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Avalanche Forecast

Archived

Feb 25th, 2012–Feb 26th, 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 unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Northwest Coastal.

Confidence

Good

Weather Forecast

Sunday: Mostly sunny, with light northerly winds and temperatures reaching -7. Monday & Tuesday: Expect the clear weather to give way to increasing clouds and flurries, and strong southwesterly winds will ease with the cloud growth. Temperatures should reach -7 in the afternoons.

Avalanche Summary

Natural avalanches up to size 2.0 and rider triggered up to size 1.0 have been reported in the past 24 hrs.

Snowpack Summary

Between 10-25cm of new snow fell in the most recent storm pulse. This adds to the previous storm snow, with 45-60 cm being an average amount over the mid February layers. These layers are a strong melt freeze crust at lower elevations (below 1000m) and wind effected snow higher in the alpine while between these elevations, the interface varies wildly from facets, surface hoar, sun crust or wind press. The surface hoar is not widespread but is responsible for much of the recent avalanche activity. With the additional wind loading, pockets as deep as 90cm are possible on lee features. Recent changes in wind direction have exacerbated the wind slab issue, with slabbing now reacting on south facing terrain features. The mid and lower snowpack is generally well settled and strong.

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.