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Avalanche Forecast

Archived

Jan 25th, 2013–Jan 26th, 2013

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

Regions

Purcells.

Confidence

Fair - Wind speed or direction are uncertain on Saturday

Weather Forecast

Friday night and Saturday: A bit of a precipitation break with moderate winds with strong gusts from the NW friday night. Another unsettled air mass will bring more precipitation on the region on Saturday but no significant amounts. Light W winds gusting moderate in the afternoon and surface freezing level and seasonal temperatures in the alpine (-7 C). Sunday: Similar pattern with some light precipitation, moderate W winds, cooler temperatures (down to -12 C). Monday: Arctic front tracking towards the region bringing more light precipitations and even cooler temperatures.

Avalanche Summary

Small loose avalanche cycle up to 1.5 ran on the January 23rd interface mostly on NE aspects. There was also a few small skier triggered avalanches also on NE aspects.

Snowpack Summary

Around 20 cm fell with the last 2 systems (more in the S and W and less in other parts of the region) with light to moderate S-SW winds creating soft slabs in the alpine and at treeline below ridgetops. It is expected that the bond between these slabs and the underlying surface will improve, however they will also gain propagation potential with the continuing settlement and forecasted moderate winds. In other words, they could be harder to trigger, but if triggered, they will generate bigger avalanches. The new snow is also sitting on a couple of weak layers; a suncrust on S facing slopes and on a surface hoar layer mostly found below treeline. The bond of the new snow with these type of layers usually takes longer to improve and is harder to predict. It is therefore important to keep monitoring their location and reactivity to ski and snowpack tests. The early January surface hoar layer down 40-60 cm also in the below treeline band is still a concern to professionals. It has been producing a variety of snowpack results but has not been reactive to skier traffic in a while.

Problems

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.