Avalanche Forecast

Issued: Apr 18th, 2018 4:18PM

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

cgarritty, Avalanche Canada

North Columbia.

Forecast sunshine and warming will increase the likelihood of triggering in a wide range of avalanche problems on Thursday. Expect stability to deteriorate over the day.

Summary

Confidence

High -

Weather Forecast

Thursday: Mainly sunny. Light southeast winds. Freezing level to 2000 metres with alpine high temperatures around -2. Weak overnight cooling.Friday: Cloudy with isolated flurries and a trace of new snow, increasing overnight. Light to moderate south winds. Freezing level to 1900 metres with alpine high temperatures around -3. Weak overnight cooling.Saturday: Cloudy with continuing flurries bringing approximately 10 cm of new snow. Light to moderate southwest winds. Freezing level to 1700 metres with alpine high temperatures around -3.

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.In addition to heightened storm slab activity following regular snowfalls, observations from late last week also showed a pattern of heightened cornice failure activity. Reports of 'bus sized' blocks found in debris as well as a suspected cornice-triggered size 4 wind slab release should keep these looming giants top of mind.Looking forward, a trend toward clearing skies and warming temperatures will be increasing chances of loose wet avalanche activity as well as testing the strength of storm slabs and wind slabs formed in the wake of recent snowfall and wind events.

Snowpack Summary

About 50-70 cm of recent storm snow overlies a crust on all aspects to at least 2300 m (and possibly higher on south aspects). Shifting strong southwest and north winds pressed and redistributed the most recent accumulations into new wind slabs on a range of aspects on Monday.Within the upper snowpack there are now a few different crusts with the shallowest of these (down 20-40 cm) 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 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.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.If triggered the loose wet sluffs may step down to deeper layers resulting in large avalanches.Manage your sluff and be extra cautious where long slopes allow for more snow entrainment.

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

Elevations: All elevations.

Likelihood

Very 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.

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

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

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

2 - 3.5

Storm Slabs

The strength of storm and wind slabs formed after the last round of snowfall will be tested by warming on Thursday. The greatest caution is needed around steep or convex terrain as well as sun-affected slopes where slabs formed over a recent crust.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 2.5

Valid until: Apr 19th, 2018 2:00PM