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Avalanche Forecast

Archived

Mar 10th, 2013–Mar 11th, 2013

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

Regions

Kootenay Boundary.

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain

Weather Forecast

Sunday night and Monday: A quasi-pineapple express is setting over the region that could last till Wednesday. On and off precipitation should start Monday with light to moderate NW winds. Temperatures are forecasted to start to warm up in the alpine (-3 C) and freezing levels to rise to 1300 m.Tuesday: Moderate to heavy precipitation are expected for the region with moderate to strong winds from the SW. Freezing levels rising to 2000 m.Wednesday:  Another frontal system is moving across the region which could give more moderate precipitation and slightly similar mild temperatures but with lighter winds from the same direction.

Avalanche Summary

Widespread natural and skier triggered moist loose avalanche activity on solar aspect up to size 2. There was also report of sluffing on steep northerly aspect.

Snowpack Summary

Recent windslabs have formed on lee features with W and E winds in the alpine and below ridgetops at treeline. These will still be susceptible to sledder and skier triggering. Outside of wind effected areas, I suspect that the top snowpack is generally gaining strength and starting to bond to the underlying surfaces. The 25-30 cm of snow from earlier this week is sitting on an older snow interface above 2000 m. and on a melt freeze crust below that elevation. Up to 80 cm snow overlies a surface hoar and sun crust which is becoming less reactive to skier traffic but that is still a concern to professionals. At the surface, there is a suncrust on SE-S-SW facing slopes all the way up in the alpine, a melt-freeze crust up to 1800 m. and some surface hoar on shaded slopes above that elevation.

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.