Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain
Weather Forecast
The rather largo weather pattern that has been in place for the last week is being swept out of the province Monday setting the stage for an active weather week influenced by SW flow for the southern interior. Monday Evening: freezing level tops out around 2000m Monday evening as precip begins to fall. 10mm of water are expected, most of which will fall as rain as high as 1800m. Alpine elevations should receive 15 or so cm of snow. Winds should be moderate out of the NE, switching SW overnight. Tuesday: Freezing levels remain near 1500m, trace of precip expected. Treeline winds light out of the S, SE, Alpine winds Moderate, SW. Wednesday: Freezing level 1500m, 5mm water expected during the day. Winds increasing to moderate SW at treeline, moderate gusting strong SW in the Alpine. Look for clearing skies Thursday AM with precipitation expected to start back up in the afternoon.
Avalanche Summary
Lots of wet activity on Sunday, mostly wet point releases, sluffing & pinwheeling to size 1.5. It's interesting to note that a glide crack released out of steep ,rocky, east facing terrain in the Revelstoke area resulting in a size 2.5 avalanche. A report came in from Glacier Park Saturday of a remotely triggered large avalanche on a north aspect of Mt Tupper. The group of ski tourers had a large settlement on a ridge, and the adjacent slope failed down about 150 cm. Large remotely triggered avalanches have become less frequent, but seam to occur every couple of days.
Snowpack Summary
Wind slabs in the alpine and at treeline are becoming less reactive. A melt-freeze crust exists from valley floor into the alpine on solar aspects. A key concern is a persistent weak layer of buried surface hoar from mid-February that is buried 1-2 m deep. Snowpack tests give sudden "pops" results on this layer in some areas, indicating the ongoing potential for very large avalanches. Because the layer is so deeply buried, it's unlikely to fail without a large trigger (e.g. cornice fall or explosive). However, there's always the chance of someone stumbling across a sweet spot, particularly in shallow snowpack areas. Solar warming could also destabilize the overlying snowpack, with the potential for step-downs or cornice triggering on this layer.
Problems
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.