Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Regions
South Columbia.
Conditions are tricky with an increasing load over multiple weak layers in the snowpack. Take a conservative approach to your terrain choices. If you see more than 30cm of new snow, consider the danger to be HIGH.
Confidence
Moderate - Intensity of incoming weather systems is uncertain
Weather Forecast
Sunday: 10-15 cm snow. Moderate south-westerly winds. Alpine temperature near -6.Monday: 20-30 cm snow. Moderate to strong south-westerly winds. Alpine temperature warming to near -2. Freezing level 1700m.Tuesday: 10-15 cm snow. Moderate south-easterly winds. Alpine temperature near -10. More information can be found in the Mountain Weather Forecast.
Avalanche Summary
On Saturday we received preliminary reports of a human-triggered Size 2.5 avalanche in Glacier National park, on a south east aspect near 2400m. Also on Saturday we received reports of heavy snowfall in the Monashees with 30 cm accumulating in 5 hours! A widespread natural avalanche cycle occurred in these areas Saturday afternoon. Although the spike of avalanche activity from Wednesday has decreased, on Friday we still received reports of storm slabs to Size 2.5 running on northerly aspects above 1900m. Several persistent slabs to Size 3 were also reported on Friday, running naturally and also directly triggered by explosives (and showing good propagation).With incremental loading on Sunday, human triggering will remain likely and avalanches could be surprisingly large due to the structure of the snowpack.
Snowpack Summary
Some areas in the Monashees received significantly more snow (30cm +) than was forecast on Saturday, resulting in a widespread natural avalanche cycle in the afternoon. Elsewhere in the region, 70 to 100 cm of storm snow sits on a layer of crust and/or surface hoar from mid-January. The crust is widespread, with the possible exception of high elevation north aspects. The recent storm snow fell with strong south winds, producing wind slabs in lee features at treeline and alpine elevations and in open areas below treeline.Deeper in the snowpack, the early-January persistent weak layer is buried 70 to 110 cm deep. Recent snowpack tests have shown sudden fracture characters with moderate loads and high propagation potential, as well as other signs of instability such as whumpfs, cracking and avalanches. Yet another persistent weak layer buried mid-December is 100 to 150 cm deep and consists of a facet/surface hoar/crust combination. It is most problematic at and below tree line.A rain crust buried in November is 150 to 200 cm deep. While generally considered dormant, occasional activity has shown that it may react where it is less deeply buried.
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.