Warm, Wet, and Windy storm will create new wind slabs and add load above the persistent weak layer. Conservative terrain use recommended at this time.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Freezing levels are uncertain overnight. Most products are suggesting that freezing levels will rise up to about 1700 metres, however there is a chance that freezing levels may rise as high as 2200 metres. This is more likely in the west of the region. Expect 5-8 cm of new snow in the alpine overnight combined with strong southerly winds. New snow and strong southerly winds are forecast to continue during the day on Thursday resulting in 10-15 cm. Freezing levels dropping Thursday night down to about 1000 metres by Friday morning. Light snow and light southerly winds on Friday. Light winds and flurries on Saturday combined with continued cooling.
Avalanche Summary
No new avalanches reported. One size 1.5 natural avalanche was reported on Monday. On Sunday, a skier remotely trigger a size 1 avalanche on a NW aspect from 10m away. The slab was 60cm thick which suggests that it failed on the early January surface hoar layer. Natural loose avalanches up to size 2 were also reported from extreme terrain and did not trigger any slabs below. Widespread natural avalanche activity up to size 3 was reported on Friday and Saturday.
Snowpack Summary
New wind slabs are developing in the alpine and at treeline. Wind slabs and recent storm slabs have added load and stress to the already volatile persistent slab. There are a couple of highly reactive layers of surface hoar typically down 70-100cm which have been responsible for numerous recent large avalanches. The persistent slab is ripe for human and natural triggers and is especially touchy at and below treeline. The mid and lower snowpack below these layers is generally well-settled and strong, with any old weak layers considered dormant for now. Snowpack depths are variable and shallow snowpack areas may have weak facetted crystals near the ground.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.