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Avalanche Forecast

Jan 3rd, 2015–Jan 4th, 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
2: Moderate
The avalanche danger rating below treeline will be moderate
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
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: Purcells.

The new storm in the forecast is expected to drive avalanche danger up to HIGH over the next few days.

Confidence

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

Weather Forecast

Cold arctic air is expected to persist overnight bringing alpine temperatures down to about -20 in the North of the region. Flurries are expected overnight with only a couple of cm accumulation, and another 2-3 cm during the day on Sunday. Snow beginning Sunday evening as the Southwest winds increase to moderate and the new storm moves into the region. Expect 5-10 cm of dry new snow by Monday morning, and another 5-15 cm during the day as Westerly winds increase to strong. Alpine temperatures are expected to gradually increase with highs of about -8 by Tuesday. The storm should continue on Tuesday with another 5-15 cm. Snowfall amounts are difficult to forecast due to the moist air moving in from the Southwest colliding with the cold air from the Northeast.

Avalanche Summary

Natural and sled triggered avalanches were reported up to size 1.5 in pockets of cross-loaded windslab in the alpine on West thru Northwest aspects. The mid-December persistent weak layer continues to be a concern for human triggered avalanches.

Snowpack Summary

New snow and moderate Southwest winds developed isolated pockets of touchy windslab in the alpine and at treeline. Since previous winds were from the north or northwest, wind slabs should be suspected on a wide variety of aspects in exposed terrain. A thin layer of surface hoar with variable distribution was buried on December 27th by about 5-10 cm of light dry snow. As more snow accumulates, this interface could become one to watch. Deeper, at about 40-60 cm below the surface, a persistent crust/surface hoar layer from mid-December can be found. Recent snowpack tests show moderate "pops"-type results on this layer, indicating the potential for avalanches to propagate if triggered on this layer. This persistent slab problem is reasonably widespread across the region and is not expected to improve quickly. A deeper crust/facet layer which formed early in the season may still be triggerable from thin or rocky snowpack areas.

Avalanche Problems

Persistent Slabs

The mid-December persistent weak layer of surface hoar and crust continues to be a concern for human triggering. This weak layer has a variable distribution across the region. Dig down and find out if you have this layer and how it reacts in tests.
Choose well supported terrain without convexities.>Stick to small features with limited consequence and be aware of what is above you at all times.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 2 - 5

Storm Slabs

New storm slabs are expected to develop with forecast new and wind. Old windslabs may continue to be triggered in isolated locations in the alpine and at treeline.
The recent snow may now be hiding windslabs that were easily visible before the snow fell.>Give cornices a wide berth when travelling on or below ridges.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 3