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Avalanche Forecast

Archived

Jan 25th, 2012–Jan 26th, 2012

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Purcells.

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.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.