Avalanche Forecast

Issued: Dec 2nd, 2013 8:46AM

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

jlammers, Avalanche Canada

South Columbia.

Summary

Confidence

Good

Weather Forecast

Cold and mostly clear skies are expected for the forecast period as a dry arctic air mass begins to dominate British Columbia. Alpine temperatures are expected to hover around -18.0 with periods of moderate to strong northerly winds.

Avalanche Summary

Due to inclement weather, observations have been limited; however, a size 3 natural slab avalanche was noted in the southwest corner of the region. It occurred on a north/northeast aspect at 2400m. The exact interface is unknown. In the same corner of the region a size 2.5 slab avalanche was observed releasing on a south facing slope at about 2100m on the recently buried sun crust.In the northwest of the region, fairly widespread natural slab activity to size 2 was also noted. The most recently buried surface hoar interface was the suspect in these events. I expect to hear about more recent avalanche activity when the skies clear on Tuesday.

Snowpack Summary

A potent storm slab now exists throughout the region and is ripe for rider triggering at all elevation bands. Recent accumulations are likely approaching 70cm in some areas. This new snow covers a complex variety of old surfaces which include melt-freeze crusts on previously sun-exposed slopes and touchy surface hoar crystals in sheltered terrain. These weaknesses are likely to persist for some time after the storm ends with potential for large and destructive avalanches. To add to the complexity of the current scenario, northerly winds have created a reverse loading pattern forming new windslabs on south facing terrain.In the mid snowpack you may find a layer of surface hoar or crust buried in mid-November which sits about 60cm above the ground. Near the base of the snowpack you'll find the October crust/facet combo. The most likely place you'd trigger this layer is on smooth, planar, high north facing slopes, especially if the snowpack is unusually shallow in that area.These persistent layers are slowly becoming more difficult to trigger. However, they have the potential to cause very large and destructive avalanches, and may 'wake-up' with the increased load of the new snow.

Problems

Storm Slabs

This potent new storm slab will be tricky to manage as it overlies a variety of weak surfaces. The new snow may also exist as a windslab in exposed terrain. Expect touchy conditions for the forecast period.

Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>The new snow will require several days to settle and stabilize.>Avoid travelling in areas that have been reverse loaded by winds.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 5

Persistent Slabs

Loading from the recent storm may reactivate persistent weaknesses buried in the mid and lower snowpack. If triggered, avalanches on these layers would be large and destructive.

Be aware of the potential for large, deep avalanches due to the presence of buried persistent weaknesses.>Caution around large unsupported slopes and areas with a thin or variable snowpack. Persistent slabs have the potential for wide propagation.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Valid until: Dec 3rd, 2013 2:00PM