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Avalanche Forecast

Mar 11th, 2013–Mar 12th, 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
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
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: South Columbia.

A warm and wet storm is developing. Strong winds, a heavy storm load, and rising temperatures are increasing the avalanche danger.

Confidence

Fair - Forecast snowfall amounts are uncertain on Tuesday

Weather Forecast

Overnight and Tuesday:  A warm front is forecast to move into the interior overnight bringing cloud and strong Westerly winds. Moderate snow fall amounts are expected to begin by early morning and become heavy during the day. Freezing levels are expected to rise to about 1200 metres.Wednesday:  Continued warm and wet. Moderate to heavy precipitation with strong Westerly winds and freezing levels rising to about 1500 metres.Thursday: Unsettled weather with continued light to moderate precipitation and moderate Westerly winds.

Avalanche Summary

Some thin new pockets of wind slab were released from ski cutting or accidentally while skiing. There was one report of a size 2.5 natural slab avalanche on a West aspect in the Selkirks at 2200 metres. This avalanche was interesting because it failed on a planar slope that had previously released from higher on the slope during the last storm. I expect that the new storm will continue to trigger the deep weak February 12th layer in isolated areas with the right combination of preserved surface hoar, old sun crusts, where no avalanches released after the last storm.

Snowpack Summary

New wind slabs are developing above a new surface hoar layer on shaded aspects and a sun crust on solar aspects. The weak layer of surface hoar that was buried on February 12th is now down about 100-150 cm and was not triggered by cornice falls over the weekend. Some areas report that the February 12th surface hoar is rounding and getting harder to shear in snow profile tests, but continues to give planar shears when it does fail. Avalanches failing on the February 12th layer have become a low probability/ high consequence situation.

Avalanche Problems

Storm Slabs

A new storm slab is expected to develop due to forecast new snow and wind. This new storm slab may be sitting on a weak layer of surface hoar that developed during the recent clear weather.
The new snow will require several days to settle and stabilize.>Avoid freshly wind loaded features.>Be cautious as you transition into wind affected terrain.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible - Likely

Expected Size: 2 - 5

Persistent Slabs

A weak layer of buried surface hoar down about 100-150 cm may be triggered by the load of new storm snow and wind.
Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 4 - 7