Avalanche Forecast

Issued: Mar 12th, 2016 7:17AM

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

jlammers, Avalanche Canada

Purcells.

Buried weak layers have the potential for very large avalanches. Conservative terrain selection is still required.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Saturday night: 5-15cm of new snow / Strong southwest ridgetop winds / Freezing level at about 1500mSunday: Light flurries with possible sunny breaks / Light to moderate ridgetop winds / Freezing level at about 1400mMonday: 8-12cm of snow / Moderate easterly ridgetop winds / Freezing level at about 1300mTuesday: Mix of sun and cloud / Light ridgetop winds / Freezing level at about 1200m

Avalanche Summary

On Thursday numerous naturally triggered wind slabs (mostly in the size 2 range) were observed at treeline and in the alpine. They occurred in response to new snow and wind. On Friday explosives control continued to produce storm slabs to size 2.5 on a variety of aspects throughout the region. Of note, a size 2.5 persistent slab avalanche was triggered with explosives in the Dogtooth Range. The mid-February layer was the likely culprit in the avalanche. More wind slab activity is expected in response to wind and snow forecast for Saturday night.

Snowpack Summary

Snowfall accumulations on Thursday were in the 10-20cm range. Strong southerly winds redistributed these accumulations into touchy wind slabs at treeline and in the alpine. 30-70 cm recent storm snow overlies a prominent weak layer buried on or around Feb-27. The deepest snow amounts appear to be in the west central area near Kootenay Lake. The Feb-27 weak layer comprises surface hoar and a crust. Recent snowpack test results are mixed, with some tests indicating this layer is gaining strength, while others indicating it can still fail with sudden "pop" results. A deeper weak layer from mid-February is now down 50-80cm. The early January surface hoar/facet layer is typically down 70-120cm. Triggering an avalanche on either of these layers has become unlikely but either still has the isolated potential to produce very large avalanches with a heavy trigger.

Problems

Wind Slabs

New snow and wind will form new wind slabs in upper elevation lee terrain. The new snow may also be hiding older, larger wind slabs which formed on Thursday.

The recent snow may now be hiding windslabs that were easily visible before the snow fell.>Be cautious as you transition into wind affected terrain.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

Persistent weaknesses lie buried in the top 90cm of the snowpack. Although these layers are slowly becoming less likely to trigger, they have the potential to surprise with nasty consequences. I'd continue riding with a conservative mind set.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

3 - 5

Cornices

Large cornices loom over open bowls and alpine faces. Not only are massive cornice falls a hazard in themselves, but they can also act as a heavy trigger for slab avalanches on the slope below.

Pay attention to overhead hazards like cornices.>Stay well back from cornices.>

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Mar 13th, 2016 3:00PM