Regions
Northwest Coastal.
Weather Forecast
20cm of new snow is expected by Wednesday morning with continued flurries, moderate winds, and rising freezing levels throughout the day. A warm front should move in from the Pacific on Wednesday night bringing strong southerly winds, freezing levels as high as 1000m, and heavy precipitation with up to 60mm by Thursday evening. Expect a brief reprise Friday morning, before the associated old front moves down from the north Friday midday with continued snowfall, strong southwesterly winds and freezing levels back down to valley bottoms.
Avalanche Summary
There was very little avalanche activity reported on Monday, despite the strong solar radiation. Recent reports include several natural wind slab avalanches up to Size 2 on north through northeast aspects near ridge crests, with one Size 2.5 on a cross-loaded west aspect. Natural loose snow avalanches up to Size 1.5 were also observed in steep and confined terrain but they ran far.
Snowpack Summary
Strong westerly winds are keeping wind slabs fresh and weak on lee aspects and isolated afternoon down flow (katabatic) winds were reported to have deposited new wind slabs primarily in gully features and on northerly aspects. The early February persistent weak layers seem to be bonding, but remain a concern at higher elevations with heavy triggers such as cornice falls. While below treeline persistent slabs are reactive to human triggers on isolated sheltered steep terrain where buried surface hoar is preserved. Surface hoar buried at the beginning of March remains unreactive due to limited slab formation.
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.