Public reports of new wind slab avalanches at treeline coincide with Visitor Safety field work today which found touchy new windslabs in crossloaded terrain. Use caution as you transition into wind affected areas.
Weather Forecast
5cm of snow arriving for the Icefields Parkway with freezing levels rising to1800m on Wednesday. Alpine high of -6C tomorrow with flurries and SW winds, 20km/hr gusting to 50km/hr. Another pulse arriving Thursday bringing 5-10cm, high winds and freezing levels to 2000m.
Snowpack Summary
5-10cm of snow in past 72 hours being distributed by mod-strong SW winds. New wind slab forming in areas where snow available for transport. Solar aspects have a breakable crust 10cm thick. Mid-pack consists of buried wind and persistent slab, which lay on a bed of basal facets. Decomposing surface hoar ~40cm down in isolated areas at treeline.
Avalanche Summary
Field team in the Whistler Creek drainage reported isolated large avalanches to size 3 in the alpine from past 72 hours and remotely triggered 2 small avalanches in wind loaded terrain at treeline. These small avalanches are noteworthy because of the remote triggering, the significant propagation and slab thickness that ranged from 20cm to 1m.
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.
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.