Avalanche Forecast

Issued: Jan 29th, 2017 3:14PM

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

Avalanche Canada cgarritty, Avalanche Canada

Thick storm slabs have accumulated in the wake of a coastal storm. Sustained winds will keep conditions touchy on Monday.

Summary

Confidence

Moderate -

Weather Forecast

Monday: Mainly cloudy with no new snow. Winds moderate to strong from the northwest. Freezing level to 300 metres with alpine temperatures of -7. Tuesday: Sunny with cloudy periods. Winds light to moderate from the northeast. Freezing level returning to valley bottom with alpine temperatures of -8. Wednesday: Sunny. Winds light to moderate from the northeast. Alpine temperatures to -8 with a possible temperature inversion bringing temperatures closer to -4.

Avalanche Summary

Although the storm obscured visibility of most higher elevation terrain, a number of observations of a natural avalanche cycle took place from lower elevations on Saturday. Alpine and treeline features were observed running to Size 3.5 while warm and quickly consolidating storm snow below treeline promoted both storm slab and glide avalanche activity to Size 2. Numerous loose wet avalanches have also been reported at highway elevations over the past two days. It remains to be seen to what extent avalanche activity has involved deeper persistent weaknesses, but at least two larger (Size 3-3.5) avalanches were reported failing at ground level up in the Ningunsaw area. Sustained strong winds and a changing wind direction can be expected to promote ongoing natural avalanche activity over the short term.

Snowpack Summary

A storm that impacted the region over Friday to Sunday morning has delivered approximately 60-110 cm of new snow to the mountains, with the greatest depths accumulating in coastal areas. Strong to extreme southwesterly winds accompanied the storm while lower elevations saw precipitation falling as rain. As of now we can 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 activity has captured our attention, there continue to be several other surface hoar layers of concern from early January and Christmas. Some reports have shown these persistent weak layers to be rounding and bonding, however recent reports have shown sudden planar releases in snowpack tests with hard forces applied. The heavy precipitation has been a good test for these older buried weak layers and observations over the next couple of days should reveal to what extent they have been involved in avalanche activity.

Problems

Storm Slabs

An icon showing Storm Slabs
Ongoing strong winds will keep our fresh storm slabs touchy over the short term. Stick to supported low angle terrain while the storm snow stabilizes and maintain constant awareness of overhead hazards.
If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.The new snow will require several days to settle and stabilize.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

2 - 4

Persistent Slabs

An icon showing Persistent Slabs
Recent loading likely cleaned out some slopes that have been harbouring persistent weaknesses, but it may still be possible to trigger large avalanches on deeply buried weak layers. Storm slabs may also be capable of 'stepping down' to these layers.
Avoid areas with overhead hazard.Be aware of the potential for wide propagations due to the presence of buried surface hoar layers.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 4

Valid until: Jan 30th, 2017 2:00PM