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Archived

Avalanche Forecast

Dec 12th, 2018–Dec 13th, 2018
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
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low

Regions: Lizard-Flathead.

Wednesday was a day of very active avalanche conditions. A bit more snow and a lot more wind in the forecast means storm slabs will remain primed for human triggering.

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

Wednesday night: Increasing cloud and flurries bringing a trace to 5 cm of new snow. Strong southwest winds.Thursday: Cloudy with continuing flurries bringing about 10 cm of new snow. Moderate to strong southwest winds. Alpine high temperatures around -6, increasing overnight as freezing levels rise to 2000 metres.Friday: Mainly sunny with increasing cloud and light flurries in the evening. Strong to extreme southwest winds. Alpine high temperatures to about 0 as freezing levels rise to 2200 metres.Saturday: A mix of sun and cloud with easing flurries a trace of new snow. Strong to extreme southwest winds easing in the afternoon. Alpine high temperatures around -5 with freezing levels returning to about 1500 metres.

Avalanche Summary

Reports from the Fernie and Corbin areas on Wednesday showed numerous storm slab releases, both natural and explosives-triggered. Slabs ranged from 20-80 cm in depth, depending on wind effect, with sizes generally from size 1.5-2. Size 2 would be classified as 'large'. These all occurred from about 1700-2000 metres and were focused on north to east aspects due to strong southwest winds.Another recent notable avalanche was a size 2 human triggered avalanche on December 2nd in Cornice Bowl north of Fernie. It occurred on a northwest facing feature at 2300 m and ran on a crust layer. There are good photos in this MIN report.

Snowpack Summary

Tuesday night's storm brought 30-40 cm of new snow to the region. The new snow has buried an old snow surface that was noted earlier in the week for a cover of large, weak surface hoar crystals as well as hard wind slab and some sun crusts. Beneath the new snow and old surface, the snowpack has been stuck in early season conditions, hovering at roughly 100 cm of depth in alpine areas and much less at lower elevations. See the snow profile in our field team's MIN report for a visual representation of the pre-storm snowpack here. Aside from storm slabs now blanketing the surface, a primary concern is the combination of weak facets and crusts in the bottom half of the snowpack. The crust is most prevalent at and above treeline and is likely most problematic on north-facing features, especially those that are large and planar in nature. A layer of large surface hoar can also be found at similar depths in some areas, as found in a recent MIN report here.

Avalanche Problems

Storm Slabs

More forecast snowfall and wind are expected to feed our storm slab problem. Strong winds are the most problematic factor with their increased capacity for loading lee slopes and speeding slab formation.
If triggered, storm slabs may step down to deeper layers and result in large avalanches.Be alert to conditions that change with elevation, aspect and exposure to wind.Use ridges or ribs to avoid pockets of wind loaded snow.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 2

Deep Persistent Slabs

The weak structure of our lower snowpack is being tested by loading from snowfall and wind. Be especially cautious around alpine areas that form deep wind deposits. Storm slab releases that 'step down' could produce very large avalanches.
Back off if you encounter signs of instability like whumphing, shooting cracks or recent avalanches.Avoid shallow, rocky areas where the snowpack transitions from thick to thin.Be especially cautious as you transition into wind affected terrain.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 1 - 2