Avalanche Forecast
South Columbia
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.
- Extra caution needed around cornices with current conditions.
- Use ridges or ribs to avoid pockets of wind loaded snow.
Avalanche Problem 2: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
An weak layer buried up to 80cm deep "woke-up" last week. This problem seems most reactive in south-facing terrain where buried crusts exist.
Travel and Terrain Advice
- Carefully assess and consider avoiding southerly facing slopes.
- Pay attention to overhead hazards like cornices which could trigger persistent slabs.
- Watch convoluted terrain with variable or shallow snow depths and multiple trigger points.
Avalanche Summary
Thursday and Friday's reports focus on natural wind and storm slab avalanches size 2-2.5 at treeline and in the alpine on all aspects. Additionally there were also reports of skier triggered wind and storm slab avalanches to size 1.5 as well as a remotely triggered size 1.5 persistent slab avalanche on a northwest aspect at 1300m. Deep persistent avalanche activity has become less frequent over the past week.
Snowpack Summary
An additional 20-40cm of new snow fell Thursday through Friday, bringing the storm snow total this week to 50 to 80cm. This storm snow has been redistributed into localized wind slabs. It covers old surfaces including faceted powder, a sun crust on solar aspects, and surface hoar on shady slopes. Around 70 to 100cm 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 solar aspects where it's associated with with small facets or surface hoar.
There are several deeper layers that have shown signs of improving but still remain suspect as low probability to trigger yet will result as a high consequence avalanche if triggered. 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 snow. These layers may "wake-up" with strong inputs such as sustained warming, sustained snowfall, large triggers (e.g. cornice fall, smaller avalanches coming down from above); human triggering is also possible in shallow, rocky terrain.
Weather Forecast
SUNDAY: Mix of sun, cloud and isolated flurries / Light to moderate southwest wind / Alpine temperature -10
MONDAY: Mix of sun, cloud and isolated flurries / Light to moderate west wind / Alpine temperature -10
TUESDAY: Mix of sun, cloud and isolated flurries / Light west wind / Alpine temperature -6
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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Localized wind slabs may have formed on the down-wind side of ridges and ribs. Watch cross-loaded slopes and gullies too.