Avalanche Forecast

Issued: Mar 7th, 2017 3:44PM

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

Avalanche Canada mgrist, Avalanche Canada

It's time to dial back terrain choices at all elevations:  There is a lot of uncertainty surrounding the buried weak layer underneath the persistent slab. This interface has remained problematic longer than we'd typically expect in this region.

Summary

Confidence

Moderate - The weather pattern is stable

Weather Forecast

We're looking at occasional flurries and then cold and clear toward the end of the forecast period. WEDNESDAY: Flurries with 5-10 cm of new snow, 20-30 km/h east winds, alpine temperatures around -12 C. THURSDAY: Cloudy with scattered flurries and up to 3-5 cm of new snow, 30-50 km/h east winds, alpine temperatures around -16 C. FRIDAY: Sunny with cloudy periods, 20-40 km/h southeast winds, alpine temperatures around -16 C.

Avalanche Summary

On Monday two avalanches were simultaneously remote-triggered below treeline west of Terrace. See here for the excellent details in the Facebook post.  Crown heights were 50-80cms.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.On Saturday several storm slabs sized 1.5 to 2.5 (some remote triggered) were reported on north through east aspects, between 1100 and 1400m elevation.Conditions will remain touchy as the recent storm snow settles and stiffens.

Snowpack Summary

We've had 5-10cm of low density snow falling for each of the past few days, which has brought recent storm snow totals to 70-100 cm. All this snow has buried a variety of old snow surfaces including surface hoar, facets, crusts, stiff wind slabs and a melt-freeze crust below 1600 m. The storm snow remains very reactive on this interface, resulting in widespread whumpfing and cracking in flat terrain. Moreover, we've had reports of sudden, propagation-likely test results down 50-85 cm 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
Storm snow from the last week has consolidated into a slab 50-85cm in depth that is poorly bonded to the old surface due to a persistent buried weak layer. These slow to heal slabs are most likely to be triggered in wind exposed terrain.
Heads up: Persistent slabs will remain a problem for longer than usual after the storm.Don't let the lure of deep powder pull you into high consequence terrain.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Valid until: Mar 8th, 2017 2:00PM

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