Regions
Banff Yoho Kootenay.
Large and destructive avalanches are likely. Step way back and avoid avalanche terrain. Avalanche control is planned for Mt. Bosworth, Mt. Dennis Mt. Field and Mt. Whymper tomorrow. No activity permitted in these areas.
Weather Forecast
Wednesday will present a slight cooling trend and an easing of precipitation. However, Thursday will see the temperatures rise and the precip return. By Friday the storm will intensify a deposit up to another 30cm by the end of the weekend. Obviously, this will contribute to a rise in the danger rating.
Snowpack Summary
Recent storms have deposited 45-85cm of storm snow in the last 7 days. Increasing wind and steady snowfall today are loading 3 persistent weak layers of surface hoar and facets in the upper half of the snowpack: Jan 16 down 25-45cm; Jan 6 down 35-55cm; and Dec15 down 45-80cm. In snowpits, these layers are giving sudden test results.
Avalanche Summary
A major cycle is upon us. Avalanche control today produced results up to size 3.5 with deep fractures and wide propagations. Basically, avalanches could been seen anywhere a forecaster looked today.
Confidence
Due to the quality of field observations on Monday
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.