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Avalanche Forecast

Dec 30th, 2016–Dec 31st, 2016
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
1: Low
The avalanche danger rating below treeline will be low
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
1: Low
The avalanche danger rating below treeline will be low
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: South Rockies.

The winds will likely drive the avalanche danger over the next day or so. If you see loose snow drifting or getting blown off ridgecrests, expect an increase in wind slab activity.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Saturday: Mix of sun and cloud with light snowfall expected on Saturday night / Moderate westerly winds / Alpine temperatures of -13Sunday: Mix of sun and cloud with light flurries / Moderate northeast winds / Alpine temperatures of -18Monday: Mix of sun and cloud / Strong northeast winds / Alpine temperatures of -20

Avalanche Summary

A large human-triggered avalanche was reported from Corbin yesterday on a wind affected slope in an area where weak facets were present. While technically this area is in the Lizard/Flathead area, I feel as though it is indicative of conditions in the South Rockies region. Where you get a combination of weak sugary snow lower in the snowpack and a supportive upper slab, conditions are ripe for avalanches to be human-triggered at this time. There's lots of loose snow available for redistribution, so if the wind picks up, expect an increase in wind slab avalanche activity.

Snowpack Summary

Up to 20 cm of fresh low density snow has been redistributed by mainly southwesterly winds forming wind slabs in the lee of ridgetops. In general, there is very little structure to the snowpack, with low density new snow sitting over soft, sugary facets. Travel is very challenging as a result. A variable interface that formed during the cold snap in early December can be found buried 30-50 cm deep. This interface consists of weak faceted (sugary) snow and preserved surface hoar in sheltered areas. The interface is likely most reactive in wind-affected terrain where it is covered by hard wind slabs. The snowpack is a generally weak and faceted below this interface, including another weak layer with surface hoar or facets that was buried in early December. Hazards such as stumps, rocks, and open creeks are still a major concern.

Avalanche Problems

Persistent Slabs

Where denser snow overlies weak, sugary snow below, there is the potential to trigger large, dangerous avalanches.
Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.Danger spots are where denser snow overlies weak, sugary snow below.Be aware of the potential for full depth avalanches due to deeply buried weak layers.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 2 - 3

Wind Slabs

Expect fresh wind slabs to form at higher elevations especially if the winds pick up and redistribute loose snow. In shallow snowpack areas, these slabs could pull out to deeper layers below, increasing the severity of an avalanche.
Be cautious as you transition into wind affected terrain.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Avoid freshly wind loaded features.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 2