Regions
Banff Yoho Kootenay.
Just how sensitive the snowpack is to a trigger became quite clear this weekend when the winds picked up. Fresh windslabs have formed and the slab over the weak midpack has developed further. Cautious terrain selection has become even more important
Weather Forecast
The jet stream that has been directly over our heads for the last few days will shift further south tonight. Cold northern air will return with north winds at upper elevations and plunging temperatures pushing away some remaining cloud and moisture. Clear, Calm and Cold by Wednesday night. This state of affairs looks to last until Friday.
Snowpack Summary
Strong to Extreme S and W winds continue to redistribute the 5 to 10 cm of new snow and the 10 to 20 cm that fell last week. Isolated surface hoar may be found buried in sheltered locations. Generally the midpack is weak at TL and above and the entire snowpack is weak BTL. Near the divide, deeper snow-packs are a bit stronger and more supportive.
Avalanche Summary
There is evidence of a avalanche cycle over the weekend and continuing today with windslabs and a few larger events involving the midpack / basal layers. Most of these events could be attributed to the wind redistributing recent snowfall and speak to the fragile nature of the snowpack: it required only small inputs to generate natural avalanches.
Confidence
Due to the number of field observations
Problems
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
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.