Regions
Northwest Inland.
We're expecting moderate snow and very strong upper winds over the next 24 hours. Areas that don't see much snow could see slightly lower avalanche danger on Monday.
Confidence
Poor - Due to the number of field observations
Weather Forecast
Tonight and Monday: Moderate snowfall 5-10 cm. The freezing level is generally around 500 m but an above freezing layer between 1000 and 1500 m is possible. Winds are moderate to strong from the SW. Tuesday: A mix of sun and cloud with a chance of flurries. The freezing level is near valley bottom and winds are light to moderate from the northwest. Wednesday: Another frontal system approaches the coast and could bring periods of snow later in the day. The freezing level is around 500-800 m.
Avalanche Summary
There are a couple reports of recent natural avalanche activity from the Ashman and Hankin areas. In Hankin a couple large slab avalanches (~size 2.5) were observed on northeast facing terrain near ridgetop. These likely released during previous storm and/or wind events and appeared to release near the base of the snowpack. In Ashman a couple smaller storm slabs were observed on steep convex rolls from south facing slopes.
Snowpack Summary
The past few days have brought around 60-70 cm of storm snow with steady strong W-SW winds and fluctuating freezing levels. The most recent storm snow came in with rising temperatures and is likely "upside down" feeling, meaning more dense on top. Expect touchy wind slabs in exposed lee terrain and cross-loaded features well into treeline. A number of rain crusts may exist in the upper and mid snowpack, primarily below 1500 m. Deeper in the snow pack a layer of facets/surface hoar formed in early December may be found in the top 100cm in the Ashman area. The mid and lower snowpack is still structurally weak and faceted. Depth hoar and an early season crust exist near the ground.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.