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Avalanche Forecast

Feb 4th, 2015–Feb 5th, 2015
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
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
4: High
The avalanche danger rating at treeline will be high
Below Treeline
4: High
The avalanche danger rating below treeline will be high
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

Regions: South Columbia.

If more snow than forecast arrives during the day on Thursday, avalanche danger may reach HIGH.

Confidence

Fair - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

Snow starting overnight or early Thursday morning combined with strong Southwest winds and alpine temperatures near -5. Expect 10-20 cm by early afternoon on Thursday and another 10-15 cm overnight by Friday morning. Strong Southwest winds on Thursday becoming very strong Southerly on Friday as warm Pacific air is pushed up and over the cold arctic air to the North. The North and East of the region may see enhanced snow fall due to the cooling effect of the arctic air. The South and West of the region may see freezing levels rise up to 2000 metres that may result in rain up to treeline elevations. The storm should continue on Saturday with another pulse (15-25 cm) of warm and moist air pushed by moderate Southwest winds.

Avalanche Summary

There were numerous size 1.5 natural and skier triggered avalanches reported from Tuesday. In some areas pockets of wind transported snow were easy to trigger up to size 1.5 at ridgetops where they were sitting on a hard crust. I suspect continued loading from the forecast snow and wind over the next few days may result in widespread natural activity within the storm slab, or on the crust that was buried at the end of January. Storm slab avalanches in motion may result in persistent weak layer avalanches which may be large and destructive.

Snowpack Summary

Thin new slabs may not be bonding well within the storm snow. Pockets of wind transported snow at ridgetops may be easy to trigger where they are sitting on the crust that formed last week. The new storm slab is up to 40 cm thick and sits above a variety of old surfaces. The old surfaces include the crust that formed last week, a new layer of surface hoar that developed during the clear weather late last week, and in some places wind slabs that developed smooth hard surfaces. Deeper in the snowpack the mid-January surface hoar remains a concern. It can be found down 60-120 cm across the region, but in most places it is about one metre down. In some locations it has reportedly gained quite a bit of strength, but elsewhere it is still producing sudden collapse (popping) failures in snowpack tests. The mid-December surface hoar layer is now 80 to 140cm below the surface and has become unlikely to fail, the storm at the end of the week should be a good test to see if it will become active again.

Avalanche Problems

Storm Slabs

Forecast new snow and wind are expected to result in natural avalanches releasing within the storm slab, or on the buried crust. Incremental loading from several pulses of moisture may make it difficult to forecast the timing of natural avalanches.
Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>Be cautious as you transition into wind affected terrain.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 4

Persistent Slabs

Buried persistent weak layers may be over-loaded by the forecast new storm snow resulting in human triggering, or storm slab avalanches in motion stepping down to the deeply buried weak layers.
Be aware of thin areas that may propagate to deeper instabilities.>Choose well supported terrain without convexities.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 2 - 5