Avalanche Forecast
Regions: Lizard-Flathead.
Wind slabs will form in lee terrain features and below ridges with moderate to strong southwest wind. Be alert to conditions that change with elevation and wind exposure.
Confidence
Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.
Weather Forecast
Sunday night: Clear, moderate southwest wind with strong gusts, treeline low around -7 °C, possible inversion.
Monday: Sunny with increasing clouds in the afternoon, moderate to strong southwest wind, treeline high around -3 °C, freezing level at valley bottom.
Tuesday: Cloudy, up to 10 cm new snow, moderate to strong southwest wind gusting to extreme, treeline high around -1 °C, freezing level rising to 1500 m.
Wednesday: Cloudy, 10-20 cm new snow and rain at lower elevations, strong southwest wind gusting to extreme, treeline high around +2 °C, freezing level rising to 1800 m.
Avalanche Summary
On Saturday, storm slab avalanches up to size 2.5 were triggered by explosives. Overnight, a large (size 3.5) natural storm slab avalanche released and a large (size 2.5) cornice failure occurred.Â
On Friday, storm slab avalanches released naturally up to size 2.5. Explosives triggered storm slabs to size 2.5, and skiers triggered avalanches to size 2. A large (size 2) natural cornice failure was reported likely having failed in the overnight storm.
Evidence of a natural storm slab avalanche cycle size 2-2.5 was observed on NE aspects Wednesday and Thursday, likely having run during the storm earlier in the week.Â
Last week on Sunday, a size 2.5 persistent slab avalanche was triggered on an E aspect at treeline. This avalanche is detailed in a MIN post and features in our latest blog post, Photos of recent persistent slab avalanches in the southern interior.
Snowpack Summary
The recent storm snow totals 40-50 cm. In open terrain and upper elevations, wind developed more reactive deposits around lee and convex features. This recent snow covered a hard, faceted snow surface which formed during cold temperatures and may take a little time to bond.Â
The most notable layer of concern in the snowpack is a crust that was formed in early December and is now down 100-270 cm. Activity on this layer has been sporadic, the most recent persistent slab avalanche in the region was on January 2. This layer has created a low likelihood, high consequence scenario which is best managed through conservative terrain choices and disciplined backcountry travel techniques.
Terrain and Travel
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
- Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
Avalanche Problems
Wind Slabs
Moderate to strong southwest wind will continue to redistribute the recent snow. Expect to find more reactive deposits around ridge features. Be especially mindful around steep and convex openings in the trees. The new and recent snow may overlie a weak interface which could result in deeper and touchier than expected slabs.
Aspects: North, North East, East, South East, North West.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 1.5 - 2.5
Persistent Slabs
A persistent slab problem formed by a crust down 100-270 cm has created a low likelihood, high consequence scenario that is difficult to forecast. Avoid likely trigger spots such as steep, rocky slopes with a shallow or thin to thick snowpack.
The same feature or path can slide repeatedly when the persistent weak layer gets reloaded by new snow.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Unlikely - Possible
Expected Size: 2 - 3.5