Archived

Avalanche Forecast

Feb 16th, 2013–Feb 17th, 2013

Alpine

4: High

The avalanche danger rating in the alpine will be high

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

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

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: South Columbia.

The last storm was very reactive, and now the new storm is adding to the load above the same weak layer. I suggest conservative goals and a day of watching what happens from safe lines.

Confidence

Fair - Forecast snowfall amounts are uncertain on Sunday

Weather Forecast

Overnight and Sunday: Snow fall is expected to continue into the night and then taper off by late morning. Expect 20-30 cms total at treeline with moderate West winds and strong gusts during the snow fall. A weak ridge of high pressure is expected to fill in behind the trough, shifting the winds to moderate Northerly with strong gusts.Monday: The weak ridge is expected to flatten out and let the next trough move inland from the coast. Expect mainly cloudy skies and light precipitation with light Westerly winds and the freezing level rising up to about 1000 metres.Tuesday: The next weak trough is expected to bring another pulse of precipitation to the region, combined with light West winds and slightly cooler temperatures.

Avalanche Summary

Reports suggest that the recent storm slab settled under warm temperatures and continued to be reactive to ski cuts. There were several accidental releases in the storm slab up to size 1.5 that were about 20 cms deep. There were some natural avalanches from steep mid elevation paths along the highway corridor. There was one natural cornice release that stepped down to the January 23rd layer that was down about 80 cms and was reported to be size 2.5.

Snowpack Summary

New snow is adding to the recent storm slab that is between 15-30 cms across the region. This new load is expected to create another cycle of wind slab releases in the alpine and treeline, and may cause the recent storm slab to become more reactive where it is sitting on the weak surface hoar layer that was buried on February 12th. The recent storm slab has also been reactive on Southerly aspects where a sun crust formed during the period from February 8th-11th. Loading on the recent storm may cause another cycle of natural activity, or an increased sensitivity to human triggers. There are older weak layers that are now buried down around 70-80 cms and also at about 110 cms. These layers have been unlikely to trigger by skiers, but they may still be sensitive to large loads like avalanches in motion or cornice fall.

Avalanche Problems

Storm Slabs

New snow is adding to the load of the recent storm slab above the buried crusts, wind slabs, and weak surface hoar crystals. This new slab may be very easy to trigger on steep rolls and unsupported terrain features.

The new snow will require several days to settle and stabilize.>Choose conservative lines and watch for clues of instability.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 5

Wind Slabs

Forecast snow and Westerly winds are expected to develop new wind slabs in the alpine and at treeline. Recent wind slabs may not be well bonded and may difficult to locate due to the new snow.

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 5

Persistent Slabs

There are older layers of buried surface hoar and crusts that are unlikely to be triggered by the weight of a skier or sledder, but may be triggered by large additional loads like cornice fall or wind/storm slab avalanches in motion.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>Avoid open slopes and convex rolls where buried surface hoar may be preserved.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 2 - 6