Avalanche Forecast

Issued: Feb 16th, 2013 9:42AM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Storm Slabs, Wind Slabs and Persistent Slabs.

triley, Avalanche Canada

Cariboos.

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.

Summary

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 morning. Expect 20-25 cms total at treeline with moderate West winds and strong gusts. A weak ridge should develop behind the storm creating drier conditions with cloudy skies and light North winds. The freezing level should drop down to the valley bottoms tonight and remain there for Sunday.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

There were a few natural cornice falls reported that resulted in avalanches up to size 2.5. No reports of avalanches stepping down below the recent storm slab and surface hoar interface. Expect avalanche activity to increase with the forecast new snow and wind.

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.

Problems

Storm Slabs

The recent storm slab is reported to be settling into a 20-25 cms slab that is variable (soft-stiff) depending on aspect and elevation. The forecast snow and wind are expected to add a new load above this reactive weak layer.

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

Possible - Likely

Expected Size

1 - 5

Wind Slabs

Wind slabs are a couple of days old and reported to be less reactive. Expect new windslabs to develop with the forecast snow.

Avoid freshly wind loaded features.>Be cautious as you transition into wind affected terrain.>Extra caution needed around cornices with current conditions.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

2 - 5

Persistent Slabs

There are older layers of buried surface hoar and crusts that are buried down about 80-110 cms. These layers continue to show results in snow profile tests and may be triggered by large additional loads.

Be aware of thin areas that may propagate to deeper instabilites.>Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Valid until: Feb 17th, 2013 2:00PM