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Avalanche Forecast

Archived

Feb 15th, 2013–Feb 16th, 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 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.

Regions

South Columbia.

Forecast new snow is expected to add a new load above the recent storm snow that may cause the buried February 12th weak layer to continue to be reactive.

Confidence

Fair - Forecast snowfall amounts are uncertain on Saturday

Weather Forecast

Overnight and Saturday: Moderate Westerly winds are expected as the ridge of high pressure flattens and a trough moves into the interior from the Northwest. Alpine temperatures should stay a few degrees warmer than seasonal overnight as the warm front delivers 5-10 cms. Moderate snow fall should start sometime in the early afternoon when the trailing cold front moves across the region. Expect 10-15 cms with cooler temperatures and gusty West winds.Sunday: Unsettled cool air will be left behind as the next ridge of high pressure builds over the interior. Expect light Northerly winds and alpine temperatures down to about -10.0.Monday: Mainly cloudy as the weak ridge of high pressure moves to the East.

Avalanche Summary

The storm slab continued to be reactive on Thursday. Skiers controlled avalanches up to size 1.5 and  accidentally released avalanches up to size 2.0. Explosives control in the highway corridor resulted in avalanches up to size 2.5 on North aspects at 2000 metres. There were also a couple of natural cornice falls up to size 2.0

Snowpack Summary

There is a lot of variability in the depth of the new snow slab and the new wind slabs. Areas that received 30-40 cms of new snow have developed thick new wind slabs at higher elevations that may be triggered by light additional loads. The storm slab in these areas has been reported to be reactive to skiers, as it slides easily on a layer of surface hoar that developed just previous to the latest storm. In some areas there is a sun crust that developed during the sunny weather last weekend that is a smooth and fast sliding layer for the new storm slab. Deeper weak layers continue to show planar results in snow profile tests down about 70 cms and also at about 100 cms. These deeper layers are less likely to be triggered by skiers, but cornice falls or other large triggers may step down and result in 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.

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.