Avalanche danger will escalate throughout the day as heavy snowfall and warming temperatures weaken the snowpack.
New snow and warming will stress 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.
Up to 40 cm of new snow by Monday afternoon will result in a cycle of natural storm slab avalanches. Human triggered storm slabs will be very likely as snow accumulates.
SUNDAY NIGHT: Light flurries start overnight as strong frontal system arrives, wind increasing from moderate to strong from the southwest, alpine temperatures around -2 C.
MONDAY: Frontal system intensifies throughout the day with 15-40 cm of snow by the afternoon as snow level rises from 600 to 1000 m, strong to extreme wind form the southwest, alpine temperatures reach 0 C.
TUESDAY: Storm continues Monday night with another 20-30 mm of precipitation with rain up to 1200 m by the morning then cloudy in the afternoon, moderate wind from the southwest, freezing level around 1300 m.
WEDNESDAY: Scattered flurries with 5-15 cm of snow, light wind with moderate gusts from the west, freezing level drops to 500 m with alpine high temperatures around -2 C.
The incoming storm will result in natural avalanche activity. Since the storm is expected to hit peak intensity on Monday evening, the most dangerous conditions will be late afternoon and into the evening. The transition from snow to rain could cause a mix of avalanche problems later in the day including storm slabs, wind slabs, and wet loose avalanches on buried surface hoar layers.
Saturday's storm also resulted in natural avalanche activity, with numerous size 2 storm slab avalanches and several size 3 avalanches (on north and east aspects) that potentially ran on the buried surface hoar layers described in the persistent slab avalanche problem. The combination of new snow and warm temperatures on Monday and Tuesday will increase the likelihood of persistent slab avalanches.
The incoming storm will start cold delivering 15-40 cm of new snow by Monday afternoon before it starts raining up to 1200 m on Monday night. The new snow will add to the 15-50 cm of snow that fell Saturday, resulting in the potential for thick storm slab avalanches. Strong wind from the southwest will form formed extra thick unstable slabs 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.
