Avalanche Forecast

Issued: Apr 9th, 2012 10:14AM

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

jfloyer, Avalanche Canada

South Columbia.

Spring conditions mean you should anticipate a daily cycle of loose snow avalanches on south-facing slopes.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain

Weather Forecast

This region should remain dry on Tuesday. Freezing levels are expected to go to around 3200 m, with cloud but also good periods of sunshine. Winds light southeasterly. On Wednesday, increasing cloud cover in the afternoon will make things feel a little cooler, but freezing levels are still expected to be around 3000m. Trace amounts of precipitation could occur later in the day. On Thursday, precipitation is expected, which is expected to be heavy in the south of the region (Kaslo, 20-30 mm) and moderate in the north (Revelstoke 10-15 mm); this may fall as rain in many areas. Freezing levels falling through the day from 2000 m initially to 1500 m by the end of the day.

Avalanche Summary

On Sunday, solar activity was reported up to size 2. A size 1.5 skier-triggered avalanche was reported on a north aspect at treeline with a fracture depth of around 30 cm. On Saturday a large (size 3) naturally-triggered avalanche released on a southwest aspect at 2300 m. The avalanche initiated in a shallow rocky start zone and initially pulled out the recent storm snow before stepping down to lower layers, in some places scouring all the way to ground. Another large (size 2.5) avalanche occurred on a northwest aspect at 2300 m and ran all the way to ground.

Snowpack Summary

Up to 80cm of recent storm snow sits on a weak layer of facetted crystals sitting on a crust in the alpine and at treeline. This layer still reacts to snowpack testing producing sudden, "pop" results. Recent reports of remotely triggered avalanches are noteworthy and suggest the problem will not heal quickly. Wind slabs are reported to be isolated to the immediate lee of exposed features at high elevations. Spring-like, moist snow exists on all south facing slopes as well as many north facing areas. There is limited crust recovery developing at night. There is still concern for the mid-February buried surface hoar layer that is down about 140-220 cm. Avalanches releasing on this layer are a low probability-high consequence situation. Cornices in the region are very large. With warmer temperatures, and longer periods of direct solar radiation, these may become weak and fail. They could provide a large enough trigger to release these deep layers on slopes below. Cornices are large and sagging due to recent warm temperatures.

Problems

Wet Slabs

With prolonged warm temperatures, wet slabs become more likely on a crust buried 50-80 cm, or on deeper snowpack layers. The danger is activity will start to migrate around to more northerly aspects.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

3 - 7

Loose Wet

Expect loose snow avalanches to occur on steep south-facing terrain in the afternoon, or by late morning if the sun is strong.

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

Elevations: All elevations.

Likelihood

Certain

Expected Size

1 - 5

Deep Persistent Slabs

While still unlikely, a couple of recent events indicate deeply buried weak layers have the potential to wake up and produce large avalanches during periods of prolonged warming or from heavy triggers such as cornices or step-down avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

4 - 7

Valid until: Apr 10th, 2012 9:00AM