Recent snow and wind are likely to form reactive slabs. Avoid drifted areas and assess open slopes and rollovers where a weak layer may be preserved.
10-20 cm of recent snow and variable winds have created wind slabs on lee features at upper elevations. Given the shift in wind direction, wind slabs should be expected in leeward features across a wide range of aspects.
A weak layer of surface hoar buried Jan 11 can be found 40-60 cm deep. There is uncertainty with how this persistent slab problem will react to the load from the new snow and wind. A couple of surface hoar layers from December can still be found buried 70-120 cm and 110-190 cm below the surface. They are highly variable in distribution and trending toward dormancy, but the possibility exists for avalanches to step down to these layers.
Sunday night: Cloudy, continuing flurries bringing up to 5 cm of snow, moderate northwest winds, freezing level dropping to valley bottom.
Monday: Mix of sun and cloud, light northwest winds, alpine high temperatures near -8 C.
Tuesday: Increasing cloud, scattered flurries moving in overnight with up to 5 cm of accumulation, winds shift to the southwest and increase to strong, alpine high temperatures around -7 C.
Wednesday: Mix of sun and cloud, light northwest winds, alpine high temperatures near -13 C.
Recent snow and wind have added a new storm slab problem, while also adding more load to the Jan 11 buried surface hoar. On Sunday, operators in neighboring Glacier National Park reported a large (size 2) wind slab releasing naturally in the storm snow on a north aspect.
There is uncertainty as to how a weak layer of surface hoar buried Jan 11th will react to the recent snow and wind. In the south of the region, operators were able to initiate small (size 1) avalanches breaking on the surface hoar 30-40 cm with ski cuts.
An extensive natural avalanche cycle occurred during last week's storm as up to 70 cm of new snow blanketed the region and was subsequently redistributed by strong winds. Several of these avalanches were thought to have stepped down to deeper layers (see this MIN reports from Mt. MacPherson for an example). Avalanches breaking in the recent storm snow have the potential to step down to deeper layers, creating larger and more destructive avalanches.
Snow accumulations over the weekend ranged from 10-30 cm, with higher totals in the Monashees. Moderate winds have varied in direction, gradually switching from the southwest to the northwest. This has the potential to create a tricky wind-loading pattern at upper elevations.
50-70 cm of snow from the past week has buried a weak of layer of surface hoar that continues to show reactivity in snowpack tests. This persistent weak layer is more likely to be preserved at elevations above where a thick crust exists and below more wind-affected terrain. It is most suspect in sheltered, open slopes at and below treeline.
A couple of older persistent weak layers exist in the mid to lower snowpack. The distribution of these layers is variable, but they follow a similar pattern to the layer discussed above. The upper layer from late December, down about 70-120 cm, consists of spotty surface hoar at shaded treeline and below treeline elevations. The lower layer from early December buried 120-190 cm deep consists of a combination of decomposing surface hoar with a crust and faceted snow. Snowpack tests on these layers show increasingly resistant results. The lower layer is now largely unreactive, but remains a prominent snowpack feature.
