One more day of cool weather until rising temperatures elevate the danger.
Confidence
Moderate - Freezing levels are uncertain on Tuesday
Weather Forecast
MONDAY: Cloudy, moderate winds increasing to strong throughout the day, alpine temperatures around -6 and rising overnight.TUESDAY: Scattered flurries with up to 5 cm of new snow, extreme southwest winds, freezing levels around 1600 m and possibly higher on the eastern slopes.WEDNESDAY: Scattered flurries with up to 5 cm of new snow, strong southwest winds, freezing levels around 1800 m and possibly higher on the eastern slopes.
Avalanche Summary
No new avalanche reports from the weekend. An MIN report from Waterton Park on Friday shows a large size 3 deep persistent slab avalanche triggered by a smaller wind slab on a feature with highly variable snow depths. Although an isolated event, this avalanche highlights the possible consequence of our tricky persistent slab problem, especially with the incoming change of weather.
Snowpack Summary
Up to 20 cm of recent snow has buried a variety of old snow surfaces. These consist of heavily wind scoured areas and old wind slabs, surface hoar in sheltered areas, and widespread faceted (sugary) old snow. Recent moderate winds from a variety of directions have redistributed some of this new snow on leeward slopes, forming reactive wind slabs.The mid pack appears to be quite variable throughout the region and the structure is dependent on snow depth. In deeper snowpack areas, the snowpack appears to be well settled and right side up with isolated concerns for the mid-December weak layer found 50 to 80 cm deep. In shallow snowpack areas and lower elevations, the snowpack is heavily faceted and there are concerns for the mid-December weak facet layer as well as weak basal facets. If a persistent slab is triggered from thinner snowpack areas it may release on the basal facets resulting in a full depth avalanche. At this point it seems like a low probability, high consequence scenario. However; once the snowpack starts to see a big change, like warming, the likelihood of triggering may increase.
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.