I bumped the alpine danger up a notch to Considerable for Thursday due to forecast new snow and wind continuing to develop wind slabs over an easy sliding layer.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain on Thursday
Weather Forecast
Some moisture trapped in the south to north flow coming out of Washington State should bring 3-5 mm of precipitation (5-10 cm of snow at treeline) overnight, and another 3-5 mm of precipitation during the day on Thursday. Winds are expected to be light from the southeast and alpine temperatures should remain around -5. High pressure with light winds and cooler air should move into the region from the north on Friday. Some flurries may continue on Friday and Saturday with periods of broken skies and alpine temperatures around -10. The north of the region may be closer to -15 in the alpine by Saturday.
Avalanche Summary
Thin new windslabs were reported releasing up to size 1.0 in the north of the region. One third hand report of a remotely triggered size 2.0 wind slab on a North aspect at 2440 metres near Panorama.
Snowpack Summary
Light new snow falls have buried large surface hoar on all aspects at and below treeline and on shaded aspects in the alpine. Easterly winds associated with the new snow may have disturbed surface hoar in the alpine. New snow on southerly aspects may be sitting on a sun crust and/or surface hoar, providing an easy sliding layer. The new snow should be mostly unconsolidated except where it has been re-distributed by the wind. Fresh wind slabs may be sitting on 10-20 cm of facetted snow on all but steep solar exposed aspects. In the southern Purcells, (west of Kimberley), a prominent layer of buried surface hoar has shown to be reactive to human triggers. In this part of the region, it's buried down 40 cm with a cohesive slab above it. Shallow snowpack areas and moraine features may have weak facetted snow near the ground that will require time and some warming to strengthen.
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.