Avalanche danger will increase in the afternoon with strong solar input and warming temperatures. Concern for persistent slab problems is on the rise.See the Forecaster's Blog for more: http://www.avalanche.ca/blogs/2018-03-09-first-big-warm-up
Confidence
Moderate - Timing or intensity of solar radiation is uncertain
Weather Forecast
Sunny and warm until the start of our next weather system on Wednesday. MONDAY: Sunny. Light southeast winds. Freezing level rising to 2200 metres with alpine high temperatures around +2.TUESDAY: Mainly sunny. Light southeast winds, increasing over the day. Freezing level to 2500 metres with alpine high temperatures of +3.WEDNESDAY: Cloudy with isolated flurries in the afternoon. Light south winds. Freezing level near 2000 metres with alpine high temperatures of +1.
Avalanche Summary
A widespread natural avalanche cycle to size 3 was reported on Saturday. These avalanches were primarily wet loose avalanches on sunny aspects, however, some did step down to the mid-February layer on southerly aspects. Reports from Friday included observations of numerous storm slabs and wind slabs that ran from size 1.5 to 2.5. These were triggered naturally as well as with ski cutting and all aspects and elevations were represented. Avalanche activity is expected to increase as we move into a period of intense sun and prolonged warming. Predictable loose wet avalanches from steep, sunny terrain should be easy to manage. A trickier problem will emerge as warmth penetrates into the snowpack to tickle deeper persistent weak layers. This will be a time to avoid exposure to large sunny features and keep well away from corniced slopes.
Snowpack Summary
15-25 cm of snow from Thursday into Friday sits on sun crusts on solar aspects and well-settled storm snow on more northerly aspects. Several other sun crust layers may be found within the older storm snow on solar aspects.A couple of layers buried in mid to late February (down around 60-110 cm) are variably reactive, but both have the potential to create surprisingly large avalanches if triggered. Initially, these interfaces were most reactive on solar aspects, where they present as buried sun crusts. However, persistent slabs have been triggered on shady aspects too, where surface hoar and/or facets exist.Deeper persistent weak layers from January and December are generally considered dormant, but could wake up with forecast warming, a surface avalanche stepping down, cornice fall, or a human trigger in a shallow or variable-depth snowpack area. These layers consist of sun crust, surface hoar and/or facets.
Problems
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.
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.