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Avalanche Forecast

Archived

Feb 17th, 2013–Feb 18th, 2013

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

Regions

South Columbia.

Confidence

Fair - Due to variable snowpack conditions for the entire period

Weather Forecast

Overnight and Monday: A weak ridge of high pressure is expected to give clear skies, light winds, and alpine temperatures dropping down to about -10.0 overnight. The ridge should continue to dominate on Monday bringing mostly clear skies with some valley cloud. The next trough is expected to move across the interior on Monday afternoon or evening bringing high cloud and a chance of light precipitation.Tuesday: Mostly cloudy with a chance of light precipitation and light winds.Wednesday :Another weak ridge is expected to fill in behind the trough, bringing light winds and cloudy skies in the morning. Broken skies and continued clearing in the afternoon.

Avalanche Summary

Skiers continued to release avalanches in the storm snow up to size 2.0 and natural avalanches were reported up to size 3.0 along the highway corridor.

Snowpack Summary

New snow has added to the recent storm slab above the February 12th weak surface hoar layer. This layer is now buried down about 20-50 cms depending on where you are in the region. This variable storm slab is also above a sun crust on Southerly aspects. New wind slabs developed at higher elevations due to the new snow and wind during the storm. These soft new wind slabs may be hiding stiffer wind slabs that are a couple of days older. Deeper persistent weak layers from early February and late January continue to show planar failures when moderate to hard forces are applied to snow profile tests. These deeper layers have not been reactive to the loads associated with recreationalists, but they may be triggered by large loads like an avalanche in motion, or a cornice fall.

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.