Avalanche Forecast
Regions: North Columbia.
The developing storm slabs are expected to be reactive to human triggers on Sunday. Careful terrain selection and route finding will be required to effectively manage risk.
Confidence
Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.
Weather Forecast
SATURDAY NIGHT: Partly cloudy, light south wind, alpine temperature -12 C, freezing level below valley bottom.
SUNDAY: 10-15 cm. snow, moderate south wind, alpine temperature -9 C, freezing level 700 m
MONDAY: Cloudy with possible flurries; 0-3 cm, light west wind, alpine temperature -11 C, freezing level 500 m
TUESDAY: Mix of sun and cloud, light southwest wind, alpine temperature -7 C, freezing level 600 m.
Avalanche Summary
Several large cornice falls have been reported over the last few days. Most of them did not trigger slabs on the slopes below. Several natural and skier triggered slab avalanches up to size 2 were reported on primarily east/southeast aspects at treeline and above on Tuesday. Human triggered avalanches are expected to increase as the new snow settles into a cohesive storm slab over the fragile layer of surface hoar.
Snowpack Summary
5-15 cm of new snow has buried a widespread layer of surface hoar (size 10-20 mm.). This layer exists on all aspects and elevations except for steep solar aspects where it was melted by sun and windward alpine slopes where the layer was flattened by wind before being buried. Surface hoar sitting on a thin sun crust has been reported on lower angle solar aspects which is a particularly nasty combination. The new snow will likely become increasingly reactive as it settles into a cohesive slab. The early February rain crust down 60-80 cm. is another prominent layer in the upper snowpack that requires monitoring, though there have been no recent avalanches on this layer. The mid and lower snowpack is generally well settled and strong.
Terrain and Travel
- Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.
- Be alert to conditions that change with elevation, aspect and exposure to wind.
- Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.
- Cornice failure may trigger large avalanches.
Avalanche Problems
Storm Slabs
The new snow may be more reactive than expected; especially on slopes where it has been wind loaded and is sitting on a layer of fragile surface hoar.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 1 - 2