Avalanche danger below treeline may be LOW in the Cascades where the surface rain crust extends up to higher elevations.
Weather Forecast
Synopsis: A low pressure system will slide southeast and be replaced by a ridge of high pressure bringing more sunshine and mild temperatures for Thursday and Friday. Wednesday: Cloudy with a chance of flurries in the morning and sunny breaks in the afternoon. The freezing level is around 1200 m and winds are light from the southeast. Thursday: A mix of sun and cloud. The freezing level is steady around 1400 m and winds are light from the west-northwest. Friday: Mainly sunny. The freezing level should climb to 1600-1800 m during the day.
Avalanche Summary
Natural avalanche activity decreased on Sunday but there was one report of a size 2 skier triggered avalanche in the Duffey Lake area that resulted in injuries. Explosive control on the Duffey Lake road also produced several avalanches up to size 3 from northwest aspects. Most of these were suspected to have released on the late February surface hoar layer. There were no reports of new avalanches on Monday.
Snowpack Summary
Moderate ridge top winds have formed new wind slabs in exposed lee terrain. A dusting of new snow sits on 60-100 cm of settling storm snow or a rain crust below 1400 m in the north, and 1700 m in the south. Storm snow weaknesses have been gradually gaining strength over the past couple days. A weak layer of buried surface hoar (February 20th) and/or a crust sits at the base of the storm snow. This layer was the culprit in most of the large avalanches that occurred last weekend. Snowpack tests continue to show moderate "pops or drops" results and good potential for propagation. Triggering this layer is becoming more difficult, but I recommend avoiding any large slopes that did not release during the last cycle, especially when the sun pokes out later this week.
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.