Avalanche Forecast
Regions: Northwest Inland.
The recent snow has added load to buried weak layers and may still be reactive to human triggers. Conservative terrain selection is recommended.
Confidence
Moderate - Uncertainty is due to the complexity of the snowpack’s structure.
Weather Forecast
TUESDAY NIGHT- Mainly cloudy with clear periods / west wind, 30-60 km/h / alpine low temperature near -12
WEDNESDAY- Cloudy with sunny periods and isolated flurries / west wind, 40-60 km/h / alpine high temperature near -11
THURSDAY- Cloudy with sunny periods / northwest wind, 20-30 km/h / alpine high temperature near -12
FRIDAY- Sunny / northeast wind, 30-60 km/h / alpine high temperature near -13
Avalanche Summary
Fresh snow and strong winds have promoted storm slab development, especially at upper elevations. Humans may be able to trigger these slabs, especially in wind loaded areas and in the trees, where a buried surface hoar layer may make these slabs more reactive.
Last week there were reports of wind slab, persistent slab (failing on the February 19 surface hoar layer), and deep persistent slab (failing on basal facets) avalanches. This pattern highlights loading and surface avalanches from recent stormy weather straining multiple weak layers in the snowpack.
Snowpack Summary
The storm on Monday night and Tuesday delivered 10-15 cm of new snow to the region with strong winds. This new snow is likely sitting on a weak layer of surface hoar, and/or a crust on solar aspects. There are likely widespread storm slabs at upper elevations within the new snow.
Loading from new snow and wind has made several persistent weak layers problematic over the past week. A combination of surface hoar and sun crust layers were buried on February 19 and currently sit 30-60 cm below the surface that seem to be most sensitive to human triggering at treeline elevations.
A couple of weak layers that formed in January are buried in close proximity to one another 80-140 cm below the surface. Below that, an early season crust/facet layer lurks at the base of the snowpack.
Terrain and Travel
- Continue to make conservative terrain choices while the storm snow settles and stabilizes.
- Storm slabs in motion may step down to deeper layers resulting in large avalanches.
- Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
Avalanche Problems
Storm Slabs
Fresh snow and wind has formed storm slabs in many areas, especially at higher elevations. These slabs may be more reactive to human triggers in wind loaded areas, and in the trees, where they likely rest on a buried surface hoar layer.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible - Likely
Expected Size: 1 - 2
Persistent Slabs
30 to 60 cm of settled snow rests above a widespread layer of surface hoar that produced numerous avalanches last week. These slabs have been most sensitive to triggering at treeline.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood: Possible - Likely
Expected Size: 1.5 - 2.5
Deep Persistent Slabs
Recent loading from new snow and wind has aggravated the region's deep persistent slab problem. Some very large and destructive avalanches have been sporadically failing on deeply buried weak layers, predominantly on north through east aspects in the alpine. Cornice falls are a likely trigger for these slabs.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Unlikely - Possible
Expected Size: 2.5 - 3.5