Bulletin d’avalanche

South Columbia

Dec 1 – 2, 2011Avalanche Canada
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Archivé · expiré 15 years ago

Danger d’avalanche

Sat
Sun
Alpin
3 · Marqué
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely - Very Likely
    Taille
    1–5
    South winds last weekend combined with North winds midweek have created hard and soft windslabs at & above treeline that are easily triggered.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–6
    It's getting harder to trigger but this layer can still produce destructive avalanches. Avoid thin rocky locations where there isn't much snow between you and this sleeping dragon & remember smaller avalanches could step down & trigger this layer.

Confidence

Fair - Due to limited field observations

Weather Forecast

Friday: A cold front sweeps across the region Thursday night lingering into the first half of Friday bringing light precipitation & big winds out of the NW clocking in at 60 - 90 km/h. No significant precipitation is expected out of the system. Temps are forecasted to stay steady around -6 @ 1500m on Friday.Saturday: High pressure builds back into the region Saturday keeping the region dry through the weekend under scattered clouds. Freezing levels will stay near valley bottom but an inversion is forecasted for the area bringing above freezing temperatures between 1800m & 2300m Sunday & Monday.

Avalanche Summary

Soft slabs at and above treeline are being easily triggered in wind affected areas.

Snowpack Summary

Heading into the weekend the big thing to look for is windslabs at and above treeline. Last weekend's 40 -60 cm's accompanied by strong southwest winds loaded north - east facing aspects. Since midday Wednesday the region has been under the effect of dry northwesterly flow. Strong winds blowing out of the N - NW have loaded up the south - east facing aspects. We call this reverse loading. The take home point is this: Wind slabs can be found on all aspects at and above treeline. Clear skies this weekend are going to lure folks up into the alpine. Those headed up high will need to plan their routes carefully to avoid getting into a tangle with a windslab. You can avoid windslabs and find the best riding in more sheltered locations. Last weekend's warm storm deposited 40-60cm's of snow which has been pretty heavy at all but the highest alpine elevations as freezing levels rose to 1800m under the strong southwest flow. Mild temperatures combined with this new load are promoting bonding & settling of the snowpack. On Sunday Nov. 27th this warm system created a rain crust that is present at and below 1500m. 10 - 30 cm of snow are now on top of this crust. We'll need to watch for faceting above and below this crust as we move forward.The snow depth is currently 200 - 250cm in the alpine. An early November surface hoar layer is buried around 150cm down. Triggering this layer is difficult. But, test results continue to show sudden planer shears meaning that this layer has some energy in it. This is the classic low probability/high consequence avalanche problem. Mid-November storms produced a widespread avalanche cycle on this layer.On Thursday Nov. 24th we received reports from the Southern Selkirks of a widespread avalanche cycle. Large avalanches released near the ground on several aspects. The majority of these observations were from north through east facing slopes. This was likely the result of an early season rain crust that until last week was bridging over weak basal facets at the ground. Last weekend's storms pushed it to the breaking point resulting in an avalanche cycle. Very little is known about this rain crust, especially when it comes to distribution. Is it limited to the Southern Selkirks, or is it more widespread?

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