Avalanche forecast

South Columbia

Dec 3 – 4, 2013Avalanche Canada
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Avalanche danger

Thu
Fri
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–4
    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.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    3–6
    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

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–5
    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.

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.

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