Avalanche Forecast

Issued: Apr 4th, 2018 4:44PM

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

ghelgeson, Avalanche Canada

Purcells.

A variety of weak layers continue to produce human triggered avalanches. We're still managing a midwinter snowpack that requires thoughtful terrain selection.

Summary

Confidence

High -

Weather Forecast

A seasonably cool weather pattern is expected to stick around for the foreseeable future and it looks like we will pick up a few centimeters of snow every day through the weekend too. THURSDAY: Scattered cloud cover, freezing level beginning near valley bottom rising to about 1000 m, light variable wind, 1 to 2 cm of snow possible. FRIDAY: Broken cloud cover, freezing level beginning near valley bottom rising to about 1000 m, light southerly wind at treeline, moderate westerly wind at ridgetop, 1 to 2 cm of snow possible. SATURDAY: Broken cloud cover, freezing level beginning near valley bottom rising to about 1000 m, light southerly wind, 1 to 3 cm of snow possible.

Avalanche Summary

On Tuesday a small avalanche was triggered by a skier on a northeast facing slope at 2200 m. The size 1 avalanche failed on the late March interface. Control work produced avalanches from size 2 to 3 on north/northeast facing features above 2400 m that likely ran on the late March interface as well.On Saturday a skier triggered a large slab avalanche (size 2.5) on a south aspect at 2600 m. The avalanche failed on a buried sun crust 150-200 cm below the surface. Another large (size 2.5) wind slab released naturally from a steep southeast-facing alpine slope in the St. Mary's area. Explosives control in the northern half of the region produced numerous storm slabs ranging from size 1.5-2.5 at treeline and alpine elevations. Crown fractures ranged from 30-100 cm. All aspects were represented in results, with the majority of activity focused on northeast to northwest aspects in the alpine.

Snowpack Summary

Tuesday night's storm brought up to 8 cm of new snow with very little wind.Storms over the past week brought variable snowfall totals of 20-80 cm to the region, with areas to the south of the region seeing the deepest accumulations. This storm snow sits on a persistent weak layer buried in late March that consist of crusts below 1900 m and on south aspects, and surface hoar on shaded aspects at higher elevations. Other slightly deeper surface hoar/facet layers have been reported on shaded aspects at higher elevations and may be found approximately 40-90 cm below the surface.Deeper persistent weak layers from mid-late February as well as January and December layers, are still being monitored by professional observers, but are generally considered dormant. Facets also linger at the base of the snowpack.

Problems

Persistent Slabs

A weak layer of crust and surface hoar has been buried by a variable 20-80 cm of storm snow and has shown continued reactivity since the last storm. Manage the uncertainty around triggering this layer by sticking to lower angle, supported slopes.

Use conservative route selection, choose moderate angled and supported terrain with low consequence.Minimize exposure to steep south-facing alpine slopes, where buried crust may be preserved.Use caution around sheltered steep or convex slopes where buried surface hoar may be preserved.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 2.5

Wind Slabs

Light new snow has been redistributed by variable winds into thin wind slabs on a variety of aspects. Slabs have also been noted forming above weak layers like crust and surface hoar. Deeper slabs are likely to be found in the south of the region.

Wind slabs bay be touchier in areas where they overlie crust or surface hoar.Be especially careful with wind loaded pockets near ridge crests and roll-overs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Apr 5th, 2018 2:00PM