Avalanche Forecast

Issued: Dec 3rd, 2013 8:39AM

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.

jlammers, Avalanche Canada

South Columbia.

Summary

Confidence

Fair - Wind effect is extremely variable

Weather Forecast

Cold and mostly clear skies are expected for the forecast period as a dry arctic air mass becomes firmly embedded over British Columbia. Ridgetop temperatures are expected to hover around -16 on Wednesday and Thursday, and then drop to about -20 on Friday. Expect periods of moderate north/northeasterly winds.

Avalanche Summary

On Monday 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. On Tuesday, numerous size 2 natural wind and storm slab avalanches were observed in Glacier National Park along the highway corridor. I would expect similar conditions throughout the South Columbia Region.

Snowpack Summary

A potent storm slab now exists throughout the region and is ripe for rider triggering at all elevation bands. In deeper snowpack areas this new slab is about 60cm deep and 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 with potential for large and destructive avalanches. To add to the complexity of the current scenario, east/northeasterly winds are responsible for new windslabs on south and west facing terrain.In the mid snowpack you may find a layer of surface hoar or a 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. A conservative and investigative approach is required for safe mountain travel.

The new snow will require several days to settle and stabilize.>Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 5

Wind Slabs

Strong northeasterly winds have redistributed loose surface snow into reactive wind slabs on southwest facing terrain. This is an atypical loading pattern which has the potential to catch skiers/riders by surprise.

Be cautious as you transition into wind affected terrain.>Avoid travelling in areas that have been reverse loaded by winds.>

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

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

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

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Valid until: Dec 4th, 2013 2:00PM