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Archived

Avalanche Forecast

Feb 5th, 2015–Feb 6th, 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: Glacier.

As the storm hits, heavy snowfall and strong winds will rapidly load an already touchy snowpack. Avoid exposure to avalanche terrain. Travel in areas exposed to run-outs is not recommended; large avalanches are expected to run to valley bottom.

Weather Forecast

Another intense storm is beginning. 20-30cm of snow are expected by tomorrow morning, with freezing levels rising to 1700m. Winds will increase from light to strong as the storm progresses. Heavy precip will continue on Friday, with another 30cm of snow, freezing levels at 1800m, and sustained winds. Another 15cm is expected on Saturday.

Snowpack Summary

The Jan 30 surface hoar/crust layer, which exists up to 2200m, is down 30-50cm. Snowpack tests indicate that the storm slab may bond poorly to the crust, which acts as a smooth bed surface. Windloading will increase slab properties in lee areas. Jan 15 surface hoar layer is down 70-110cm and tests indicate it is still reactive in some areas.

Avalanche Summary

Light winds and flurries didn't add enough load to trigger many avalanches yesterday. There were a few natural avalanches to size 2 observed. Small slabs triggered by skiers indicated that the slab is forming. On Tuesday skiers accidentally triggered a size 2.5 avalanche from a SE aspect at 2120m. The avalanche propagated ~200m wide and ran ~600m.

Confidence

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

Avalanche Problems

Storm Slabs

A soft slab is forming which sits on a firm bed surface. This storm slab is triggerable and may propagate widely due to buried surface hoar on a crust. Continued loading through the storm will increase reactivity and the size of resulting avalanches. 
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 - 3

Persistent Slabs

The January 15 surface hoar layer buried down 70-110cm is still reactive in many areas. Rapid loading over the next few days may overload it, or storm slab avalanches may step down to this layer.
If triggered the storm slabs may step down to deeper layers resulting in large avalanches.Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 3 - 4