Avalanche Forecast

Issued: Mar 21st, 2017 8:02AM

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

danyelle magnan, Parks Canada

Glacier.

We are entering a tricky Low Probability, High Consequence cycle. The reality is that large, likely un-survivable avalanches continue to occur sporadically and are very hard to predict. Manage your exposure and be conservative in terrain selection!

Summary

Weather Forecast

This week expect unsettled weather. Today should be mainly cloudy, with isolated flurries and moderate S'ly winds. Freezing levels will rise to 1900m with an alpine high of 0'C. Overnight the flurries should accumulate to ~6cm. Wednesday will be similar with another 7cm expected and freezing levels to 1700m. On Thursday expect a few sunny breaks.

Snowpack Summary

In the last week a series of storms dumped over 150cm of heavy snow (rain below 1700m), with extreme winds (100+km/h) and warm temps. Overnight the winds shifted to N'ly, and are now reverse loading lee slopes. Below ~1700m a rain crust caps a moist and weak upper snowpack. The cornices are huge and have been failing providing a large trigger.

Avalanche Summary

The snowpack has demonstrated it's potential to produce very destructive avalanches. For example, on Sat Macdonald West Shoulder avalanched naturally ripping out mature timber and running to the valley floor. Sporadic avalanches continue to occur, like this one yesterday in the Smart drainage, showing wide propagation and multiple step down layers.

Confidence

Due to the number of field observations

Problems

Storm Slabs

It will take time for the storm slabs to stabilize. Snowpack tests in the region yesterday show that it is still reactive, and N'ly winds overnight will have reverse loaded lee slopes potentially re-awakening slabs in those areas.

If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 3

Persistent Slabs

It is an impressive and humbling time to be traveling in the back-country. Very large avalanches have been occurring, even logging mature timber. The scary thing is, these large avalanches continue to occur sporadically and are very hard to predict.

Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.Choose regroup spots that are out of avalanche terrain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

3 - 4

Cornices

Lots of snow combined with strong winds rapidly added to cornices. Cornice failures continue to be observed daily, and have been the trigger for many large deep avalanches.

Pay attention to overhead hazards like cornices which could easily trigger deep slabs.Minimize exposure to overhead hazard from cornices.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Mar 22nd, 2017 8:00AM