Saturday's weather will test the snowpack and a natural avalanche cycle is expected to occur. Northern parts of the region may see conditions similar to adjacent regions where danger has been rated Extreme.
Weather Forecast
Saturday: Flurries bringing 10-20 cm of new snow to higher elevations with a possibility of localized enhanced amounts. Rain below about 1800 metres. Strong to extreme southwest winds. Freezing level to 2200 metres with alpine temperatures of 0 to +1. Sunday: Sunny with cloudy periods. Moderate west winds. Freezing level to 1400 metres with alpine temperatures around -9. Monday: A mix of sun and cloud. Light southeast winds. Freezing level to 1700 metres with alpine temperatures of -6.
Avalanche Summary
A report from the Crowsnest area showed a natural Size 3.5 deep persistent slab that began as a ridgetop wind slab release before stepping down to ground as it descended its track. Looking forward, another dose of wind and snow will see wind slabs continue to develop in the alpine above the high freezing levels while rain soaks the snowpack again at lower elevations. The potential for deep persistent avalanches is very real concern for Saturday.
Snowpack Summary
An unexpected 15 cm of new snow fell over the south of the region on Thursday night, with a trace to 5 cm accumulating in most of the region. Below the new snow, recent warm, wet, and windy weather has formed fresh wind slabs at higher elevations while saturating the snowpack with rain below treeline. The rain soaked snow has refrozen into a crust that may be supportive at higher elevations. Regular snowfall throughout early March has seen roughly 50-90 cm of snow accumulate above the crust and facet interfaces from February. In some areas this storm snow may have a poor bond to these interfaces. Aside from that uncertainty, the mid-pack in the region is generally strong. With that said, the bottom third of the snowpack is composed of weak sugary facets roughly 1-1.5 metres deep. The potential for full-depth avalanches over this basal weakness remains a real concern, especially as ongoing loading and warming continue to stress the snowpack.
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.
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.