New snow amounts will vary throughout the region on Saturday. Danger will be HIGH in areas that receive more than 20 cm of new snow.
New snow, wind loading, and warming will stress weak layers of surface hoar buried 40-100 cm deep. Storm slab avalanches may step down to these layers and produce large avalanches with wide propagation across terrain features.
Fresh storm slabs will build throughout the day. Natural and human triggered avalanches are likely in areas that receive more than 20 cm of snow and on alpine slopes that are being loaded by the wind.
FRIDAY NIGHT: Storm arrives with 5-25 cm of snow by the morning, 80-120 km/h wind from the southwest, freezing level climbing to 1000 m.
SATURDAY: Snow continues throughout the day with another 10-25 cm of snow above 700 m, 80-100 km/h wind from the southwest, freezing level around 1000 m and alpine high temperatures around -1 C.
SUNDAY: Scattered flurries with 5-15 cm of snow, 30-40 km/h wind from the south, alpine high temperatures around -1 C.
MONDAY: Next frontal system arrives bringing 20-30 cm of snow by the afternoon, 60-90 km/h wind from the southwest, freezing level around 1000 m.
Natural avalanches are expected in parts of the region that receive more than 20 cm of new snow on Saturday. Human triggering will also be very likely on freshly loaded slopes. There is additional concern about the buried surface hoar layers, as the combination of new snow, wind loading, and warming could increase the likelihood of large persistent slab avalanches on these layers.
Over the past week there have been ongoing reports of size 1-2 wind slab and storm slab avalanches (both natural and explosive triggered), but there are no reports of larger persistent slab avalanches. If Saturday's storm doesn't result in a persistent slab avalanche activity, then Monday and Tuesday's more intense storm likely will.
Saturday's storm will bring 15-50 cm of snow to the region with very strong wind and warming temperatures. Expect fresh and reactive storm slabs and wind slabs to form in certain parts of the region. This could also be the extra load needed to wake up one of two buried layers of surface hoar between 40-100 cm deep. These layers were buried a few weeks ago and have been reactive in snowpack tests. Reports from the Shames area suggest buried surface hoar can be found on all aspects, but is more prevalent on southeast to southwest aspects around 800-1400 m, as well as sheltered alpine areas. The lower snowpack is generally considered strong.
