Regions
Northwest Inland.
Pay close attention to new snow amounts and whether or not the surface snow is loose or cohesive. Tricky conditions are likely if a cohesive slab forms.
Confidence
Low - Due to the number of field observations
Weather Forecast
Friday: Cloudy with up to 5 cm of new snow. The freezing level is at valley bottom and winds are moderate from the SW. Saturday: Mainly cloudy with sunny breaks and a chance of flurries. The freezing level is at valley bottom and winds ease to light. Sunday: Mainly cloudy with a chance of flurries. The freezing level is at valley bottom and winds are moderate from the southeast.
Avalanche Summary
There is a new report of two skier controlled size 2 slab avalanches from the Ashman area on Tuesday. These failed on the Jan 5/Dec 26 surface hoar layers down 20-50 cm deep. On Monday, a small natural cornice release triggered a size 2.5 slab avalanche in the north of the region. Skiers also triggered a few slab avalanches size 1-2 in the north. All these avalanches released on the Jan 9 surface hoar layer down 30cm.
Snowpack Summary
An additional 5-10 cm of snow with moderate or strong southeast winds may be enough to form fresh, reactive wind slabs in lee features. In some places this could also activate buried surface hoar in the upper snowpack, generally found between 30 and 60 cm deep. 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. We have not heard of any full depth releases on weak basal layers yet.
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.