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Avalanche Forecast

Archived

Nov 29th, 2017–Nov 30th, 2017

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

Regions

Kananaskis.

Thin areas in the Alpine and at treeline are where you may be able to trigger the persistent slab.  Watch for new windslabs building overnight. 

Confidence

High -

Weather Forecast

Trace amounts of snow are forecast over the next 24hrs.  Temps will be cooler in the -12C range and winds will continue to be strong at Alpine elevations.  Later in the week we may see a few more cm of snow up to 10cm. 

Avalanche Summary

Only one new slab was observed near Mt Lawson, on a NE aspect at 2700m.  The start zone was obscured but it was a sz 2.5 that ran down and into treeline.

Snowpack Summary

5-14cm of snow over the past 24hrs with moderate alpine westerly winds is continuing to build windslabs in alpine areas. Field teams on Wednesday in the Highwood pass area found these slabs 20-30cm thick but they were stubborn to trigger.  Places where we have the most concern for this problem is along ridgelines in immediate lee, cross loaded gullies.  The snow pack is currently fairly complex.  The Nov 26th crust is being found up to 2450m (30cm down), the Nov 23rd crust (down 50cm) up to 2600m and the Halloween crust up to 2600m (down 100cm at treeline).  Hard result were observed in a weak facet layer below the Halloween crust.  Avoid thin areas where you may trigger this weakness. 

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.

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.