Avalanche Forecast

Issued: Jun 15th, 2016 3:00PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Storm Slabs and Persistent Slabs.

jlammers, Avalanche Canada

Kootenay Boundary.

A series of storms will start Wednesday night and continue through the weekend. Avalanche conditions will get spicy! If more than 20 cm new snow falls Wednesday night, Thursday's ratings should be increased to HIGH.

Summary

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain on Thursday

Weather Forecast

Wednesday night: A moderate storm pulse is expected to bring 10-15 cm new snow to this region overnight, with strong (50-60 km/h) southwesterly winds and freezing levels around 1000 m.Thursday: 5-10 cm new snow expected. Continued strong southwesterly winds. Freezing level remaining at 1000 m.Friday: The second storm pulse is expected to bring 15-20 cm new snow. Strong southerly winds. Freezing level rising to around 1200 m.Saturday: The third and biggest storm pulse is expected to bring around 30 cm new snow. Strong southwesterly winds. Freezing level around 1000 m.

Avalanche Summary

Recent storms have promoted numerous storm slab avalanches to size 2. Most of these avalanches failed naturally or under light loads, and were noted at treeline and in the alpine on north through east-facing terrain. The surface hoar layer which formed a few weeks ago continues to produce isolated slab avalanches to size, 3 especially at treeline where it is thought to be well-preserved. In most cases, these avalanches occurred on steep, unsupported slopes, and required a large trigger like a cornice fall or an avalanche in motion. New snow and wind forecast for the next few days will encourage ongoing storm slab activity. Storm loading will also increase the size and likelihood of avalanches failing on the buried surface hoar layer.

Snowpack Summary

Up to 50 cm of snow has fallen over the past 3 days. Strong southwest winds have redistributed these accumulations into much deeper slabs on north through east-facing terrain at treeline and in the alpine. About 80 cm below the surface, you'll likely find a widespread layer of surface hoar which formed a few weeks ago. Although this interface is gradually gaining strength, it continues to produce sudden results in snowpack tests and has the potential to produce large avalanches in isolated terrain. Increased reactivity at this interface has been noted on shady aspects at treeline. Below this, the snowpack is generally strong and well settled.

Problems

Storm Slabs

Ongoing storm loading over the next few days will form new storm slabs and gradually increase the avalanche danger. I'd be especially cautious on wind-loaded features at treeline and in the alpine.

Stay off recent wind loaded areas until the slope has had a chance to stabilize.>Enter your line well below ridge crests to avoid wind loaded pillows.>Be alert to conditions that change with elevation.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

A tricky layer of surface hoar lies up to 80 cm below the surface, and has recently produced isolated yet destructive avalanches. I'd give this layer more time to gain strength before committing to steep, unsupported terrain.

Conditions have improved, but be mindful that deep instabilities are still present.>Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>Choose well supported terrain without convexities.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

3 - 5

Valid until: Jun 16th, 2016 2:00PM