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Avalanche Forecast

Archived

Nov 27th, 2012–Nov 28th, 2012

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

Regions

South Rockies.

This bulletin is based on a very small amount of data. Significant variations in conditions exist.

Confidence

Poor - Due to limited field observations

Weather Forecast

Freezing levels climb to 1500 m Wednesday before dropping back to 1200 m overnight and then stay steady near 1200 m throughout the forecast period.  Expect strong to extreme winds to develop out of the west around lunchtime Wednesday.  These winds should persist throughout the forecast period as a series of low pressure systems cross the province.  The forecast calls for light snowfall beginning in the wee hours of Thursday.  I expect 5 - 10 cm of snow Thursday morning, an additional 5 - 10 cm Thursday night and 5 - 15 cm Friday.  Timing and intensity of the storm should become clearer as the week goes on. 

Avalanche Summary

No recent avalanche observations.

Snowpack Summary

Surface hoar probably blankets many slopes in the region.  It *could* be a problem when it starts snowing later this week.  Alpine snow depths are somewhere between 1 - 2 m.  Depths quickly drop below threshold at and below treeline.  An early season rain crust exists near the ground from rain events in late Oct./early Nov.  Wind exposed terrain at and above treeline likely harbors isolated wind slabs that range from 50 - 100 cm in depth. 

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.