Regions
Banff Yoho Kootenay.
Avalanche control is planned for Mt. Bosworth, Stephen and Field in Yoho and Mt. Whymper in Kootenay. Please no outdoor activities in these areas on Wed. Feb 19th.
Weather Forecast
A cold front will bring 5-15cm Tuesday overnight with moderate SW winds switching to NW as the system passes. We'll see a mix of sun and cloud with light flurries Wed and Thurs with a clearing trend towards the end of the week. Temps will cool to -10/-15 with the passing of the front on Wed AM.
Snowpack Summary
30 -70 cm of storm snow is settling and being blown into a cohesive slab which is overlying the weak Feb. 10th interface. This interface is a mix of sun crust, facets and surface hoar and will likely persist for a while. Additionally, SW winds have created wind slabs in lee alpine terrain which trigger easily and step down to the Feb. 10th layer.
Avalanche Summary
Evidence of a small cycle was observed today to size 3 as the recent storm snow has started to become a more cohesive slab. Notable events were multiple skiier triggered and explosives controlled avalanches to size 2.5 at the Lake Louise Ski Area and a size 3 natural off Mt. Wapta that buried the Tak Falls road with 1-2m of debris.
Confidence
Due to the number and quality of field observations
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.