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Avalanche Forecast

Archived

Feb 26th, 2012–Feb 27th, 2012

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

Regions

South Rockies.

Confidence

Fair - Timing or intensity of solar radiation is uncertain on Monday

Weather Forecast

The ridge of high pressure should have moved into the region by Monday morning causing mostly clear skies and cooler overnight temperatures. Strong solar radiation may bring warm temperatures at or above freezing on southerly aspects. Temperatures are expected to drop down to near -14.0 in the alpine Monday night during clear skies and light northerly winds. High pressure should continue for Tuesday, and warm temperatures are expected on sunny alpine slopes. Shaded aspects are expected to remain cool and dry. Some cloud should move into the region by Tuesday evening. Forecast snowfall amounts are unsure for Wednesday at this time.

Avalanche Summary

Natural avalanches have become less frequent, but human triggered avalanches continue to release from light additional loads. The forecast new snow and wind may cause new windslabs that may overload the PWL in some areas.

Snowpack Summary

Moisture in the west of the region collided with cold air in the east and resulted in an intense period of heavy snowfall that was very low density. This new snow should settle with daytime warming and add to the 50-60 cm of recent snow that sits on a highly reactive weak layer of crusts, surface hoar and facets. At 1950 metres elevation we have some snow pack test results from Friday that show that the 40 cm slab of snow above the February 8th weak layer is sliding with easy to moderate forces applied and it is propagating widely with either sudden planar or sudden collapse characteristics. The slab is reported to be less consolidated on northerly aspects than it is on southerly aspects. In areas further north, less snow has fallen on this interface--in the northern Elk Valley for instance, only around 15-20 cm lies above this interface. In lower snow areas, avalanche activity will likely lag behind higher snow areas, except for areas which have seen significant wind transport. In general, the mid-pack is quite strong in most locations. However, lingering concern remains for basal facets, particularly in shallower snowpack areas with steep, rocky start zones.

Problems

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.

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.