Regions
Banff Yoho Kootenay.
By definition, the danger rating is moderate. However, the Dec 15th layer continues to be very sporadic and temperamental in its reactivity and distribution. Exercise caution near steep rolls at treeline.
Weather Forecast
The temperature inversion will continue until Tuesday morning. Expect alpine temperatures to remain near 0 degrees. A cooling trend is expected thereafter. Cloud cover and the start of light precip will begin late on Tuesday. Accumulations of up to 10cm are expected by the end of Thursday. Wind will pick up to moderate from the SW throughout Tues.
Snowpack Summary
Continued warm alpine temperatures and clear skies moistening the upper snowpack on steep S-W aspects. 30-50cm over the Dec.15 persistent weak layer of facets and surface hoar. This Dec 15th layer is becoming reactive to skiers at treeline and above and producing easy to moderate snowpack test results. Below this is a heavily faceted snowpack.
Avalanche Summary
Avalanche control produced results up to size 2.5 today on Hwy 93S and the Sunshine Road. The larger avalanches were produced on uniform terrain features at treeline where the Dec 15th surface hoar was present. Overall, the control mission produced 'hit and miss' results, which speaks to the variability and distribution of the Dec 15th layer.
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.