Avalanche Forecast

Issued: Apr 10th, 2012 10:46AM

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

jlammers, Avalanche Canada

South Columbia.

Summary

Confidence

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

Weather Forecast

Wednesday: increased cloud with light precipitation developing in the late afternoon becoming moderate in some areas overnight / moderate southerly winds / freezing level at 2800m Thursday: light precipitation / moderate westerly winds / freezing level at 1700m Friday: a mix of sun and cloud / moderate westerly winds / freezing level at 1700m

Avalanche Summary

Over the past few days, many small and large wet loose snow avalanches occurred in response to daytime warming and direct solar radiation. Numerous size 2-3.5 slab avalanches also occurred on sun-exposed aspects, with more isolated activity on shaded aspects. One report indicated a wet loose snow avalanche that triggered a slab that most likely ran on the mid-February surface hoar.

Snowpack Summary

Up to 80cm of snow overlies 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 with 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 and solar radiation, wet slabs become more likely on a crust buried 50-80 cm, or on deeper snowpack layers. With rising freezing levels, activity will start to migrate around to more northerly aspects.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

3 - 7

Loose Wet

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

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

Elevations: All elevations.

Likelihood

Very Likely - 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 11th, 2012 9:00AM