Regions
Northwest Inland.
Flurries on Tuesday with SW winds may produce wind slabs on lee slopes. If more snow than forecast arrives, use caution at treeline and above.
Confidence
Fair - Due to the number and quality of field observations
Weather Forecast
An upper level trough will move into the area from the Pacific early Tuesday bringing light precipitation, with perhaps 5 to 10 cm of new snow at upper elevations. A bit of clearing on Wednesday, then more light precip. on Thursday and Friday. Winds from the S-SW.Freezing levels should remain around 500m but may spike to 2000m on Wednedsay.
Avalanche Summary
Reports from yesterday include several natural radiation triggered avalanches on steep solar aspects. No other reports of avalanche activity.
Snowpack Summary
Strong and variable winds have created soft and stiff wind slabs on varying aspects in exposed terrain. Below the recent storm snow is a rain crust at lower elevations and a temperature crust has formed in some locations from the recent temperature inversion. In the mid-pack a surface hoar layer has been reported, although it appears to be spotty in distribution. Near the bottom of the snowpack is a crust facet combo that was buried in mid-November.
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.