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Avalanche Forecast

Nov 27th, 2011–Nov 28th, 2011
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
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
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

Regions: Purcells.

Confidence

Poor - Due to limited field observations

Weather Forecast

The trailing cold front should have moved through the Interior ranges by late Sunday. On Monday a weak ridge of high pressure should bring drier conditions, maybe even some sunshine. It would be nice to get out and see what the last storm brought to the mountains. The weak ridge looks like it will be over-run on Tuesday by a Pacific disturbance that should bring light to moderate precipitation and light northwest winds to all of the interior ranges. Unsettled conditions are forecast to continue on Wednesday, ending sometime Wednesday night or Thursday morning.

Avalanche Summary

Explosive control in the Dogtooth resulted in smaller more stubborn releases to ground up to size 1.5 in the alpine on a north aspect. I suspect that there has been a natural cycle on Sunday when the freezing level was at 1800 metres and the southwest winds were howling.

Snowpack Summary

There is a lot of variation in the snowpack in this region. There is more snow in the Dogtooth area near Golden than there is further south near Invermere and Kimberley. There is probably quite a bit of snow to the west, in areas like the Bugaboos and Jumbo. We don't have any information yet from operators in the west of this region. In the early season we get most of our information from the Dogtooth. We know that there is a weak facetted layer at the ground that has been failing in the last week and resulting in very large avalanches. There has been 60-80 cms recently with strong winds and high freezing levels, creating a cohesive slab above the weak basal layer. In the higher alpine terrain there may be a rain crust from October. The storm and wind-slab instabilities should settle and bond over the next day or two. Any deeper weak layers may continue to be a problem. The danger ratings are steering towards moderate to reflect the storm layers improving. If we see evidence of very large naturals when it clears on Monday, we may change our course!

Avalanche Problems

Wind Slabs

Wind slabs have developed at higher elevations due to wind and snow during the recent storm. Wind-slabs may cause avalanches to step down to the weak layer near the ground.

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood: Likely - Very Likely

Expected Size: 2 - 4

Storm Slabs

Recent storm snow has created a storm slab that is likely to be triggered by skiers and riders. Avalanches started in the storm snow may step down to the weak layers near the ground.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely - Very Likely

Expected Size: 2 - 5

Persistent Slabs

Recent natural and explosive controlled avalanches up to size 3.0 are widespread in the Dogtooth area. Large avalanches should continue to be a concern for human triggers for at least the next few days.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 3 - 6