Storm slabs will likely be reactive on Thursday even with a brief lull in between storms. They may step down to deeper weak layers initiating large to very large avalanches.
Recent storm snow and strong southwest wind have built reactive storm slabs. Large avalanches are expected, especially where they sit above a crust buried in early December.
Weak faceted grains may overly a melt-freeze crust near the base of the snowpack. There is uncertainty on where this layer remains a problem in the region, but large avalanches have recently occurred in the northern half of the region. The most likely area to trigger it would be in thin, rocky snowpack areas.
By Wednesday morning the region received 25-35 cm of new storm snow with strong southwest wind. Expect reactive storm slabs particularly in wind-affected terrain at and above treeline. The snow will fall onto previous wind-affected snow at higher elevations, potentially a layer of surface hoar in sheltered areas, and a crust at lower elevations. Initially, the new storm snow will likely have a poor bond to these old snow surfaces.
The early-December crust is now down 100 cm in the alpine but close to the surface at and below treeline elevations. The early-November crust is buried around 100 to 200 cm at treeline elevations. The early-November crust may have weak and sugary faceted grains above it in parts of the region, which have produced large, full-depth avalanches in the past weeks. Uncertainty remains about where this layer remains a problem in the region, but it may be localized to the northern half of the region.
A small break in the series of storms on Thursday before the next system arrives for the weekend.
Thursday: Snow amounts 10 cm. Alpine temperatures near -2 with the freezing level 700 m. Ridgetop wind 30-50 KM/hr.
Friday: Snow 15-25 cm accompanied by 35-75 km/hr southwest wind. Freezing level 800 m.
Saturday: Snow 20-30 cm and rising freezing levels to 1100 m. Ridgetop wind 25-80 km/hr from the southwest.
On Wednesday, On Tuesday a few small cornice failures were reported and an explosive triggered storm slab up to size 2.
On Monday, a few naturally-triggered Icefall events up to size 2 were reported from Bear Pass. Loose-dry sluffing up to size 1 was seen from steep and rocky terrain features. The last deep persistent slab avalanches released on December 11 in the north of the region near Ningunsaw.
Data in this region is very sparse. Please consider sharing your observations with the Mountain Information Network; even just a photo of your day helps. Thank you to those that have already submitted this winter.
