Avalanche Forecast

Issued: Jan 25th, 2016 8:49AM

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

rbuhler, Avalanche Canada

Purcells.

The current conditions require restraint and conservative decision-making. Triggering the weak layer is getting more difficult but large avalanches, even from relatively low-angle slopes, remain possible. New wind slabs may also form on Tuesday.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

A weak storm pulse is expected to bring up to 5cm of new snowfall to the region on Tuesday. Freezing levels are expected to be around 1500m and alpine winds are forecast to be moderate to strong from the southwest. A mix of sun and cloud is expected for Wednesday with freezing levels reaching around 1500m and light to moderate southwest winds in the alpine. A more substantial storm front is expected to reach the region on Wednesday night or Thursday morning. 10-20cm of snowfall is currently being forecast with freezing levels around 1700m and strong southwest winds.

Avalanche Summary

On Sunday, numerous avalanches were reported including natural, explosive, and skier triggered. Explosives triggered persistent slabs size 2-3 which were failing on the early January surface hoar typically down 40-60cm. A skier remotely triggered a size 1 slab from 2m away. This occurred at 1750m on an east aspect and the slab was 80cm thick. Skiers reportedly cut a cornice at 2100m on a northeast aspect which subsequently triggered a size 2.5 wind slab avalanche. A couple natural avalanches were reported on Sunday but most of the natural avalanches occurred on Friday and Saturday due to storm loading. While natural activity has tapered off since Saturday, the persistent slab is expected to remain reactive to human triggering for several more days. New wind slabs may form on Tuesday with the progression of the weak storm system.

Snowpack Summary

Conditions are widely variable across the Purcells. Wind slabs and storm slabs have developed at treeline and alpine elevations. In some areas, these overlie a surface hoar or crust/facet interface from early January and may be easily triggered by a skier or sledder. Reports indicate this persistent weak layer is now typically down 40 to 60cm in most areas and appears to be quite touchy in some parts of the region. A more deeply buried layer of surface hoar from December is now considered dormant. In general, the lower snowpack is well settled and strong.

Problems

Persistent Slabs

Large avalanches have been failing on a buried persistent weak layer down 40-60 cm. This problem will likely remain sensitive to human triggers for the next few days.

Be aware of the potential for remote triggers and wide propagations due to a layer of buried surface hoar. >Avoid open slopes and convex rolls at and below treeline, and north-facing alpine slopes, where buried surface hoar may be preserved. >

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 5

Wind Slabs

New wind slabs may form in leeward features on Tuesday. It may still be possible to trigger deep older wind slabs in exposed lee and cross-loaded terrain near ridge crests.

Be cautious as you transition into wind affected terrain. >Use ridges or ribs to avoid pockets of wind loaded snow. >Avoid freshly wind loaded features. >

Aspects: North, North East, East, South East.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Valid until: Jan 26th, 2016 2:00PM