Avalanche Forecast

Issued: Mar 26th, 2017 4:56PM

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

mgrist, Avalanche Canada

Northwest Coastal.

With the new snow load, persistent slab problems continue to rear their ugly head. Conservative terrain use is essential & stay aware of overhead hazards.

Summary

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

We're looking at a series of systems impacting the region throughout the forecast period. The winter storm train keeps rolling into town! MONDAY: Snow in the afternoon (10cm). Strong south wind, freezing level around 1100 m with alpine temperature around -3 C. TUESDAY: 15-25 cm Monday overnight into Tuesday afternoon, strong southwest wind, freezing levels 1200m. WEDNESDAY: Lingering flurries (5-10 cm possible) moderate south wind, freezing levels 1100m, alpine temperature around -4 C.

Avalanche Summary

On Sunday, a machine-triggered Size 3 (with crown averaging 1.5m thick) was reported north of Terrace on a northwest aspect near 1400m. The slab is suspected to have run on the late February interface.On Saturday, several wind slabs to Size 1.5 were reported on (east) northeast aspects in the north of the region. On Friday, a spooky Size 3.5 persistent slab with impressive propagation was remote-triggered north of Terrace at 1500m elevation. See here for more details in this excellent post.A significant concern remains the potential for persistent slab avalanches triggered by people. See the forecaster blog for advice on managing a low probability - high consequence problem (here) and the accompanying photos (here).In addition to the daunting persistent slab problem, the incoming weather pattern is looking to continually build fresh storm slabs.

Snowpack Summary

Fresh storm slabs (up to 40cm thick) developed at treeline and above, while cornices grew larger during another March storm: Weekend totals brought 10-20cm of new snow and moderate southwest / southeast winds. This recent snow sits on a crust on solar aspects and below 1000 m.Snow may still be poorly bonded to a 40 cm deep crust and surface hoar interface from mid-March, however, the late-February interface has been the more troublesome persistent layer. It's composed of facets, crust, and surface hoar roughly 70-140 cm deep and is still reactive throughout the region, especially in shallower areas around Stewart and Bear Pass. See the Avalanche Summary above for a good example of this persistent problem re-awakening.

Problems

Storm Slabs

New snow may overload wind slabs sitting on the March 22nd surface hoar layer. Conservative terrain use is essential and manage your overhead exposure.

If triggered, the storm slabs may step down to deeper layers resulting in large avalanches.Be aware of the potential for wide propagations due to the presence of underlying windslabs.The new snow will require several days to settle and stabilize.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Persistent Slabs

A weak facet/crust layer from late February has produced several large human triggered avalanches the past few days. Triggering this layer is most likely in shallower areas, but a small wind slab or cornice fall could act as a natural trigger.

Avoid steep convexities or areas with a thin or variable snowpack.Use conservative route selection, choose moderate angled and supported terrain with low consequence.Remote triggering is a concern, watch out for adjacent slopes.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 4

Valid until: Mar 27th, 2017 2:00PM