Weather on Friday looks quite variable across the Purcells. In the south and west, increased loading from snow and wind could drive danger ratings higher than posted.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Friday brings another 5-15 cm snow, moderate SW winds and freezing levels around 1500 m. Through the weekend, expect mainly light winds, cool temperatures, cloudy skies and a few flurries.For more details check out https://avalanche.ca/weather.
Avalanche Summary
On Wednesday, explosives triggered three size 2 wind slabs. On Tuesday, skiers who ventured onto a steep alpine feature in a permanently closed area within a ski area triggered a size 1.5 wind slab.On Monday, several small slabs were triggered by skiers, including three that were remotely triggered. These were either on wind-loaded features at and above treeline, or in openings at low elevations, where buried surface hoar is largest and most reactive. Snow and wind this week could overload the persistent weak layer in some parts of the region.
Snowpack Summary
Conditions are variable across the Purcells. New wind slabs are developing at treeline and alpine elevations. In some areas, these overlie a surface hoar or crust interface and may be extra touchy. The persistent weak layer from early January is around 20-40 cm down and has not yet reached tipping point in many parts of the region. With warming, snow and wind forecast on Friday, a consolidated persistent slab could form. Operators are also still keeping an eye on a more deeply buried layer of surface hoar from December, which is now considered dormant or unreactive. In general, the mid and lower snowpack are well settled and strong.
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.