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Avalanche Forecast

Archived

Mar 25th, 2017–Mar 26th, 2017

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Northwest Coastal.

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

Confidence

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

Weather Forecast

We'll have a brief lull in the action on Sunday before things pick up again Monday afternoon into Tuesday. Winter's not done yet! SUNDAY: Lingering flurries, moderate southeast wind, freezing levels 900m, alpine temperature around -5 C. MONDAY: Snow in the afternoon (10cm). Strong south wind, freezing level around 1100 m with alpine temperature around -3 C. TUESDAY: 15-25 cm possible Monday overnight into Tuesday afternoon, strong south wind, freezing levels 1100m.

Avalanche Summary

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.Also on Friday, a Size 2.5 persistent slab (2m deep) was reported running out of steep terrain. On Thursday, skiers were able to trigger a small Size 1 wind slab (10cm thick), running on the March 22nd surface hoar layer.Reports from Tuesday indicate the persistent slab problem is alive throughout the region. A few natural size 2-2.5 avalanches were triggered in the Bear Pass / Stewart area by solar input and cornices. A skier also remotely triggered a size 2 avalanche on the February facet/crust interface on a moraine feature around 1150 m (40 cm deep). Similar activity was reported the previous day, including a size 3 avalanche that was remotely triggered from flat terrain by a snowmobiler north of Stewart.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 and cornices are forming in the lee of exposed terrain as yet another March storm has brought 5-15cm of new snow (20cm near Stewart) and moderate southwest 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.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.