Avalanche Forecast

Issued: Jan 28th, 2017 3:55PM

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

Avalanche Canada cgarritty, Avalanche Canada

A storm has ramped up avalanche danger throughout the region. Travel in avalanche terrain is not recommended.

Summary

Confidence

High -

Weather Forecast

Saturday night: The tapering storm will deliver another 10-15 cm in the overnight period. Winds strong from the southwest. Sunday: Mainly cloudy with scattered flurries bringing another 5 cm of new snow. Winds moderate to strong from the west. Freezing level to about 900 metres with alpine temperatures around -2. Monday: Mainly cloudy with isolated flurries and a trace of new snow. Winds light to moderate from the northwest. Freezing level dropping to 300 metres with alpine temperatures around -8. Tuesday: A mix of sun and cloud. Winds light to moderate from the northeast. Freezing level to valley bottom and alpine temperatures around -10.

Avalanche Summary

Our storm is unfortunately obscuring visibility of higher elevation terrain where the bulk of avalanche activity is expected to be ongoing. With that said, explosives control in the Stewart area on Friday yielded numerous storm slab results results to Size 2 with crown depths of 25-60 cm. Numerous loose wet avalanches have also been reported at highway elevations. Avalanche size and frequency is expected to increase as snowfall continues to accumulate. Aside from slab avalanche concerns, it should also be noted that loose wet avalanches can be expected to continue running out of steep terrain at lower elevations.

Snowpack Summary

A storm impacting the region over Friday and Saturday has delivered approximately 40-90 cm of new snow to the mountains, with the greatest depths accumulating in coastal areas. Strong to extreme southwesterly winds have accompanied the storm and lower elevations are seeing precipitation fall as rain. Snow will continue to fall over Saturday night and by Sunday morning me might expect anywhere from 70-130 cm to have accumulated above above the latest buried surface hoar layer from January 23rd. This surface hoar was previously reported growing up to size 10 mm at treeline and below and may be associated with a crust below 1100 metres. Although storm slab problems have captured our attention, there continue to be several other surface hoar layers of concern from early January and Christmas. Some reports show these persistent weak layers to be rounding and bonding, however recent reports show sudden planar releases in snowpack tests with hard forces applied. Our ongoing heavy precipitation will be a good test for these older buried weak layers.

Problems

Storm Slabs

An icon showing Storm Slabs
Storm slabs will continue to develop with forecast snowfall and wind. Avalanche size and frequency will increase with each pulse of precipitation and wind. Danger will remain elevated as the storm breaks on Sunday.
The new snow will require several days to settle and stabilize.If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

2 - 3

Persistent Slabs

An icon showing Persistent Slabs
It may still be possible to trigger large avalanches on a number of deeply buried weak layers. Storm slab avalanches may also have the potential to 'step down' to these layers. This danger will increase as new snow and wind add load to the snowpack.
Be aware of the potential for wide propagations due to the presence of buried surface hoar layers.Avoid areas with overhead hazard.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 4

Valid until: Jan 29th, 2017 2:00PM

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