Regions
Kootenay Boundary.
The snow pack is complex and human-triggered avalanches are likely. Be extra cautious if temperatures begin to rise, or rain begins to fall at lower elevations as the next storm system approaches on Wednesday.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
TUESDAY NIGHT: Flurries. Accumulation trace. Ridge wind moderate, southwest. Temperature -5. Freezing level 800 m.WEDNESDAY: Cloudy, snow. Accumulation 10-20 cm. Ridge wind strong, south. Temperature near 0. Freezing level rising to 1800 m.THURSDAY: Cloudy, snow. Accumulation 5-10 cm. Ridge wind strong, southwest. Temperature near 0. Freezing level 1500 m.FRIDAY: Cloudy, flurries. Accumulation trace. Ridge wind light, southwest. Temperature -2. Freezing level 1000 m.
Avalanche Summary
On Monday there were reports of two successive skier accidentals triggered on a northwest aspect between 1980-2000 m. The first was a size 1.5 and the second about thirty minutes later was a size 2. A natural size 2 loose wet avalanche was also report on a soutwest aspect at 2100m, as well as numerous explosive triggered size 2-3.5 slab avalanches running on weak layers deep in the snowpack.Sunday there were reports of natural loose wet avalanches to size 2.5 on solar aspects as well a size 3 deep-persistent, slab avalanche on a northerly aspect that's suspected to have failed on the December 15th layer.Very significant avalanche activity occurred in the region last Wednesday and Thursday. A smaller avalanche cycle, mostly affecting the recent storm snow was reported on Saturday. As temperatures warm lower elevations that have so far remained cool during the inversion, there is still an increased likelihood of triggering something large.
Snowpack Summary
Warm alpine temperatures have formed a crust on solar aspects while northerly aspects still hold dry snow. Below the surface, 40 to 60 cm of recent snow has settled into a cohesive slab on top of the reactive January 5th interface which consists of a crust/surface hoar combination on steep southerly aspects and pure surface hoar on remaining aspects. The late December surface hoar layer also remains reactive and is now buried 80 to 90 cm below the surface. Adding to the complexity of the mid to upper snowpack is the mid-December surface hoar layer which is now 100 to 130 cm below the surface. This spooky interface continues to produce sudden snowpack test results and is most pronounced at treeline, but is also present below treeline. The overlying slab is now deep, dense and destructive. Two laminated crusts created by rain events in late November lay just below the mid-December interface, and may co-exist with facets. In shallow, rocky terrain the mid-December surface hoar and the late November crust seem to be reacting together which is a volatile combination.
Problems
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.
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.