Avalanche Forecast

Issued: Mar 14th, 2016 9:16AM

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

jlammers, Avalanche Canada

Purcells.

As stormy weather tapers-off and a dry ridge gradually builds over the province, solar radiation may become the driver for natural avalanche activity.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Light snowfall (2-3cm) is expected on Tuesday and early Wednesday. Clouds are expected to scatter throughout the day on Wednesday, while clear skies are forecast for Thursday. Ridgetop winds are expected to be generally light to moderate and southwesterly on Tuesday, switching to northwesterly by Wednesday. Daytime freezing levels should hover around 1200m for the forecast period.

Avalanche Summary

A natural wind slab avalanche cycle to size 2.5 was observed in mostly northeast facing alpine terrain on Sunday. The activity occurred in response to new snow and strong southwest winds on Saturday night. A size 2 persistent slab avalanche was also noted on Sunday in the Dogtooth Range. The avalanche, which failed on a northeast aspect at 2200m, started as a smaller wind slab and stepped-down to the late February layer. On Monday, explosives control triggered another size 2 persistent slab avalanche on a north facing alpine slope.

Snowpack Summary

On Saturday night, 8-15cm of new snow fell. Strong southwest winds redistributed these accumulations into touchy wind slabs at treeline and in the alpine. 35-70 cm below the surface you'll find a persistent weak layer comprised of surface hoar, facets and/or a thick crust. This layer, which was buried on February 27th, seems variably reactive. In other words, it's still really touchy in some places while in other places it's really tough to trigger, and there's not much of a reliable pattern telling us what exact aspects are most suspect. I'd continue to be suspicious of steep, unsupported features at treeline and in the alpine as this layer has the potential for large avalanches. Deeper weak layers from mid-February and early January are now down 50-90cm and 70-120cm respectively. 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 or significant warming.

Problems

Persistent Slabs

A persistent weak layer continues to produce intermittent large avalanches. Although this layer is slowly becoming less likely to trigger, it has the potential to surprise with nasty consequences. I'd continue riding with a conservative mind set.

Choose well supported terrain without convexities.>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 - Likely

Expected Size

3 - 5

Wind Slabs

Recently formed wind slabs may remain sensitive to light inputs in higher elevation lee terrain. Brief periods of solar radiation may also promote loose wet avalanche activity on steep, sun-exposed slopes.

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: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Cornices

Large cornices loom over open bowls and alpine faces. Not only are massive cornice falls a hazard in themselves, 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 15th, 2016 2:00PM