Persistent midpack weaknesses are more pronounced in the northern portion of the forecast zone, with human triggering more likely than the Icefields area.
Weather Forecast
Flurries are expected overnight but with little accumulation resulting as a cold arctic front starts to sweep SW from the icy NE. Clearing expected Sunday and into next week with sunshine and cold nights.
Snowpack Summary
Available snow has been redistributed by strong, variable direction winds. In sheltered Treeline locations, the weak midpack layers are reactive down 50cm. Where snow remains in the Alpine, new wind slabs are reactive to triggering from additional load or solar, and wind-stiffened snow at Treeline is transmitting collapses large distances.
Avalanche Summary
Isolated windslab avalanches were observed today in the Icefields area and loose dry avalanches to size 2 were observed in the Tonquin valley. East, South, and North aspects have formed windslabs and large cornices that have failed in the last 48 hrs in the north portion of the forecast zone.
Confidence
Due to the number of field observations
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.
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.