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Avalanche Forecast

Archived

Mar 20th, 2020–Mar 21st, 2020

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.

Regions

Purcells.

Clouds may temper day-time warming. Minimize exposure to cornices and steep slopes that face the sun during the warmest part of the day. A deep weak layer remain a concern.

Confidence

High - Confidence is due to a stable weather pattern with little change expected.

Weather Forecast

Friday night: Clear, light northwest wind, alpine temperature -12 C, freezing level valley bottom.

Saturday: Partly cloudy, light southwest wind, alpine temperature -8 C, freezing level 1600 m.

Sunday: Increasing cloud, light southwest wind, alpine temperature -7 C, freezing level 1600 m.

Monday: Mostly cloudy, scattered flurries with up to 5 cm of snow, light southwest wind, alpine temperature -6 C, freezing level 1500 m. 

Avalanche Summary

Over the past several days, avalanche activity was reported as natural loose wet avalanches (size 1-2.5) running in steep, sun-exposed terrain in the alpine. One large (size 2.5) cornice failed as a result of explosive mitigation.

On Monday, there was a report of a skier remotely triggering (from a distance) a large (size 2) deep persistent slab avalanche at 2600 m on a northwest aspect. The avalanche was triggered from a thin spot, released 40-80 cm deep, and ran on depth hoar near the base of the snowpack.

If you decide to travel in the backcountry, consider sharing your observations via the Mountain Information Network (MIN) to supplement our data stream as operators are shutting down. Even just a photo of what the day looked like would be helpful.

Snowpack Summary

Surface conditions are highly variable with a mix of crusts, moist snow, hard wind slabs, and soft faceted snow. Reports indicate that surface hoar may be developing on the surface on sheltered, shady slopes. Cornices are large, looming, and weakening with warm temperatures and strong solar radiation.

A weak layer of surface hoar buried February 22 may be found 50-100 cm deep. Sheltered north, northeast, and east facing slopes near treeline are the most likely locations to find this layer. Avalanche activity on this layer was last reported March 11th. There is a low likelihood of triggering an avalanche on this layer, but the consequences of doing so would be high.

Deeply buried facets lurk near the bottom of the snowpack. This layer has been responsible for sporadic deep persistent slab avalanches, usually triggered from shallow, rocky start zones.

Terrain and Travel

  • Back off slopes as the surface becomes moist or wet with rising temperatures.
  • Small avalanches can have serious consequences in extreme terrain. Carefully evaluate your line for wind slab hazard before you commit to it.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
  • Make observations and assess conditions continually as you travel.

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.