Regions
Northwest Coastal.
The "Danger Ratings" are based on 20 cm or more snow for Sunday accompanied by strong winds. If you receive less snow, consider the rating to be one step to high.
Confidence
Fair - Forecast snowfall amounts are uncertain on Sunday
Weather Forecast
Sunday: A Pacific frontal system moves in bringing moderate to heavy precipitation amounts (25-40 mm). Ridgetop winds blowing strong from the SW. Alpine temperatures near -4.0 and freezing levels falling to 700 m. Monday: A trailing warm front moves onto the region bringing continued moisture and wind. Ridgetop winds will be strong from the South. Alpine temperatures -5.0 and freezing levels falling to 500 m. Tuesday: Unsettled conditions prevail with cloudy skies and no significant precipitation. Areas in the north may see some sunny periods. Ridgetop winds will be light from the South. Alpine temperatures near -7 and freezing levels will fall to 200 m.
Avalanche Summary
On Friday, several natural loose, slab and glide avalanches were spotted from a heli flight up to size 2.5. I suspect loose wet avalanches continued in below treeline elevations.
Snowpack Summary
New storm snow will blanket wind slabs (NE-W) that built over the past week. With strong winds from the SW, fresh wind slabs will form on lee slopes and behind terrain features like ribs and ridgelines. Lingering beneath (down 50-80 cm) sits a persistent weakness comprising of surface hoar, facets, and /or a crust. Recent test done on these layers are producing hard results with sudden and resistant planar characteristics. The mid pack is generally well settled and strong, although basal facets remain a concern in the northern part of the region.
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.