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Avalanche Forecast

Dec 22nd, 2016–Dec 23rd, 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
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
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.

Wind slabs continue to be the primary concern throughout the region. In thinner snowpack areas in the southeast, a weakness at the bottom of the snowpack may also be reactive and smaller avalanches have the potential to step down.

Confidence

Moderate -

Weather Forecast

A frontal system is expected to bring snowfall to the region starting Friday morning. 5-10 cm of snowfall is expected on Friday with another 5-10 cm Friday overnight. Alpine winds are forecast to be light from the southeast and treeline temperatures are expected to be around -8C. On Saturday, lingering flurries are expected. Alpine winds are forecast to remain light but shift to a northeast direction and treeline temperatures are expected to be around -12C. On Sunday, mostly sunny conditions are forecast with light alpine wind and treeline temperatures around -15C.

Avalanche Summary

No new avalanches were observed on Wednesday. In the days prior to that, explosives and human-triggered wind slab avalanches have occurred to size 2. In the southeast corner of the region, a few explosive-triggered avalanches have stepped down to deeper faceted layers producing persistent slab avalanches in the size 2.5-3 range. On Friday, wind slabs are expected to be the primary concern resulting from recent strong to extreme southwest winds. There is a bit of uncertainty regarding how the new snow will bond to old surfaces which formed during last week's cold snap. Due to these potentially persistent weak layers, recently formed wind slabs may remain sensitive to human triggering for some time. In the southeast corner of the region, there is concerns for a deep persistent problem. A weakness at the bottom of the snowpack has produced some large avalanches recently. Human triggering may be possible in thin areas or smaller avalanches have the potential to step down to this layer resulting in full depth avalanches.

Snowpack Summary

Since Sunday night, 15-40cm of new snow has fallen. In exposed terrain, strong to extreme winds have redistributed much of this snow into fresh wind slabs. The new snow buries a variable surface that developed over the last week of cold, dry, and windy conditions. This interface consists of scoured surfaces and wind slabs in wind exposed terrain, widespread faceting of the upper snowpack, and surface hoar up to 20 mm in sheltered areas. In sheltered areas, there may be another layer of surface hoar in the upper snowpack which was buried around December 10. Observations have been limited, however, the reports we've received suggest the mid and lower snowpack are somewhat unconsolidated and faceting exists to varying degrees. Below treeline, the snowpack is very shallow and early season hazards such as stumps, rocks, and open creeks are still a major concern.

Avalanche Problems

Wind Slabs

Wind and warming have added cohesion to the recent storm snow, and wind slabs may be ripe for triggering. Use extra caution in steeper, wind-exposed terrain.
Avoid slopes where the snow feels stiff or slabby.Use ridges or ribs to avoid pockets of wind loaded snow.Use caution in lee areas. Recent wind loading has created wind slabs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 2

Persistent Slabs

In thin snowpack areas, a layer of weak snow at the bottom of the snowpack has been reactive recently in the southeast of the region. Triggering may be possible from thin snowpack areas, or smaller avalanches could step down to this layer.
Be aware of the potential for full depth avalanches due to deeply buried weak layers.If triggered, wind slabs may step down to deeper layers resulting in large avalanches.Carefully evaluate and use caution around thin snowpack areas.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 2 - 3