Avoid shallow rocky terrain where the snowpack transitions from thick to thin. Terrain features that fit that description at upper treeline and in the alpine are especially concerning. This is where riders are most likely to trigger a large destructive deep persistent slab avalanche.
Brief periods of sun could quickly initiate natural avalanche activity. Avoid exposure to avalanche terrain and overhead hazard when solar radiation is strong.
Variable winds have transported storm snow into wind slabs that can be found on all aspects at treeline and above. In areas where slopes are receiving direct solar radiation reactivity of wind slabs could increase rapidly.
Be aware that if triggered wind slab avalanches could step down to deeper layers.
Last week the weak layers from January and February produced human triggered avalanches at treeline and above on a variety of aspects. On shaded slopes, these layers will generally present as surface hoar, and on sun-exposed slopes they will generally present as facets and a crust.
Avalanches triggered on these layers can step down to the facets at the bottom of the snowpack resulting in a very large avalanche.
These layers can be remotely triggered. Avoid traveling below steep slopes.
The base of the snowpack remains very weak. Very large human triggered avalanches are possible at treeline and above. Avoid shallow and rocky areas, where the snowpack depth is highly variable. This is a very concerning avalanche problem and should stay in your mind when traveling in the backcountry.
Human triggered avalanches are likely to continue to occur in this region.
On Monday, a cornice trigged, size 3 avalanche was observed. The cornice triggered wind slabs below on a steep rock north-facing slope.
Through the weekend, natural and explosive triggered storm slab and deep persistent slab avalanches were reported to size 3. A skier remote size 3.5 deep persistent slab avalanches were reported near Golden. These avalanches all released around 2500 m and on easterly aspects. This MIN shows some large, naturally occurring deep persistent slab avalanches.
On Wednesday a fatal avalanche incident involving a group of skiers occurred in the Purcell Mountains west of Invermere BC. The size three avalanche was triggered on a southwest facing slope at 2500 m. The weak layer of facets buried in late November that sits at the bottom of the snowpack was responsible for this avalanche.
The Purcells are likely to continue to see very large destructive avalanches failing on the basal facets from late November. While we are seeing less avalanche activity in the Rockies side of this region the potential for these type of avalanches remains there as well.
Up to 40 cm of storm snow from earlier in the week sits over wind affected surfaces. Expect deeper deposits on north and east facing slopes, from previous west through south winds. Wind slabs may be found on all aspects due to variable winds in the past few days. A melt-freeze crust covers the surface of steep solar slopes
Buried surface hoar sits 30-60 cm deep in sheltered terrain features, and a thin sun crust exists at the same depth on steep south-facing terrain. Several other layers from January can also be found in the top 100cm of the snowpack.
The lower snowpack is made up of a widespread layer of large, weak basal facets and depth hoar in some areas. this weakness has been responsible for a number of recent very large, destructive avalanches and will continue to be a concern.
Tuesday Night
Clear skies. Southeasterly winds 10-20 km/h. Treeline temperatures, low of -10.
Wednesday
Mainly sunny. Easterly winds 15-25 km/h. Treeline temperatures, high of -9.
Thursday
Mainly sunny with a few clouds. Southerly winds 10-20 km/h. Treeline temperatures, high of -14.
Friday
Partly cloudy and isolated flurries, 2-5 cm accumulation. East winds 10-25 km/h. Treeline temperatures, high of -14.
More details can be found in the Mountain Weather Forecast.
