Regions
Northwest Inland.
It won't take much new snow, wind, or warming to tip the balance and activate the lurking persistent weakness in the snowpack. Cautious decision-making is crucial.
Confidence
Moderate - Intensity of incoming weather systems is uncertain on Friday
Weather Forecast
WEDNESDAY: Cloudy with light snow – 3-5 cm. The freezing level is at valley bottom and winds are moderate from the S-SE. THURSDAY: Cloudy with light snow. The freezing level could rise to 1000-1200 m. Winds also rise to strong from the SE-SW. FRIDAY: Moderate precipitation starting Thursday evening with 10-20cm of total accumulation and freezing levels as high as 1000m.
Avalanche Summary
Reports from Monday include extensive natural loose dry sluffing up to Size 1.5 in steep terrain, and one relatively harmless stubborn .skier controlled wind slab avalanche in a heavily wind-loaded pocket at the top of a terrain break. On Saturday, there was one report of an intentionally skier triggered size 2 slab avalanche in the Ashman area. This slide may have released on the buried mid-Jan surface hoar layer, down around 50 cm in this area. There was also a report of a size 2.5 slab that was remotely triggered from the far SW corner of the region on Sunday. This slide initiated on the mid-Jan layer and likely stepped down to the Boxing Day surface hoar layer.
Snowpack Summary
Generally 5-20 cm of new snow has accumulated this week. At higher elevations this snow may be covering previously wind affected snow or settled old snow. Below 1200-1400 m the new snow probably sits on a crust. Fresh soft wind slabs are likely in exposed lee terrain. The early or mid January surface hoar layer is reported throughout the region and is generally 30-50 cm deep. Observers have found this persistent weakness on all aspects and at all elevations. It consistently produces moderate "pops" results in snowpack tests. Below this, the Boxing Day surface hoar problem may also be lurking. The mid and lower snowpack is generally quite weak and faceted, especially in lower snowpack areas.
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.