Avalanche forecast

Purcells

Feb 29 – Mar 1, 2012Avalanche Canada
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Avalanche danger

Fri
Sat
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    2–7
    40 -100 cm of storm snow is settling into a cohesive slab above a very sensitive surface hoar layer. While natural activity has dropped off, this layer is still susceptible to human triggering. Avalanches failing on SH will be large & destructive.

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–3
    Loose avalanches failing near the snow surface will continue to be an issue Thursday in steep open terrain as temperature stay cold.

Confidence

Good

Weather Forecast

THUR: A dirty ridge hangs over much of the region today bringing cloudy skies and the occasional convective flurry. I'm only expecting a few cm's Thursday, even in the most favored valleys. The atmosphere stabilizes Thursday evening & 2000m temps drop down to - 16 overnight. FRI: Friday dawns cool & cloudy, but, it is a day of change in the pattern. The ridge flattens late in the day Friday, snow should start up around lunch time & a few cm are expected during daylight hours Friday as the freezing level rises to around 1000m. SAT: There should be around 5 - 10 cm of new when we wake up Saturday morning. (This storm will favor the north half of the forecast region, half the amounts given here if you're headed into the Southern Purcells.) Saturday looks to be a full on storm day, expect another 10 cm during the day. Freezing levels are forecast to rise to 1500m Saturday. SUN: Freezing levels could rise as high as 2000 m Sunday. Sunday also marks the most intense period of snowfall, we should see 15 cm or so in the North & 8 - 10 cm in the South. Snowfall will drop off Sunday evening and we're left with isolated flurries on Monday.2000m Wind:Thur: L, WFri: W, Mod, G StrongSat: W, StrongSun: Strong W, switching Strong SW midday.

Avalanche Summary

Avalanche activity slowed down significantly on Tuesday. There were a few explosive released avalanches to size 2.5 as well as Several loose snow avalanches to size 1 on almost all aspects.

Snowpack Summary

20-25 cm of dry light snow rests above the recent stiff windslabs. The upper snowpack structure is very complex. There are buried layers of surface hoar, buried melt-freeze crusts, and some buried crusts with facets. These weak sliding layers are buried anywhere from 40 - 80 cm by several different storm layers. There are some shears in the storm layers on decomposed and fragmented snow crystals. As the snow above the surface hoar layers settles into a cohesive slab, we are seeing easier and more sudden shears that are a bit deeper. The surface hoar is more likely to produce wider propagations, and lower angle fractures in areas where it is associated with a crust. The crust has been reported to be 2-3 cm thick in some areas. The mid-pack is generally well settled. Basal facets have not been reactive, but operators continue to monitor this layer in tests. Triggering this deep persistent weak layer is unlikely, but shallow snowpack areas or shallow weak areas adjacent to deeper wind loaded slopes are the most suspect locations.

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