Regions
Northwest Coastal.
Increasing cloud and wind on Tuesday as a storm approaches the coast. Watch for reactive slabs in steep or wind loaded terrain.
Weather Forecast
TUESDAY: Overcast with snow starting midday and about 5 cm by the end of the afternoon, south wind increasing to 50-80 km/h, freezing level up to 1200 m.WEDNESDAY: 15-25 cm of new snow, strong south wind, freezing level around 1200 m.THURSDAY: Linger flurries with another 5-15 cm, moderate southwest wind, freezing level dropping to 700 m.
Avalanche Summary
On Sunday, a few recent natural storm slabs were reported (up to size 2), mostly sliding on 20-30 cm deep crusts. A few cornice falls and loose dry avalanches were reported as well. Recent storm snow may remain reactive to human triggers, especially as wind speeds increase on Tuesday.
Snowpack Summary
20-30 cm of recent storm snow is settling at higher elevations. Thick supportive crusts are forming overnight below 1300 m and deteriorating throughout the day with warming. The snow below treeline may become weak and release as loose wet avalanches in steep unsupported terrain features. The late February persistent weak layer continues to be a concern for triggering large avalanches. This combination of crust and weak facets is now down 100-150 cm, and may be triggered by light loads in shallow weak spots.
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.