Regions
Northwest Inland.
Watch for fresh wind slab development on Tuesday.
Confidence
Low - Forecast snowfall amounts are uncertain on Wednesday
Weather Forecast
5-10cm of new snow and extreme southwest winds are expected on Tuesday. Trace amounts of new snow and moderate winds are forecast for Wednesday and Thursday. Freezing levels will hover around 1500m on Tuesday, drop to about 1000m on Wednesday and then rise back to 1400m by Thursday.
Avalanche Summary
There are very few recent observations from the region. A couple natural size 2 slab avalanches were observed in wind-loaded terrain (N-NE aspects) at around 1800 m on Friday. Light amounts of new snow and extreme southwest winds are likely to spark a new round of wind slab activity on Tuesday.
Snowpack Summary
Fresh and reactive wind slabs could be found in lee and cross-loaded features. There is a notable persistent weakness of buried surface hoar in many places, generally found between 30 and 60 cm deep. Wind, sunshine, and milder temperatures could help promote slab development in the snow overlying this interface. Stay tuned to signs of instability like recent avalanches, whumpfing, and shooting cracks. The mid pack that was reported to be well settled may have now facetted in the shallower areas, and the deeper basal layers are almost certainly facetted and weak.
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.