Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
The arctic ridge of high pressure will remain until Wednesday but is beginning to weaken. A series of weak frontal waves will move into northern BC and will be pushed into the southern interior by the arctic ridge. This will result in light, intermittent snowfall for the next few days. A major change in the weather is expected late Wednesday or Thursday when the arctic ridge breaks down and allows a low pressure system to enter southern BC with a westerly flow.Monday: Mostly cloudy, light snow flurries, treeline temperatures around -20C, moderate NW alpine windsTuesday: A mix of sun and cloud, light snow flurries, treeline temperatures around -15C, moderate NW alpine windsWednesday: Mostly cloudy, light snow flurries, treeline temperatures around -10C, winds switching to SW
Avalanche Summary
No natural avalanches reported since Thursday. Two ski cut avalanches reported on Saturday around Revelstoke. One size 1.5 storm slab on a NE aspect and one size 1 wind slab on a SW aspect at treeline.
Snowpack Summary
Snowpack depths are typically 100-140 cm at treeline elevation. The old storm snow (~30-60cm) overlies the late-November interface which typically consists of sun crusts on steep south facing slopes and surface hoar in sheltered areas. Some buried surface hoar has been reported on south aspect slopes near Revelstoke. These weak layers are expected to be persistent, although in many areas the upper slab is not yet stiff enough for slab avalanches. When temperatures rise, and we get additional snow, expect this interface to become a more dangerous problem. Strong NE winds after the storm caused reverse loading and wind slab formation on SE through W aspects in wind exposed areas. Lower snowpack layers include a surface hoar layer roughly 60cm above the ground and an early season rain crust at the base of the snowpack. While these layers have recently become inactive, residual risk of large, destructive avalanches exists, especially in areas with a thinner snowpack. The October crust can be found in the alpine on north aspects and the early November surface hoar appears to be isolated and drainage specific.
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.