Touchy conditions exist in the North of the region with the potential for large and destructive avalanches.
Confidence
Fair - Due to the number of field observations on Sunday
Weather Forecast
Scattered convective snowfall (up to 10cm) is expected on Monday as a cold front moves across the region. By late Tuesday a short-lived ridge will bring clearing. On Wednesday a more organized warm and wet frontal system will bring rain to most elevations. Ridgetop winds are expected to be moderate from the southwest with Monday's snowfall, otherwise remaining light. Freezing levels should hover around 1500m on Monday and Tuesday, and then climb to about 2500m with Wednesday's system.
Avalanche Summary
Over the past week, there have been a number of avalanches to size 2.5 occurring on the March 11 persistent weak layer. Some avalanches have occurred naturally, or remotely from distances of up to 100m. Hot spots for avalanche activity seem to include the Duffey Lake area, the Birkenhead drainage, the Hurley and the South Chilcotins. Snow and wind on Monday will likely add a round of wind slab activity to the mix. But it will also add load to the March layer, potentially adding to its reactivity and destructive potential.
Snowpack Summary
New wind slabs have formed in response to recent wind, snowfall and warm temperatures. At lower elevations, rain has saturated the snowpack. Cornices may also be fragile. A touchy crust/facet persistent weak layer, buried up to 60 cm down, has been reactive producing easy test results at upper treeline and alpine elevations, especially in the north of the region (see avalanche summary). Avalanche problems associated with this layer may linger for a while with the potential for surprisingly large and destructive avalanches. Below this, the snowpack is reported to be generally well-settled and strong.
Problems
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.
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.