Regions
Northwest Inland.
New snow and strong wind Wednesday night and Thursday will create storm slabs at upper elevations. Be especially wary of wind-loaded, leeward and cross loaded slopes.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
TONIGHT: Flurries. Accumulation 5-10 cm. Ridge wind strong to extreme, southeast. Temperature near -8. Freezing level valley bottom.THURSDAY: Cloudy, Flurries. Accumulation 5-10 cm. Ridge wind strong, east. Temperature near -10. Freezing level valley bottom.FRIDAY: Mix of sun and cloud. Ridge wind moderate, east. Temperature near -14. Freezing level valley bottom. SATURDAY: Sunny. Ridge wind light, east. Temperature near -10. Freezing level valley bottom. Alpine inversion.
Avalanche Summary
Tuesday there were reports from northern parts of the region of loose dry storm snow releases up to size 1.5 in steep terrain as well as a skier triggered storm slab (size 1) on steep, southeast-facing, roll that failed on a buried sun crust.On Monday there was a report of a natural size 2 storm slab release on a east aspect below treeline feature that failed on facets buried by recent storm snow. Skiers also reported triggering small storm slab releases on steep convex rolls below treeline.With continued moderate to strong westerly winds it's likely that recent snow and wind loading at treeline and alpine elevations has primed conditions for human-triggering or natural avalanches.
Snowpack Summary
Light snow and strong winds continue to create wind slabs in open terrain at alpine and treeline elevations. These cover old hard wind slabs and scoured surfaces in many exposed areas. In wind-sheltered terrain, sun crusts or dry facets sit below the recent storm snow.Around 50-150 cm down, you will find a crust/surface hoar layer from mid-January, which still has the chance to surprise you and could be triggered from a thin snowpack spot, or with a large trigger like cornice fall.Facets at the base of the snowpack could possibly be triggered from shallow snowpack areas.
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.