Avalanche Forecast

Issued: Apr 10th, 2012 10:26AM

The alpine rating is high, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Loose Wet, Wet Slabs and Deep Persistent Slabs.

swerner, Avalanche Canada

Purcells.

Sunny skies and freezing levels as high as 3500 m are continued on Wednesday. As the snowpack deteriorates, natural avalanche activity is to be expected. Solar induced wet slabs may be large and run full path.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain

Weather Forecast

The weather pattern will begin to change tonight as a dominating ridge of high pressure will start to break down. This will allow a strengthening, moist SW flow to enter the region. Wednesday: Freezing levels will continue to be near 3200 m, with sunny skies and light Southerly winds. Thursday: Light precipitation should begin later Wednesday night, while Thursday will bring moderate amounts. Freezing levels will fall 1500 m. Ridgetop winds will be light gusting moderate from the SW. Friday: Lingering, light precipitation in the morning. Freezing levels will rise to 2000 m, with possible sunny skies in the afternoon.

Avalanche Summary

On Monday, numerous natural slab avalanches up to size 2 were reported. These occurred on solar aspects out of steep rocky terrain. On Sunday a natural cornice fall triggered a large size 3.5 avalanche. This occurred on a North aspect at 2800 m. The width of the avalanche was 100 m, running 1100 m in length. This ran on facets to ground. This may be an indicator of more to come; especially with an increase of solar radiation and high freezing levels. One other natural cornice fall triggered a size 1.5 on the slope below. This cornice chunk triggered the March 27th layer on an East aspect around 2700 m.

Snowpack Summary

Mild temperatures and solar radiation have settled out much of the upper snowpack. Spring-like conditions prevail, with surface crusts on solar aspects and melt- freeze conditions on all aspects below 1700 m. Over the next day the region will see less of a re-freeze, and higher freezing levels promoting moist snow throughout. Up to 120 cm sits on the March 27th interface. This interface consists of a sun crust on southerly aspects and a temperature crust on more northerly slopes. A thin layer of facets and or surface hoar can be found on this crust on all aspects. Be aware of avalanches running on this layer over the next few days. There is also a weak layer of facets or depth hoar in shallower snowpack areas that is suspect once the region starts seeing warm days without overnight refreeze. Cornices are reported to be very large and exist on most ridge lines. These will become weak under the direct solar influence and warming. I would stay very clear of cornices from above and below. The mid-pack is well settled and strong.

Problems

Loose Wet

Strong sun and freezing levels up to 3200 m is forecast for Wednesday. Watch for loose wet avalanches, they may step down to a deeper slab. Cornices are large and weak. Stay well away from above and below.

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

Elevations: All elevations.

Likelihood

Very Likely - Certain

Expected Size

1 - 4

Wet Slabs

A cohesive slab up to 100 cm is sitting on the March 27th interface. With little freeze and skyrocketing freezing levels, wet slabs are likely to occur on this layer. They may entrain more mass than expected and run full path.

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

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 6

Deep Persistent Slabs

The odd deep slab could still be out there, I'm still suspect of steeper unsupported slopes & places where the snowpack goes from thick to thin, especially near ridge crest and around rock outcroppings.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 7

Valid until: Apr 11th, 2012 9:00AM