Avalanche Forecast

Issued: Apr 17th, 2018 4:47PM

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

cgarritty, Avalanche Canada

North 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 1700 metres with alpine high temperatures around -5.Thursday: A mix of sun and cloud. Light south winds. Freezing level to 2000 metres with alpine high temperatures around -2. Weak overnight cooling.Friday: Cloudy with light flurries and a trace of new snow, increasing overnight. Light southwest winds. Freezing level to 2000 metres with alpine high temperatures around -1.

Avalanche Summary

Reports from Monday were limited by poor visibility but included one small (size 1, 20 cm deep) ski cut wind slab as well as skier-triggered loose snow releases on steeper slopes. The rough dividing line between loose wet and loose dry activity was about 2000 metres.Sunday's warm weather, rain and sunny breaks produced a widespread loose, wet avalanche cycle from size 1.5-3 on steep, solar aspects from 1600-2600 m, in the afternoon.Saturday there were reports from the southeast corner of the region of natural cornice and storm slab avalanche activity (size 2-3) on north and west aspects from 2500-2700 m.On Friday a large cornice collapsed on a southeast aspect at 2500 m, with several 'bus-sized' blocks observed in the debris.Thursday there were reports from Glacier National Park of a size 4 wind slab that occurred overnight and is thought to have been cornice triggered on a north aspect at 2800 m.

Snowpack Summary

About 30 cm of recent storm snow overlies a crust on all aspects to at least 2300 m (and possibly higher on south aspects). While 40-50 cm of storm snow can be found at higher elevations in the alpine. Below 2200 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 (PWL) in the alpine where it is found 90 to 120 cm below the surface. This buried crust/surface hoar interface was widely reactive but has not produced any avalanche 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 step-down from a surface avalanche or a cornice collapse).Deeper persistent weak layers from December and January are generally considered dormant at this time but may be starting to become reactive to large triggers, such as a cornice collapse.

Problems

Loose Wet

Forecast warming temperatures and sunshine are likely to destabilize surface snow and initiate loose, wet avalanche activity especially below treeline and on steep south facing features.

If triggered the loose wet sluffs may step down to deeper layers resulting in large avalanches.Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.

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

Cornices

Large cornice failures have been reported in the past week. A cornice collapse may have the potential to trigger a deep weak layer resulting in a very large and destructive avalanche.

Give cornices a wide berth when traveling on ridges.Cornices may weaken with sun and daytime heating. Minimize your exposure to large cornices overhead.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

2 - 3.5

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