Avalanche Forecast

Moderate - Uncertainty is due to extremely variable snowpack conditions reported through the region.

Monday night: Snowfall tapering, around 5 cm. Moderate SW wind switching NW. Treeline temperature around -5 °C. Freezing level dropping to valley bottom.

Tuesday: A mix of sun and cloud. Light NW wind. Treeline high around -7 °C. Freezing level valley bottom.

Wednesday: Mainly sunny. Light variable wind. Treeline high around -8 °C. Freezing level valley bottom.

Thursday: Snowfall 5-15 cm. Moderate SW wind. Treeline high around -5 °C. Freezing level 800 m.

On Monday in neighboring Glacier National Park, storm slabs were reactive naturally to size 3 at elevations below 1900 m, where they are suspected to have run on a recently buried layer of surface hoar. Many of these avalanches ran to valley bottom. Preliminary observations within the region from the storm Sunday/Monday include a natural cycle size 1.5-2.

A warm storm on Wednesday and Thursday last week triggered a widespread natural avalanche cycle up to size 3.5 (very large) at upper elevations. 

The large loads applied to the snowpack during these storm cycles, in combination with warm temperatures has enough to trigger the deeply buried December layer, producing numerous very large avalanches. As of Monday, observations continue to roll in from throughout the region of deep persistent slab avalanches. These avalanches are generally around 2100 m, size 2.5-3.5 (very large), 100-150 cm deep and on NE-NW aspects.

20-30 cm of new snow has likely been redistributed into leeward terrain features at upper elevations. A few concerning layers can be found in the upper snowpack. We have uncertainty about if/when these layers will become active (or if they have been during the most recent storm) so we will continue to track them. Most notably:

• A shallowly buried thin, breakable crust as high as 1800 m in the Selkirks and into the alpine in the Monashees.
• A reactive layer of surface hoar buried 40-80 cm deep in sheltered areas treeline and below. In neighboring Glacier National Park, large, low elevation avalanches running during the day Monday were attributed to this layer.
• A layer of facets or surface hoar from the cold snap in early January may be found down 70-100 cm but has not been reactive recently.

The early December crust/facet interface is now typically down 80-140 cm, but as deep as 200 cm in wind loaded terrain. It consists of faceted grains above a decomposing crust formed by the Atmospheric River rain event at the end of November. There has been avalanche activity on this layer as recently as recently as Friday in the region. Heavy triggers like natural cornice falls and storm slab avalanches may still have potential to step down to this layer resulting in very large avalanches.

• Continue to make conservative terrain choices while the storm snow settles and stabilizes.
• Be carefull around freshly wind loaded features.
• Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
• Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.