New snow and southerly winds will be driving avalanche danger on Tuesday. Avoid exposure to avalanche terrain during periods of rapid loading by rain, snow, or wind.
Confidence
Low - Due to the number of field observations
Weather Forecast
The next system arrives on Tuesday with modest accumulations of snow and more seasonal temperatures. TUESDAY: Snow (5-15cm) during the day with another 5-10cm possible overnight. Moderate southerly ridgetop winds. Freezing level around 1000 m. Alpine temperatures near -5 Celsius.WEDNESDAY: Clearing throughout the day. Moderate westerly ridgetop winds. Freezing level around 1200 m. THURSDAY: Cloudy with isolated flurries. Light to moderate southwesterly ridgetop winds. Freezing level around 1100 m.
Avalanche Summary
No new avalanches were reported in this region. A natural avalanche cycle is expected on Tuesday, especially where new snow may be falling on a crust formed November 27th. We currently have very limited observations in this region. Please submit your observations to the Mountain Information Network (MIN).
Snowpack Summary
Warmer temperatures on Sunday may have resulted in a crust (November 27th crust) up to treeline elevations, with up to 10cm of snow on top of this crust. At higher elevations, southerly winds (gusting strong at times) likely re-distributed the new snow, forming wind slabs on lee features, such as below ridgetops and in gullies. Lower down in the snowpack,10-25 cm snow from last weekend sits on the previous warm temperature crust from November 23rd. We haven't had much information on how well the snow is bonding to this crust.The depth of the snowpack varies greatly with elevation. Recent reports suggest the average depth is 200+cm in the alpine, 100-160cm at treeline, and decreasing rapidly below treeline where the primary hazards are rocks, stumps, and open creeks. A major feature in the snowpack is a crust which was formed around November 11th and can be found approximately 100cm down at treeline elevations. We currently have very limited snowpack observations within this region and it is critical to supplement this information with your own observations.
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.