Regions
Northwest Inland.
Snow is finally on the horizon! We're expecting a rapid change from cold and dry to moist and mild on Friday. This sudden change could be enough to wake up the mid February weak layer and produce large avalanches.
Confidence
Fair - Forecast snowfall amounts are uncertain
Weather Forecast
Thursday: Cloudy with sunny breaks and a chance of flurries. The freezing level is at the surface. Ridge winds are light to moderate from the S-SW. Friday: Moderate snowfall – 10-20 cm. The freezing level climbs to 800 m in the south and remains near valley bottom in the north. Winds are strong from the S-SW. Saturday: Light to moderate precipitation. The freezing level is between 1000 and 1500 m. Winds are moderate to strong from the SW.
Avalanche Summary
No new avalanche activity reported. Expect this to change on Friday with forecast snowfall, warming and strong winds.
Snowpack Summary
Persistent cold dry weather has resulted in significant new surface hoar growth and surface facetting on shady slopes at all elevations. Steep solar aspects may have a sun crust. The early February weak layer of facets, crusts, and surface hoar is buried down about 35-80 cm. The snow above the crust has been transported by Southwest winds and then reverse loaded by Easterly or Southeast winds. Cold temperatures have not settled the snow above the weak layer into a cohesive slab, and the cold has preserved the weak layer and associated crusts. I suspect that there will not be much change or improvement in the bonding of the late February snow to the crusts and facets. Snow pack tests may help to show when this layer demonstrates more resistance to added forces.
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.