Large destructive avalanches are very likely in northern parts of the region on Friday.
A problematic weak layer is buried 50-90 cm deep in the north of the region. The new snow will stress this layer and potentially produce very large avalanches that run far distances. This problem is largely absent in the south of the region.
Heavy snowfall and strong wind will create thick unstable storm slabs. Greater accumulations are expected in northern parts of the region.
THURSDAY NIGHT: 10-20 cm of snow by the early morning, freezing level rises with rain up to 1300 m, strong wind from the southwest, alpine temperatures increase to -2 C.
FRIDAY: Heavy snowfall throughout the morning with 10-25 cm by noon in northern parts of the region (24 hour totals of 30-50 cm) and 5-15 cm by noon in southern parts of the region (24 hour totals of 15-30 cm), slight clearing in the afternoon, strong wind from the southwest, freezing level will remain steady throughout the day with rain up to 1300 m and alpine temperatures around -2 C.
SATURDAY: A second storm starts Friday evening bringing another 20-40 cm of snow by Saturday afternoon, clearing in the afternoon, moderate wind from the southwest, freezing level drops to 800 m with alpine high temperatures around -5 C.
SUNDAY: Another weaker storm brings 5-15 cm of snow, moderate wind from the south, alpine high temperatures around -3 C.
Widespread avalanche activity is expected in northern parts of the region on Friday (e.g. Duffey, Hurley) as the storm will be more intense there and the snowpack structure is much weaker. Southern parts of the region will also have a storm slab problem, but the avalanches will likely be smaller.
On Wednesday, several large (size 2) natural avalanches were reported throughout the region. In the northern parts of the region, storm slabs were reactive to human triggering as 20-30 cm of snow sat above a weak layer of surface hoar. In the widespread avalanche cycle a week ago, avalanches in northern parts of the region were observed running to valley-bottom and failing on deeply buried weak layers. See this MIN report of an avalanche involvement from last week for an example of this avalanche problem.
A barrage of intense storms will continue to cause a widespread storm slab problem. Northern parts of the region will see 30-50 cm of snow between Thursday night and midday Friday while southern parts will only receive 15-30 cm. The previous storm deposited 20-30 cm of snow above a layer of surface hoar on New Year's Day, which resulted in reactive storm slabs.The snowpack below varies significantly between the northern and southern parts of the region. In the north (e.g. Duffey, Hurley), the upper snowpack consists of around 50-90 cm of snow that overlies a weak layer from late November composed of sugary faceted grains and hard melt-freeze crust. This presents a persistent slab problem that may remain problematic for weeks to months with the potential to produce large and destructive avalanches. This persistent weak layer is largely absent in the south of the region.
