Regions
Northwest Coastal.
A new storm is expected to add some load to the shallow weak early season snowpack. New storm slabs may be easy to trigger, and deeply buried weak layers may not support the added load.
Confidence
Fair - Forecast snowfall amounts are uncertain on Thursday
Weather Forecast
Overnight and Thursday: Models are showing about 20 mm of precipitation for near coastal areas by early morning. Strong South-Southwest winds are expected to reach 80 km/hr in the alpine. Light precipitation is forecast to continue on Thursday. Freezing level should be about 1500 metres at the beginning of the storm and slowly drop to 800 metres by Thursday afternoon.Friday: 5-10 mm of precipitation is forecast with continued strong Southwest winds and freezing levels rising to about 1200 metres during the day.Saturday: Very light precipitation combined with moderate Southwest winds that should change to light Northerly late in the day. Freezing level should drop to valley bottoms by Saturday evening.
Avalanche Summary
No new avalanches reported. Expect new storm slabs to develop during the storm. The added load of new snow and wind transported snow may overload the weak layer where the buried crust exists near the ground.
Snowpack Summary
Reports of extensive wind transport since the end of the November 23rd storm. There is a little more than a metre of snow at 1000 metres elevation, and the snowpack has been described as "generally moist" below this elevation. Snowpack tests resulted in moderate planar results down about 20 cm, and hard planar results on the early season crust down about 90 cm. These layers of concern may persist or become more reactive with the forecast snow load in the next few days. New storm slabs are expected to develop due to the forecast strong winds and new snow.
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.