Regions
Northwest Inland.
Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain on Thursday
Weather Forecast
10cm of new snow is expected by Wednesday morning with continued flurries, moderate winds, and rising freezing levels throughout the day. A Pacific warm front is expected to affect the region on Thursday bringing strong southwesterly winds, freezing levels as high as 1000m, and another 10-15cm by Thursday evening. The most intense snowfall is expected to happen overnight with another 15cm by Friday morning. Expect a brief reprise Friday morning, before the associated old front moves down from the north with continued snowfall, strong southwesterly winds and freezing levels back down to valley bottoms.
Avalanche Summary
Recent reports include evidence of a natural avalanche cycle that occurred during intense wind-loading on Sunday afternoon. This includes numerous natural cornice triggered slab avalanches up to Size 3, but mostly in the Size 1-2 range, as well as several Size 2 thin wind slabs. Slope cutting on Monday produced a Size 1-2 storm slab avalanche that failed on an old interface from late February.
Snowpack Summary
Alpine and treeline areas are generally less wind affected than expected given the recent intense winds, but fresh weak wind slabs are lurking in many areas. Recent snowpack tests on a northeast aspect at 1480m gave several resistant planar shears the recent storm snow and two hard resistant planar shears down 37cm and 70cm where the total snowpack depth was 5m. The mid February interface, down around 60cm, is variable and generally consists of a strong melt freeze crust below 1000m. Above that elevation, expect to find buried facets, and/or surface hoar (in more sheltered areas), and/or a sun crust on southern aspects. The surface hoar is not widespread but is responsible for much of the larger avalanches that occurred earlier this week. This layer should be on your radar, as it may be susceptible to rider triggers.
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.