Avalanche Forecast

Issued: Mar 8th, 2017 4:20PM

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

Avalanche Canada jlammers, Avalanche Canada

It's time to dial back terrain choices at all elevation bands. A buried persistent weak layer has created the potential for surprisingly large avalanches.

Summary

Confidence

Moderate -

Weather Forecast

Expect a mix of sun and cloud for the forecast period. Ridgetop winds should remain generally light to moderate from the east with alpine temperatures sitting at about -15.

Avalanche Summary

On Monday two avalanches were simultaneously remotey-triggered below treeline west of Terrace. See here for the excellent details in the Facebook post. These avalanches speak to the touchy persistent avalanche problem in the region.We had reports of two rider-triggered wind slab avalanches (Size 1.5 and 2.0) southwest of Terrace on Sunday. In both cases the crown height was 50cm and shooting cracks were also reported in mellow terrain. There was a remote-triggered Size 1 in the Shames backcountry, also with a 50cm crown, running on a weak facet layer.Conditions will remain touchy as the recent storm snow settles into a cohesive slab over top of the late February persistent weak layer.

Snowpack Summary

On Tuesday night the region received between 5-40cm of new snow with the greatest accumulations occurring in the south of the region. Southwest winds are expected to have redistributed this new snow forming fresh wind slabs in exposed lee terrain.  70-120 cm below the surface you'll find a variety of old surfaces which were buried in late February. These surfaces include surface hoar, facets, crusts, stiff wind slabs and a melt-freeze crust below 1600 m. The overlying slab remains very reactive on this interface which was buried in late February, resulting in widespread whumpfing and cracking in flat terrain. Moreover, we've had reports of sudden, propagation-likely test results on weak facets or the late-February crust / surface hoar.Below this interface the snowpack is generally settled and strong with the exception in shallow snowpack areas around Bear Pass and Ningunsaw where basal facets remain an ongoing concern.

Problems

Persistent Slabs

An icon showing Persistent Slabs
A mix of persistent weak crystals lurk up to 120cm below the surface, and have the potential for surprisingly large avalanches. Conservative terrain selection remains critical for the foreseeable future.
Use conservative route selection, choose moderate angled and supported terrain with low consequence.Be aware of the potential for surprisingly large avalanches due to deeply buried weak layers.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Wind Slabs

An icon showing Wind Slabs
Recent snow accumulations are expected to have been shifted into fresh wind slabs in exposed lee terrain. These surface instabilities have the potential to step-down to deep, more destructive layers.
Be cautious as you transition into wind affected terrain.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Mar 9th, 2017 2:00PM

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