A significant storm is expected to impact this region starting Tuesday afternoon and overnight into Wednesday. Expect very dangerous avalanche conditions in this region through this period.
Confidence
Fair - Intensity of incoming weather is uncertain
Weather Forecast
Tuesday: A significant storm is expected to hit the region starting Tuesday around noon and ramping up during the afternoon and overnight. Expect around 15 cm new snow expected by the end of the day and another 15-20 overnight. Ridgetop winds gusting to 75 km/h from the southwest. Freezing level rising briefly to around 1500m late on Tuesday, but mostly staying around 800 m.Wednesday: Snowfall lingering until noon, then clearing. Temperatures falling rapidly. Winds diminishing.Thursday: Dry and cold. Temperatures around -8C. Winds becoming light northerly.
Avalanche Summary
Relatively small soft slab avalanches were easily triggered on Monday. With further loading by new snow, the potential for larger, more destructive avalanches will increase through Tuesday and Wednesday.
Snowpack Summary
The new snow is bonding poorly to existing snow surfaces that include surface hoar (up to 20 mm in size), facets, hard wind slabs or a sun crust. The upper storm slab has so far been reported as thin (20-30 cm) and soft. However, with more snow it will rapidly increase in thickness and danger. Recent SE winds have formed new wind slabs at alpine and treeline elevations. No significant shears have been observed recently below the recent storm snow in the mid snowpack layers. Near the base of the snowpack, a crust/facet layer exists, which is now unlikely to be triggered, except perhaps by heavy triggers in steep, shallow, rocky terrain where more facetting has taken place.
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.