Avalanche forecast

Purcells

Jan 23 – 24, 2012Avalanche Canada
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Archived · expired 15 years ago

Avalanche danger

Wed
Thu
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 in the Alpine Tuesday. Expect sensitive & 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 very heavy load (cornice fall, airborne sled). Avalanches could be large.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–5
    Storm slabs have evolved; particularly on the west side of the range with warmer new snow over top of loose dry snow. Watch for storm slab avalanches, especially in steep or convex terrain.

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain on Tuesday

Weather Forecast

A strong westerly flow is setting up for Tuesday with average seasonal temps. The big story is the wind. Winds are forecasted to be out of the W in excess of 100 km/h at ridgetop all day Tuesday. Precipitation will begin to fall Tuesday afternoon continuing into the night, there should be 15 - 20 cm of new snow out of this pulse by Wednesday morning. A second system of lesser intensity moves through the area Wednesday/Thursday producing around 10 cm of snow. Thursday afternoon and Friday look to be generally dry.

Avalanche Summary

Explosive work in the region Sunday produced avalanches to size 3. The bulk of this activity was on slopes facing E and N. Observers noted a widespread cycle in the storm snow affecting both the alpine & treeline elevation bands over the weekend on all aspects.

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.

Regions covered