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Avalanche Forecast

Archived

Mar 8th, 2012–Mar 9th, 2012

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

Regions

Sea To Sky.

Confidence

Fair - Intensity of incoming weather is uncertain for the entire period

Weather Forecast

Friday: Heavy snow and strong southwesterly winds. 30-40cm possible by the end of the day for immediate coastal areas, but expected to be dryer inland. Freezing levels are expected to drop to 1000m. Saturday and Sunday: Continued moderate snowfall and strong south to southwest winds with freezing levels remaining in the 500-1000m range.

Avalanche Summary

We received an initial report of an avalanche fatality in the Brandywine area on Tuesday. So far we know that a single snowmobiler was buried and perished in a Size 3 avalanche. The avalanche occurred on an east aspect at approximately 1700m, the slab was estimated to be 1.5-2.0m thick and 400m wide and suspected to have stepped-down to the mid-February persistent weakness. We will provide more details as they come available. More reports of last weekend's widespread large natural avalanche cycle are coming in with observations of Size 4.5 avalanches. Some of the larger slabs propagated 2-3Km along ridgelines and stepped down to the mid-February persistent weakness, and there's no reason why similar avalanches can't happen with this next round of loading.

Snowpack Summary

Strong and variable winds in exposed treeline and alpine areas has resulted in reverse loading, sastrugi, surface crusts, and looming undermined cornices. Dribs and drabs of new snow over the past couple of days adds to the approximately 50cm of recent low density storm snow. Loose surface snow, storm slabs, and/or weak wind slabs are bonding poorly to a variety of old snow surfaces, including crusts, faceted snow, and wind slabs, from last week. Recent winds and precipitation patterns have created a highly variable somewhat upside-down upper snowpack. Storm and wind slabs have shown propensity to release mid-slope, propagate into low angled terrain, and step-down to deeper weaknesses.

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.

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.