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Avalanche Forecast

Archived

Jan 24th, 2013–Jan 25th, 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

Poor - Intensity of incoming weather is uncertain

Weather Forecast

Thursday night and Friday: Another frontal system is moving inland from the coast. Light precipitation expected to start overnight and go until the afternoon Friday for a total of 5-10 mm. in the wettest zones. Winds are expected to be strong from the SW-W in the alpine and temperatures remaining cool (-7 C) and freezing level staying at the surface. Saturday: Trace to light precipitation amounts, lighter W winds and similar temperatures. Sunday: Similar unsettled conditions providing trace to light precipitation, cool temperatures with light SW winds.

Avalanche Summary

No recent natural avalanche was reported. An explosive shot resulted in a size 2 slab on a W slope which is suspected to have run on the early January weak surface.

Snowpack Summary

More snow will add on to the 10 cm that fell yesterday with moderate winds from the W-SW. New windslabs in the alpine and at treeline under lee ridgetops will form and their bond to the old surfaces might be weak for a certain time. Loose snow is expected to slide very easily on the January 23th surface hoar layer that is located in shaded-sheltered areas below treeline and also on the buried suncrust found on South facing slopes. The early January surface hoar weak layer is still a concern to professionals. It is mostly found under 30-50 cm in the below treeline band and is still producing a variety of test results. Under these concerning layers, a strong mid-pack overlies a weak facet/crust layer near the base of the snowpack, which is now considered inactive.

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.