Regions
Banff Yoho Kootenay.
Some decent propagation in wind loaded start zones on Mt Bosworth during avalanche control today. Winds are shifting to the east as of publishing: new windslabs in some different locations may form for Monday.
Weather Forecast
A low slipped south of the forecast area pushed by an arctic front over the prairies. 5 cm of snow is expected overnight while winds are shifting to the east and are expected to pick up to the strong range at mountain top as the polar air pushes west bringing a cold night and dry, cloudy day. Expect a return to the SW flow and flurries late Monday.
Snowpack Summary
Friday's storm brought 15-40cm with moderate S and W winds creating wind slabs in the alpine and into exposed areas at treeline. The March 15 suncrust is down 25-50cm on south east through west aspects and has been sensitive to skier triggering over the last few days. The mid- pack land basal layers have been dormant for the past while.
Avalanche Summary
Avalanche control work over the last two days on Mts Bourgeau, Whymper and Bosworth produced avalanches up to sz 2.5. These were limited to the recent storm snow 15 to 50cm deep with wind loading contributing to depths. On Mt Bosworth today, crowns up to 80m wide allowed slabs to entrain enough mass in steep tracks to run 2/3 path.
Confidence
Wind speed and direction is uncertain on Monday
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.