Avalanche forecast

Purcells

Jan 24 – 26, 2012Avalanche Canada
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Archived · expired 15 years ago

Avalanche danger

Thu
Fri
Alpine
4 · High
Treeline
4 · High
Below
3 · Considerable
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Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–6
    Winds in excess of 100 km/h out of the W, SW are expected to accompany the storm Tuesday night into Wednesday. Expect sensitive & potentially deep wind slabs in wind exposed areas.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    4–7
    Two layers to watch: 1. Buried surface hoar, most likely triggered on steep, unsupported slopes amongst the trees. 2. Basal facets, triggerable from thin snowpack areas or by a heavy load (cornice fall, airborne sled). Avalanches could be large.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–5
    15 to 20 cm of snow is expected Tuesday night into Wednesday. Watch for soft slabs in areas exposed to even a small amount of wind.

Confidence

Fair - Intensity of incoming weather is uncertain

Weather Forecast

Tuesday night's storm should deliver 15 - 20 cm of snow by Wednesday morning with the western side of the region picking up the larger amount. The forecast is still calling for big winds in excess of 100 km/h Tuesday night into Wednesday. The freezing level should hover around 1300 m Wednesday with temperatures at 1500 m clocking in at -2. A weak storm system moves into the area Thursday morning producing a few additional cm's before being overtaken by high pressure before lunch. High pressure continues to dominate on Friday.

Avalanche Summary

Natural activity quieted right down on Tuesday & was limited to small avalanches out of steep, rocky unsupported terrain.

Snowpack Summary

The Purcell's are currently quite variable in terms of snowpack. 20 - 40 cm of new snow fell out of the weekend storm & this snow sits on the previous snow surface which consisted of loose dry snow in sheltered areas and old wind slab in exposed areas. Irregular winds out of the SE during the storm created slabs in unusual locations.The mid-December surface hoar/facet persistent weakness, now down around 55cm on the eastern side of the range and as deep as 190cm on the western side, is still causing operators concern, especially in shallow snowpack areas. Recent snowpack tests show moderate to hard, sudden planar results on this layer. The consequences of a failure on this layer would be large. Facets and depth hoar exist at the base of the snowpack. Cornices are large and weak in some areas.Tuesday's wind/storm snow didn't come through as early as I expected, as a result, the danger Tuesday was probably more like Considerable, Considerable, Moderate. For some insight into how this can happen, see the forecasters blog: https://bit.ly/sF10fT

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