of terrain to be wary of.

Problems

Storm Slabs

Up to 30 cm of new snow has fallen in the region and will likely be reactive to human triggers, especially in wind loaded areas.

If triggered, storm slabs may step down to deeper layers and result in large avalanches.Be careful with wind loaded pockets, especially near ridge crests and roll-overs.Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Deep Persistent Slabs

The last avalanche observed on the weak facet/crust interface at the ground was on Monday and human triggered avalanches remain possible. Is it a 1 in 100 slope, or a 1 in 1000 slope problem now? We're not sure and this is what makes it so tricky.

Minimize overhead exposure; avalanches triggered by cornice fall may be large and destructive.Use caution on alpine slopes, especially around thin areas that may propagate to deep instabilities.Avoid making assumptions about this layer based on aggressive tracks on adjacent slopes.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 4

Persistent Slabs

20-50 cm of snow now sits on a weak layer of surface hoar and crust. This layer has been most reactive at lower elevations.

Watch for signs of instability such as whumpfing, shooting cracks and recent avalanches.Avoid convex rolls at and below treeline where buried surface hoar may be preserved.Use extra caution around steep open terrain features, such as cutblocks, gullies and cutbanks.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Feb 2nd, 2019 2:00PM