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Avalanche Forecast

Jan 23rd, 2013–Jan 24th, 2013
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
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
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Purcells.

This forecast is based on the most storm snow amounts (South and West of the region). The rating would be one step too high for areas that do not get significant amounts.

Confidence

Fair - Intensity of incoming weather is uncertain

Weather Forecast

Wednesday night and Thursday: Precipitation tapering off overnight as the system moves across the region. Winds should pick up in the evening to strong speeds from the W and slow down a bit during the day Thursday. Temperatures lowering to around -8 C in the alpine and freezing levels at the surface. Friday:  Another system is approaching which should leave some light precipitation during the day with strong W winds that should ease in the afternoon. Similar temperatures are expected. Saturday: More precipitation, cool temperatures and lighter winds from the W.

Avalanche Summary

A couple natural slab avalanches on S-SW aspects size 2.5 were reported in the Northern part of the region. One would have initiated in a shallow/crossloaded feature and would have stepped down from a 5 cm deep surface hoar instability to a 30 cm deep facet instability and then to the old facet/crust combo at the bottom of the snowpack down 85 cm. A skier triggered size 2 slab avalanche was also reported in the central part of the region which would also have initiated in a cross-loaded feature on a NW aspect. Suspect failure on the January 4th surface hoar down around 40 cm.

Snowpack Summary

The new snow will fall on a variety of surfaces; windslabs in the alpine, facets, surface hoar below treeline in sheltered areas and a suncrust on South facing slopes.  New windslabs and some sluffing in sheltered terrain is expected.  These new layers will most likely be touchy for a certain time.The surface hoar layer below the 40-60 cm of generally well settled snow is still a concern to professionals, especially below 1900 m. in sheltered-shady areas and on S aspects. It still produces sudden planar shears in those areas as well as some resistant planars.  A strong mid-pack overlies a weak facet/crust layer near the base of the snowpack, which is now considered inactive.

Avalanche Problems

Storm Slabs

Storm snow might not bond to a variety of surfaces. New windslabs found on lee side of the forecasted W winds in the alpine and at treeline will most likely be touchy.
Stay off recent wind loaded areas until the slope has had a chance to stabilize.>Avoid areas where sluffing may have severe consequences.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 5

Persistent Slabs

A cautious approach is recommended on steep S slopes and sheltered terrain below treeline.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 2 - 5