Avalanche Forecast

Moderate - Uncertainty is due to whether buried persistent weak layers become active, triggering avalanches, with the arrival of the forecast weather.

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.

• Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
• Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
• Use small low consequence slopes to test the bond of the new snow.