Large storm slab avalanches are primed for human triggering. Stick to simple low-angle terrain.
New snow, wind loading, and warming has likely stressed weak layers of surface hoar buried 50-120 cm deep. Smaller avalanches may step down to these layers and produce large avalanches that propagate across entire terrain features.
20-50 cm of fresh snow and strong wind has formed widespread storm slabs. Human triggering is likely on steep, convex, and wind loaded slopes.
SATURDAY NIGHT: Scattered flurries with 5-10 cm of snow along the coast and up to 5 cm further inland, moderate wind from the southwest, alpine temperatures around -2 C.
SUNDAY: Scattered flurries with 5-10 cm of snow, light to moderate wind from the southwest, alpine high temperatures around -1 C.
MONDAY: Next frontal system arrives bringing 20-30 cm of snow by the afternoon, strong wind from the southwest, freezing level climbs to 1400 m.
TUESDAY: Stormy weather continues with another 25-40 cm of snow, strong wind from the southwest in the morning then easing to moderate in the afternoon, freezing level around 1400 m.
Preliminary reports suggest a cycle of natural storm slab avalanches occurred in some parts of the region on Saturday (these areas received at least 30 cm of storm snow). Human triggered storm slabs will remain likely on Sunday. There is additional concern about buried surface hoar layers, as the combination of new snow, wind loading, and warming has likely increased the stress on these layers. If Saturday's storm didn't already result in persistent slab avalanche activity, then Monday and Tuesday's more intense storm likely will.
Saturday's storm delivered 30-50 cm of snow to many parts of the region, with the exception of the Shames area that only received 15-20 cm. Strong wind from the southwest likely formed deeper deposits in lee terrain. This could be the extra load needed to wake up either of the two layers of surface hoar buried 50-120 cm deep. 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.
