Avalanche Forecast
Purcells
We're still managing a midwinter snowpack at and above treeline and the persistent slab problem requires thoughtful terrain selection.
Avalanche Problem 1: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Use caution around sheltered steep or convex slopes where buried surface hoar may be preserved.
- Minimize exposure to steep south-facing alpine slopes, where buried crust may be preserved.
- Use conservative route selection, choose moderate angled and supported terrain with low consequence.
Avalanche Problem 2: Wind Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Light new snow has been redistributed by variable winds into thin wind slabs on a variety of aspects. Slabs have also been noted forming above weak layers like crust and surface hoar. Deeper slabs are likely to be found in the south of the region.
Travel and Terrain Advice
- Be especially careful with wind loaded pockets near ridge crests and roll-overs.
- Wind slabs bay be touchier in areas where they overlie crust or surface hoar.
Avalanche Summary
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.
On Tuesday a small avalanche was triggered by a skier on a northeast facing slope at 2200 m. The size 1 avalanche failed on the late March interface. Control work produced avalanches from size 2 to 3 on north/northeast facing features above 2400 m that likely ran on the late March interface as well.
On Saturday a skier triggered a large slab avalanche (size 2.5) on a south aspect at 2600 m. The avalanche failed on a buried sun crust 150-200 cm below the surface. Another large (size 2.5) wind slab released naturally from a steep southeast-facing alpine slope in the St. Mary's area. Explosives control in the northern half of the region produced numerous storm slabs ranging from size 1.5-2.5 at treeline and alpine elevations. Crown fractures ranged from 30-100 cm. All aspects were represented in results, with the majority of activity focused on northeast to northwest aspects in the alpine.
Snowpack Summary
Tuesday night's storm brought up to 8 cm of new snow with very little wind.
Storms over the past week brought variable snowfall totals of 20 to 80 cm to the region, with areas to the south of the region seeing the deepest accumulations.
This storm snow sits on a persistent weak layer buried in late March that consist of crusts below 1900 m and on south aspects, and surface hoar on shaded aspects at higher elevations.
Other slightly deeper surface hoar/facet layers have been reported on shaded aspects at higher elevations and may be found approximately 40 to 90 cm below the surface.
Deeper persistent weak layers from mid-late February as well as January and December layers, are still being monitored by professional observers, but are generally considered dormant. Facets also linger at the base of the snowpack.
Weather Forecast
The current weather pattern looks more like February than April, but we'll take it! Freezing levels are expected to rise just a bit over the next few days and light daily snowfall should continue through the weekend
THURSDAY NIGHT: Freezing level around 500 m, light variable wind, 2 to 5 cm of snow possible.
FRIDAY: Broken cloud cover giving way to scattered cloud in the afternoon, freezing level beginning at valley bottom rising to about 1000 m, light southerly wind at treeline, light northwest wind at ridgetop, trace of snow possible.
SATURDAY: Broken cloud cover, freezing level beginning at valley bottom rising to around 1000 m, light to moderate southerly wind, 2 to 6 cm of snow possible.
SUNDAY: Broken cloud cover, freezing level beginning at valley bottom rising to about 1600 m, light to moderate west/southwest wind, 1 to 3 cm of snow possible.
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A weak layer of crust and surface hoar has been buried by a variable 20-80 cm of storm snow and has shown continued reactivity since the last storm. Manage the uncertainty around triggering this layer by sticking to lower angle, supported slopes.