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Avalanche Forecast

Archived

Nov 29th, 2012–Nov 30th, 2012

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

Regions

South Rockies.

The timing of this storm is suspect. If you are seeing more precipitation than forecast in your area on Friday, then consider these danger ratings to be a bit low.

Confidence

Fair - Due to limited field observations for the entire period

Weather Forecast

Overnight Thursday: Freezing levels are expected to continue to rise on Thursday evening up to about 1600 metres and should be combined with moderate SW winds and light precipitation. During the overnight period, expect freezing levels to move down to about 1200 metres combined with continued moderate SW winds and precipitation increasing to moderate ( 10-15 mm for the Fernie Area, and about 10 mm further East). Friday: Freezing levels should rise a little bit during the day as waves of light to moderate precipitation continue ( 5-10 mm total during the day). SW winds are expected to continue in the alpine.Saturday: The freezing level should start to drop down to near the valley bottoms after a cold front moves through to the East. Alpine winds should continue to be moderate from the SW. Poor confidence in precipitation amounts and timing for Saturday and Sunday.

Avalanche Summary

No recent avalanche observations.

Snowpack Summary

Surface conditions vary throughout the region. You might find surface hoar, a light zipper crust or something entirely different depending on what drainage you're in.  You need to know what the weekends snow is falling on before committing to a line.  Start by going small this weekend & remember that the storm slab has the potential to behave in very different manors depending on what aspect & drainage you're in.  This is a very young snowpack, don't take your eyes off it.  Alpine snow depths are somewhere between 1 - 2 m. Depths quickly drop below threshold near treeline. An early season rain crust exists from rain events in late Oct./early Nov. Wind exposed terrain at and above treeline features old isolated wind slabs that range from 50 - 100 cm in depth.

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.