Avalanche Forecast
Purcells
Southern areas are expected to receive most of the new snow and wind. Where there's more than 20 cm of new snow Friday, Avalanche Danger Ratings may be higher than forecast.
Avalanche Problem 1: Wind Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Use caution on steep open slopes and convex rolls
- Be cautious as you transition into wind affected terrain.
- Stay off recent wind loaded areas until the slope has had a chance to stabilize.
Avalanche Problem 2: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
An interface buried up to 70cm deep has "woken-up". This problem seems most reactive in south-facing terrain where buried crusts exist.
Travel and Terrain Advice
- Watch convoluted terrain with variable snowpack depth and multiple trigger points.
- Carefully assess and consider avoiding southerly facing slopes
- Pay attention to overhead hazards like cornices which could easily trigger the deep persistent slab.
Avalanche Summary
On Wednesday only sluffing (Loose Dry) or "No New Avalanches" were reported by avy pros. Prior to that avalanche activity consisted of mainly wind slabs (skier triggered and skier remote) in the size 1-1.5 range. However, we've also received reports of persistent slab avalanches (to size 3) where recent accumulations have been the highest. These avalanches, were skier-triggered or remotely triggered (from a distance) on Monday and naturally occurring on Tuesday with wind loading on cross-loaded slopes. We suspect the buried sun crust buried mid-February. Deep persistent avalanche activity has become less frequent over the past week.
Snowpack Summary
Up to 40 cm of recent storm snow (in the south and west parts of the region) was redistributed into wind slabs in wind-exposed terrain by south and southwest flow. Up to 60cm below the surface there's a layer buried mid-February that's a sun crust on solar aspects, and spotty surface hoar on sheltered slopes. This layer looks most concerning on on solar aspects where it's associated with with small facets or surface hoar above.
There are several deeper layers that have shown signs of improving but still remain suspect as low probability - high consequence avalanche problems. I'm talking about surface hoar layer buried back in December and January. Near the base of the snowpack is a November crust combined with loose sugary snow. These layers may "wake-up" with strong inputs such as sustained warming, sustained snowfall, large triggers (e.g. cornice fall or smaller avalanches coming down from above); human triggering is also possible in shallow snowpack areas with convoluted terrain.
Weather Forecast
A weak front is stalling on a north to south axis over the region setting up a southerly wind with most snow expected in the southern parts of the region.
Friday: The important part of the weather forecast is new snow and wind overnight Thursday: up to 10-15 cm of new snow that fell with moderate south or southeast winds. Calmer and drier through the day. Temperatures staying on the negative side of zero. Possible sunny breaks, especially in the north.
Saturday: Mix of sun and cloud (sunnier in north, cloudier in south) with continued flurries or light precip (drier in the north, snowier in the south). Little wind and temperatures at treeline staying around or below -5 C.
Sunday: Compared to Saturday, Sunday looks a little bit sunnier, dry throughout the region, a bit windier (light from the SW), and similar temperatures.
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New snow and several days of south and southwest wind means localized slabs on the leeward side of ridges and on cross-loaded slopes and gulleys. Storm slabs may also be found in sheltered areas on steeper slopes and rolls.