Avalanche Forecast

Issued: Apr 17th, 2018 4:47PM

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

cgarritty, Avalanche Canada

South Columbia.

Sunshine and warming are set to maintain heightened avalanche danger over the coming days. There's a lot of new snow on the ground to feed both slab and loose wet avalanche problems.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

Wednesday: A mix of sun and cloud. Light south winds. Freezing level rising to 1800 metres with alpine high temperatures around -3.Thursday: A mix of sun and cloud. Light southwest winds. Freezing level rising to 2100 metres with alpine high temperatures around 0 to +1. Weak overnight cooling.Friday: Cloudy with flurries beginning in the evening and continuing overnight. Light to moderate southwest winds. Freezing level to 2200 metres with alpine high temperatures around 0 to +1.

Avalanche Summary

Poor visibility hindered observations of avalanche activity on Monday.On Sunday, warming and sunny breaks initiated widespread natural storm slab and loose, wet avalanche activity in the recent storm snow, up to size 2, on all aspects from 1500-2300 m.Saturday saw widespread avalanche activity with natural, cornice, skier, and explosive triggered storm slab releases (size 2-2.5) on all aspects in the alpine and in immediate lee areas at treeline.On Friday there were reports of several natural storm slab releases up to size 2 on alpine, northeast through southeast aspects.On Thursday there was a report from neighboring Glacier National Park of a size 4 slab that is thought to have been cornice triggered on a north aspect at 2800 m.

Snowpack Summary

About 30-40 cm of new snow overlies a crust on all aspects to at least 2300 m (and possibly higher on south-facing slopes), while 50-60 cm of storm snow can be found at higher elevations. Below 2400 m this new snow has a surface crust becoming moist or wet by the afternoon.Within the upper snowpack there are now a few different crusts with only the shallowest of these remaining a concern as the uppermost layer of storm snow settles and bonds to it.There is some lingering concern around the mid-March persistent weak layer in the alpine where it is found 80 to 120 cm below the surface. This buried crust/surface hoar interface was widely reactive but has not produced any avalanche activity in the past week. It is likely trending towards dormancy, but we need to keep it in the back of our minds as it is capable of producing large avalanches should it be triggered (think larger triggers such as; sleds, step-down from a surface avalanche or, a cornice collapse).Deeper persistent weak layers from December and January are considered dormant at this time.

Problems

Loose Wet

Forecast warming temperatures and sunshine are likely to destabilize surface snow and initiate loose wet activity, especially below treeline and on steep south facing features. The likelihood of cornice failures also increases with sun and warming.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.Cornices become weak with daytime heating. Avoid traveling on slopes below them.

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

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2.5

Storm Slabs

Storm slabs formed after the last round of snowfall may remain reactive to human triggering on Tuesday. The greatest caution is needed around steep or convex terrain as well as sun-affected slopes where slabs formed over a recent crust.

Exercise increased caution around south aspects where new snow may have formed a slab over crust.Watch for signs of instability such as shooting cracks or recent avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2.5

Valid until: Apr 18th, 2018 2:00PM