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Archived

Avalanche Forecast

Jan 28th, 2017–Jan 29th, 2017
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
4: High
The avalanche danger rating at treeline will be high
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Northwest Coastal.

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

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.

Avalanche Problems

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

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