Regions
Northwest Coastal.
Avalanche danger will rise on Tuesday due to rapidly rising temperatures and the presence of a significant buried persistent weak layer. Stick to low angle terrain that is not exposed to overhead avalanche paths.
Weather Forecast
Tuesday: Mainly sunny. A strong alpine temperature inversion is likely between 1500 and 2300 m. Treeline temperatures should be near +5. Temps may remain cooler further inland. Outflow winds should ease off during the day. Wednesday: A mix of sun and cloud. The freezing level on the coast remains near 2300 m and near surface inland. Winds are light and variable.Thursday: A mix of sun and cloud with a chance of precipitation near the coast. The freezing level on the coast remains near 2000 m and near surface inland. Winds are light and variable.
Avalanche Summary
Numerous natural and skier triggered wind slabs up to size 2 were reported on Sunday in response to the outflow winds. A few large remotely triggered slab avalanches were reported in the Shames backcountry on Saturday. These were primarily from open alpine and treeline terrain and probably released on the February persistent weakness. In addition, a size 2.5 accidentally triggered slab avalanche was reported in the northern part of the region on saturday. This slide released on basal facets in steep rocky alpine terrain.
Snowpack Summary
Strong N-SE outflow winds have resulted in reverse loading and cross loading in exposed terrain at all elevations, and have scoured exposed windward slopes. The prominent mid February persistent weakness (surface hoar, facets, crust and/or wind pressed surfaces) is down 60-100 cm in the north and 120-160 cm in the south. Snowpack tests are now giving moderate to hard "pops or drops" shears on this weakness, and several whumpfs are still being reported. Basal facets and/or depth hoar remain a concern in shallow snowpack areas in the northern part of the region. Cornices are also large and may become weak if northerly winds start to undercut them.
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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.