Regions
Kootenay Boundary.
Persistent slab problems are not obvious and tricky to manage. This problem is mostly found in open glades and gullies at treeline and below and its just waiting for a trigger.
Confidence
High - The weather pattern is stable on Thursday
Weather Forecast
Increasing cloud cover and light snow amounts are forecast with the incoming weather system. The weekend will remain cold.THURSDAY: Cloudy with sunny periods and isolated flurries. Alpine temperatures near -13 with light ridgetop winds from the southwest.FRIDAY: Cloudy with snow amounts 5-10 cm. Alpine temperatures near -10 and ridgetop winds moderate from the southeast. SATURDAY: Cloudy with snow amounts 5-10 cm. Alpine temperatures near -19 and ridgetop winds moderate from the East.
Avalanche Summary
On Tuesday, several skier triggered avalanches were reported. These failed on the surface hoar layer down 20-30 cm below the recent storm snow. They were easily triggered by the weight of a person on a variety of aspects from 1900-2100 m. Natural dry loose sluffing was noted from steeper terrain features. With a fairly benign weather pattern natural avalanche activity will be far and few on Thursday, however, human triggers will remain likely.
Snowpack Summary
10-30 cm of snow that fell late last week now sits on variety of snow surfaces, including buried wind crust on westerly aspects, sun crust on southerly aspects to mountain top and weak feathery surface hoar crystals in sheltered areas at treeline and below. The snowpack now hosts two predominant buried surface hoar layers. The one that was buried on February 1st seems to be more reactive to human triggers than the one buried deeper down (40-80 cm). This deeper layer of surface hoar may be most reactive below treeline on shady aspects but doesn't seem to be a widespread problem in the region. The mid-pack is generally well-settled and strong.
Problems
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.
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.