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 5-10 cm of new snow in the alpine combined with strong winds overnight. Snow and strong wind continuing on Thursday with 10-20 cm forecast during the day. Freezing levels dropping down below 1000 metres on Friday as winds decrease to light southerly and periods of light snow continue. Light winds and freezing level near valley bottoms on Saturday with flurries or light snow.
Avalanche Summary
No new natural avalanches were reported on Tuesday. Some small avalanches up to size 1.5 were reported to be remotely or accidentally triggered on Tuesday. Natural avalanches up to size 3.0 were reported on Monday in the southern Monashees, and up to size 2.5 in the southern Selkirks. Numerous slab avalanches up to size 3 were reported over the weekend. Most of the natural avalanche activity occurred on Friday and Saturday but several were still reported on Sunday.
Snowpack Summary
Wind slabs continue to develop in the alpine and at treeline. In some areas these new wind slabs may be sitting on a layer of surface hoar. In other areas wind probably destroyed the surface hoar, or freezing drizzle created a thin crust at the beginning of the storm. I have continued to call the avalanche problem a wind slab, due to the widespread nature of the strong southwest winds. A thin new storm slab may exist in some areas in the south of the region. The persistent weak layer that was buried in early January is now down about 50-100 cm. This thick persistent slab overlies a variety of surfaces including large surface hoar, sun crusts, rime crusts and facets. The slab is ripe for human and natural triggers and is especially touchy at and below treeline. Rising freezing levels may increase the likelihood of triggering the persistent slab in the short term.
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.