Regions
Northwest Coastal.
The persistent slab problem still needs time to stabilize. Evaluate the terrain and snowpack carefully and stay aware of overhead hazards.
Confidence
High - Due to the number and quality of field observations
Weather Forecast
FRIDAY: Unsettled weather with flurries bringing 5-10 cm of snow, moderate south wind, alpine temperature around -3 C.SATURDAY: More flurries with another 10-15 cm, strong south wind, alpine temperature around -6 C.SUNDAY: Lingering flurries, moderate southeast wind, alpine temperature around -6 C.
Avalanche Summary
No new avalanches were reported on Wednesday, but reports from Tuesday indicate the persistent slab problem is alive and well 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 ongoing persistent slab problem, the incoming weather pattern is looking to continually build fresh wind slabs.
Snowpack Summary
Fresh wind slabs and cornices are forming in the lee of exposed terrain as unsettled weather brings small amounts of new snow and moderate winds. Recent warming and sun have likely left 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 50-100 cm deep and is still reactive throughout the region, especially in shallower areas around Stewart and Bear Pass.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.