Avalanche Forecast

Issued: Feb 14th, 2015 7:53AM

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

triley, Avalanche Canada

Kootenay Boundary.

A Special Public Avalanche Warning is in effect for this region. The cooling trend is expected to begin overnight, but daytime heating and strong solar radiation may continue.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain

Weather Forecast

Mostly clear overnight with freezing levels dropping down to about 1000 metres by morning. Light northwest winds overnight and during the day on Sunday. Some lingering cloud during the day as freezing levels rise up to about 1500 metres. Clear overnight and Monday with freezing levels down to valley bottoms by morning and then rising up to about 1500 metres with light winds and strong solar radiation. Another good freeze to valley bottom is expected by Tuesday morning, and then the freezing level should rise up to about 1500 metres with light winds and strong solar radiation.

Avalanche Summary

Reports from Friday include natural loose wet and wet slab avlanches up to size 2.5. Reports from Thursday include isolated large explosive triggered persistent slab avalanches failing on the mid-January surface hoar on northeast facing treeline and alpine slopes. These slabs were 80-150 cm thick with some wind-loaded pockets as deep as 2 m. One avalanche was described as 'sluggish', but highly destructive, taking out mature timber on the way down.

Snowpack Summary

Recent warm temperatures have softened the upper snowpack, reawakening deep persistent weaknesses in isolated areas. As temperatures continue to fluctuate and stress the snowpack, expect an increased likelihood of triggering large destructive avalanches in isolated areas (e.g. thin spots) with heavy triggers (e.g. cornice falls, stuck sleds spinning tracks, or groups of people). Approximately 65-100 cm of recent storm snow is bonding well to a crust buried at the beginning of February; however, this bond is much weaker where surface hoar overlies the crust. Below that, recent snowpack tests gave moderate to hard but sudden collapse results on the mid-January surface hoar where it was found down 70-82 cm on a northeast facing treeline slope. This persistent weakness has been found as deep as 110 cm, or deeper on wind-loaded slopes. The mid-December crust/facet/surface hoar weakness may be persisting in the mid to lower snowpack at higher elevations.

Problems

Deep Persistent Slabs

Deep persistent weaknesses recently woke up with the warm temperatures and should be treated with suspicion until after things freeze up again. Although likely to need a large trigger, the potential consequences are dire.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>Be aware of thin areas that may propagate to deeper instabilities.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Storm Slabs

Warm temperatures and sunshine could destabilize the recent snow resulting in isolated slab activity and loose wet sluffs, particulary on steep sun-exposed slopes.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 5

Cornices

Cornices will likely become unstable with fluctuating temperatures. Not only are they a hazard in themselves, but they are also large triggers for deep slab avalanches on the slope below.

Cornices become weak with daytime heating. >Give cornices a wide berth when travelling on or below ridges.>

Aspects: North, North East, East, South East.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Valid until: Feb 15th, 2015 2:00PM