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Archived

Avalanche Forecast

Jan 27th, 2016–Jan 28th, 2016
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
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
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.

Heavy precipitation will continue to test weak layers and keep the Avalanche Danger HIGH.

Confidence

Moderate - Freezing levels are uncertain on Thursday

Weather Forecast

Up to 30mm of precipitation is forecast for Wednesday night with another 5-10cm of snow expected on Thursday. Ridgetop winds will remain extreme from the southwest while freezing levels will drop throughout the day from 1600m to about 1000m. On Friday and Saturday the region will see light flurries, significantly decreased winds and freezing levels around 700m.

Avalanche Summary

On Tuesday observations were somewhat limited due to weather; however, professional operators in the region were still reporting fairly widespread explosive and naturally triggered storm and persistent slab avalanches to size 2.5. Many of the avalanches were suspected to have failed on the January 9th surface hoar. With the current wet and stormy conditions I suspect further observations will be limited, but we can expect new storm slab activity at elevations where precipitation falls as snow. More importantly, precipitation will add stress to buried persistent weak layers and will increase the likelihood of destructive persistent slab avalanches.

Snowpack Summary

A warm, wet and windy storm is forming dense new storm slabs at higher elevations while rain is saturating surfaces at lower elevations. The January 9th surface hoar/facet layer is down 70-120 cm in most places, and seems most concerning at and below treeline. Around the same depth you may also find a surface hoar/facet interface from around New Years. Ongoing reports of remote triggering, whumpfing, and sudden shears in snowpack tests are all indications that these layers are touchy and could propagate well if triggered. Deeper weaknesses are generally considered to be dormant.

Avalanche Problems

Storm Slabs

Be alert to conditions that change with elevation.>Stay off recent wind loaded areas until the slope has had a chance to stabilize.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely - Very Likely

Expected Size: 1 - 3

Persistent Slabs

A warm, wet and windy storm has overloaded persistent weak layers which lie more than 100cm below the surface. Even if the storm tapers-off on Thursday, I'd give the snowpack a few days to adjust to the new load before pushing into steeper terrain.
Be careful with low angle slopes that may not normally be a concern.>Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 2 - 6