Avalanche Forecast
Purcells
Wind slabs up to 50 cm deep may remain sensitive to human triggering in the alpine. Persistent slabs may roar back to life over the next few days as we go through a significant warm up. South facing slopes are especially suspect and are best avoided.
Avalanche Problem 1: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Minimize exposure to steep south-facing slopes where recent storm snow overlies a crust.
- Use caution around sheltered steep or convex slopes where buried surface hoar may be preserved.
- Pay attention to overhead hazards like cornices which could trigger persistent slab avalanches.
Avalanche Problem 2: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
A few more cm of new snow are expected Saturday night with moderate northwest wind which will likely form fresh shallow slabs immediately lee of ridge crest. If the sun breaks through the clouds Sunday it may initiate natural avalanche activity.
Travel and Terrain Advice
- Be especially careful with wind loaded pockets near ridge crests and roll-overs.
- Be cautious of sluffing in steep terrain.
- Saturday's snow may be hiding recently formed wind slabs up to 50 cm deep in the alpine.
Avalanche Summary
A small human triggered wind slab avalanche was reported from the central portion of the region on an east facing slope at 2500 m on Friday.
On Thursday a skier accidently triggered a large persistent slab avalanche on a south facing feature at 2600 m. The size 2 avalanche had a crown 60 cm in depth and failed on the mid March Persistent Weak Layer (PWL). Explosive control work produced cornice failures and storm slabs to size 2.5 on a variety of aspects in the alpine. Loose wet avalanches ran naturally to size 1.5 on steep south facing alpine slopes as well.
Reported avalanche activity was limited on Wednesday; a cornice failure produced a size 2 soft slab in steep rocky terrain on an unknown aspect and sluffing was observed in steep terrain to size 1.
Snowpack Summary
Recent wind and cold snow have formed wind slabs 10 to 40 cm in depth in the alpine that sit on a mix of crusts and surface hoar. Test profiles show resistent planar failures at this interface. In wind sheltered terrain Saturday's new snow is coming to rest on a surface crust that exists on all aspects aside from true north below 2000 m. This crust extends up to around 2400 m on south facing slopes. On north facing slopes above 2000 m, temperatures have remained cold and the snowpack is still quite "winter-like."
The mid-March Persistent Weak Layer (PWL) is now 40 to 90 cm below the surface. This layer is composed of a crust on all aspects at low elevations. At upper elevations the layer presents as a crust on solar aspects (south and west) and buried surface hoar on polar aspects (north and east). The likelihood of triggering a deeper persistent slab avalanche is steadily decreasing but the consequence of doing so remains high. Solar aspects are expected to be the most suspect as the freezing level begins to rise over the next few days.
Deeper persistent weak layers from January and December are still being reported by professional observers, but are generally considered dormant.
Weather Forecast
Continued snowfall is expected Saturday night as an unstable air mass fuels convective precipitation. A ridge is expected to build offshore Sunday allowing the entire province to dry out. A more spring-like pattern begins to take shape on Monday with freezing levels creeping towards 2500 m by Tuesday.
SATURDAY NIGHT: Overcast, freezing level around 750 m, light to moderate northwest wind, 1 to 5 cm of snow possible.
SUNDAY: Broken cloud cover, freezing level beginning around 500 m rising to about 2000 m, light to moderate northwest wind, 1 to 2 cm of snow possible.
MONDAY: Scattered cloud cover, freezing level beginning around 1500 m rising to about 2200 m, light west/southwest wind, no significant precipitation expected.
TUESDAY: Scattered cloud cover, freezing level beginning around 1500 m rising to about 2500 m, light to moderate south/southwest wind, no significant precipitation expected.
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Weak crust and surface hoar 40 to 90 cm below the surface have shown prolonged reactivity since the last storm. South facing features have been the most reactive as of late, and this trend is expected to continue as temperatures rise next week.