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 amounts of snow and more seasonal freezing levels. TUESDAY: Snow (5-15cm) during the day with another 5-10cm possible overnight. Moderate southerly ridgetop winds. Freezing level around 1000 m.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
On Monday, a Size 2 wind slab was reported with explosives control work in the north of the region on a northerly aspect near 2300m. Natural avalanche activity is expected on Tuesday with another pulse of snow. We currently have very limited observations in this region. Please submit your observations to the Mountain Information Network (MIN).
Snowpack Summary
Last week, the November 23rd crust formed as temperatures cooled and the rain-soaked snow surface froze. Since then, 15-40cm of snow has fallen at treeline and above with moderate to strong south (west) winds, creating wind slabs sitting on a crust. The depth of the snowpack varies greatly with elevation. Recent reports suggest the average depth is 150+cm in the alpine, 100-150cm at treeline, and decreasing rapidly below treeline where the primary hazards are rocks, stumps, and open creeks. There are two other layers of concern in the snowpack: 1) The Halloween crust (down 100cm at treeline elevations) and 2) The November 10th surface hoar / facets (down 80cm 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.