We welcome your observations. Click on "submit" to let us know what you are seeing out there.
Confidence
Fair - Intensity of incoming weather systems is uncertain
Weather Forecast
Temperatures start cooling on Saturday with the passage of a cold front. 10-15 mm precipitation is expected with the front overnight Friday/ Saturday, tapering to flurries on Sunday. The freezing level falls to around 1500 m on Saturday. Monday is dry and cool, with a chance of sun. Winds are moderate NW, easing to light by late Sunday.
Avalanche Summary
Size 1.5 wind slabs and a size 2.5 storm slab were triggered naturally on Thursday. A number of cornice collapses have been reported over the last few days. Loose wet avalanches failed naturally in steep terrain on Wednesday in response to warming. Also on Wednesday, explosives triggered a couple of size 2 slabs, which failed on the late-Jan crust. Human-triggering of the persistent slab remains possible.
Snowpack Summary
New snow may have been shifted into wind slabs on lee features at alpine and treeline elevations. Keep your eyes open for cornices, which may be large and unstable. A week or so of very warm temperatures has affected the snowpack, creating moist surface layers up to around 2000m. At low elevations, the snowpack may now be relatively uniform. The late-Jan crust/surface hoar layer, buried around a metre deep, remains a key concern, as it could still be human-triggered and could produce a destructive avalanche. The mid-January surface hoar is typically down 80-120cm and is unlikely to be triggered, apart from in a thin or rocky snowpack area. The mid-December weak layer is down over 120cm, but has been generally unreactive lately. Basal weaknesses remain in the back of operators' minds.
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.