Warmer temperatures and rising freezing levels starting late Friday will make a more cohesive, easier-to-trigger slab above the weak interface. Pay attention to rapid change to the snow surface with temperature warming and direct solar radiation.
Confidence
Moderate - Freezing levels are uncertain on Saturday
Weather Forecast
THURSDAY NIGHT: Mainly cloudy with isolated flurries, moderate west winds, alpine temperature -6 C, freezing level at valley bottom.FRIDAY: Mainly cloudy with flurries, snow accumulation up to 8 cm, moderate to strong west winds, alpine temperature -1 C, freezing level at 1500 m.SATURDAY: Cloudy with isolated flurries, strong winds from west, alpine temperature +1 C, freezing level rising up to 1900-2100 m with a weak temperature inversion.SUNDAY: A mix of sun and clouds with isolated flurries, moderate to strong winds northwest winds, alpine temperature -3 C, freezing level at 1300 m.
Avalanche Summary
A few natural wind slabs, storm slabs and dry loose avalanches up to size 2.5 have been reported Wednesday on steep slopes of all aspects in the alpine.
Snowpack Summary
15-30 cm of snow sits above a layer of large surface hoar crystals and sun crust. In areas that have had wind effect the recent snow has been settling into a thin but reactive slab above this weak layer, with enhanced reactivity noted at elevations between 1500-1800 metres. In sheltered areas the snow is faceting and lacks cohesion above this layer which is only reactive as dry loose sluffing. Forecasted warmer temperatures starting late Friday will change this and promote increased cohesion in the upper snowpack.Moderate to strong winds associated with the new snow formed reactive wind slabs on leeward slopes at upper elevations. The middle and lower portions of the snowpack are 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.