Bulletin d’avalanche

Purcells

Jan 25 – 26, 2012Avalanche Canada
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Archivé · expiré 15 years ago

Danger d’avalanche

Fri
Sat
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    2–6
    Tuesday night’s storm was accompanied by big winds out of the S, SW. Expect deep and potentially sensitive wind slabs in wind exposed terrain.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    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

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–5
    30 - 40 cm of snow fell tues eve forming a cohesive slab at all elevations. Avalanches triggered in the storm snow could step down to a variety of sliding layers creating large un-manageable avalanches. Give the new snow some time to settle out.

Confidence

Fair - Due to variable snopack conditions

Weather Forecast

A weak system will bring a few cm's to the region Wednesday night into Thursday morning. High pressure then works its way up from the States which will keep things fairly dry Thursday afternoon into Friday. There will be broken clouds as NW flow remains aloft, the occasional flurry may even develop, but we shouldn't see any significant accumulations. Winds will ease up a bit Thursday, but they will still be strong out of the NW at ridgetop. @ 1500m expect a daytime high of -3 with an overnight low of -7 Thursday.

Avalanche Summary

A couple of large natural avalanches in the alpine (to size 3) were reported on NE and SE- E aspects in the Dogtooth range Wednesday. Smaller avalanches of the loose snow & soft slab variety (to size 1.5) were also reported running in the new/old snow interface. Elsewhere in the region a natural avalanche that started in steep un-skiable terrain was observed. All the reported avalanches were running fast and entraining snow as they ran down the slope.

Snowpack Summary

The Purcell’s are one of the more complex snowpacks in the province right now.Tuesday night the region received 30 – 40 cm of new snow accompanied by strong winds out of the SW. Just a few days ago the region received 20 – 40 cm with S & SE winds. A test profile on Tuesday revealed a sudden planer shear down 40 cm failing on surface hoar with a hard trigger. That was before the storm, that layer now has 70+ cm of snow on it and is likely more sensitive. Resistant shears were noted in last weekend’s storm snow yesterday too. The bottom line is that there are a number of different weaknesses/sliding layers in the snowpack which are now under additional strain.The mid-December surface hoar/facet persistent weakness, now down around 70cm on the eastern side of the range and as deep as 230cm 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.

Régions couvertes