Avalanche Forecast
Purcells
Recent new snow combined with wind has promoted wind slab development as well as cornice growth. As the clouds part in the coming days remember that the sun packs a punch this time of year.
Avalanche Problem 1: Wind Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Be cautious as you transition into wind affected terrain.
- Use ridges or ribs to avoid pockets of wind loaded snow.
- Extra caution needed around cornices with current conditions.
Avalanche Problem 2: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
An interface buried up to 90cm deep "woken-up" last week. 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
Reports from Friday consist primarily of natural and explosive triggered wind slab avalanches size 1.5 to 2.5 in the alpine and at treeline on northerly and westerly aspects. There are also reports of two size 1 remotely triggered avalanches (from a distance) on a west aspect in the alpine. On Thursday there was a report of naturally occurring size 2.5 persistent slab avalanche on northeast facing slope at 2400m. This was reported to be triggered from a falling piece of glacier ice.
Snowpack Summary
Another 10-20cm of new snow Friday into Saturday brings storm snow amounts for the last week to 50-80cm (higher amounts in the south and west parts of the region). This new snow has been redistributed into wind slabs in wind-exposed terrain by primarily south, southwest and southeast wind. 60-90cm 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. We are 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 faceted 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
SUNDAY: Mix of sun, cloud and isolated flurries / Light to moderate southwest wind / Alpine temperature -8
MONDAY: Mix of sun, cloud and isolated flurries / Light to moderate west wind / Alpine temperature -7
TUESDAY: Mix of sun, cloud and isolated flurries / Light to moderate west wind / Alpine temperature -4
NOTE: The convective flurries which are common during this time of year can result in widely varying snowfall amounts throughout a region. These spring squalls routinely drop 20+ cm of snow in one valley while the adjacent drainage remains dry. For this reason, the distribution of avalanche problems associated with new snow, such as wind slabs, can vary greatly within a region.
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New snow and several days of southerly now switching to northerly wind means localized slabs on the leeward side of ridges and on cross-loaded slopes and gulleys. Anticipate old buried wind slabs on a variety of aspects.