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Avalanche Forecast

Archived

Mar 11th, 2013–Mar 12th, 2013

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

Regions

Kootenay Boundary.

Confidence

Fair - Forecast snowfall amounts are uncertain for the entire period

Weather Forecast

Monday Night and Tuesday: The first of a series of systems approaching the interior is expected to start spreading precipitation over the region early Tuesday. Moderate precipitation amounts (around 15 mm water equivalent) are expected with strong SW winds. Freezing level will start rising to reach around 1700 m. and will stay high for the rest of the period.Wednesday: Precipitation easing off but still some moisture available. Winds are forecasted to be strong to extreme from the W. Temperatures staying warm and freezing rising up to 1900 m.Thursday: Another burst of precipitation (15-20 mm) is expected with similar freezing levels and lighter winds switching from the SW.

Avalanche Summary

There was report of some sluffing in steep terrain up to size 1.5 on shaded aspects. Forecasted weather will probably increase avalanche activity in the days to come.

Snowpack Summary

A trace of new snow overlies a variety of surfaces; a 1-3 cm thick suncrust on SE-S-SW facing slopes all the way up in the alpine, a melt-freeze crust up to 1800 m., a well developed surface hoar on shaded slopes above that elevation and some wind slabs in the alpine on Northerly aspects. The forecasted precipitation and warm temperatures will add a significant load to the snowpack (possibly from 30 to 50 mm in water equivalent until Thursday). I suspect that the variety of surfaces described previously will become gradually more reactive as the load add up starting tomorrow. This could also awake the 60-90 cm deep persistent surface hoar layer that has been less reactive to skier traffic lately creating a potential for very large avalanches.

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.