Avalanche Forecast

Issued: Jan 28th, 2015 7:58AM

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

triley, Avalanche Canada

Kootenay Boundary.

Spring conditions with overnight freezing and daytime warming.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain on Thursday

Weather Forecast

The freezing level should drop to valley bottoms overnight, and then rise back up to about 1500 metres during the day. Expect continued sunny skies and light winds during the day on Thursday. We should see another good re-freeze to valley bottoms overnight and into Friday morning as the cooling continues. More sun and light winds on Friday. Saturday should be cooler with cloud and moderate Southwest winds developing in the morning, and light precipitation starting overnight.

Avalanche Summary

There are no new reports of avalanches. On Monday there were several size 2.0-2.5 loose wet and wet slab avalanches released with explosives at Kootenay Pass, and a size 3.0 natural avalanche in the backcountry near Whitewater ski resort on a Southeast aspect with a very wide propagation that probably released on the mid-January persistent weak layer during a period of strong solar radiation. Moist or wet loose snow avalanches have been reported from several areas up to size 2.0 over the past few days during the warming event. On Saturday a skier triggered a size 2 persistent slab which failed on the mid-December layer. This was a surprising result because it was on a well-supported, concave terrain feature (which had also been heavily skied).

Snowpack Summary

The cool down has started. Overnight freezing down to valley bottoms has created melt-freeze crusts. Strong solar radiation and warm temperatures are affecting the surface layers and turning them moist or wet. We are in a spring like diurnal freeze/thaw cycle. Periods of warming has increased the likelihood of triggering the persistent weak layer of mid-Jan surface hoar layer which is down about 20-60 cm. These large, well-preserved surface hoar crystals sit on a thin crust up to about 1900m on north aspects and all the way to ridgeline on south aspects. A deeper crust/surface hoar combo buried in mid-December is typically down 80-120cm and has produced some large avalanches recently.

Problems

Persistent Slabs

Continued warming from high freezing levels and strong solar radiation may result in natural avalanches releasing on the buried persistent weak layer on Southerly aspects. Avalanches may be human triggered on all aspects.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>Choose well supported terrain without convexities.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 4

Loose Wet

Moist or wet loose snow is expected to continue to release from light additional loads, or from strong solar radiation on Southerly aspects.

Minimize exposure to sun exposed slopes when the solar radiation is strong.>Be aware of party members below you that may be exposed to your sluffs.>

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

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Deep Persistent Slabs

Very warm temperatures and high freezing levels may result in deeply buried weak layers reacting to large loads like cornice falls or from light loads in thin snowpack areas.

Avoid common trigger points such as convexities, thin or variable snowpack areas and around rocks.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

3 - 5

Valid until: Jan 29th, 2015 2:00PM