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Avalanche Forecast

Archived

Nov 22nd, 2011–Nov 23rd, 2011

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

Regions

Sea To Sky.

This bulletin is based on limited data. Local variation in conditions and danger levels are likely to exist. To produce more accurate forecasts, we need information. Please send an email to [email protected].

Confidence

Poor - Track of incoming weather is uncertain on Wednesday

Weather Forecast

Wednesday: The track of the next intense Pacific frontal system is uncertain, but at this point it appears as though it may just miss the Sea-to-Sky region. If this is the case, then expect relatively calm and cold conditions with flurries bringing light amounts of snow accumulation. If the system does hit the Sea-to-Sky region, then periods of very heavy precipitation, strong southwesterly winds, and freezing levels fluctuating between 800m and 1500m, are expected.Thursday: Another intense system is expected to bring 30-40cm with associates strong southwesterly winds and freezing levels around 800m.Friday: A high pressure ridge is expected to dry things out.

Avalanche Summary

Large destructive natural avalanches, triggered by heavy loading from snow and wind, were observed this morning. I expect this natural avalanche activity will continue with additional loading from new snow and wind, and the likelihood of human triggering to remain for the forecast period.

Snowpack Summary

Newly formed surface hoar is now buried by 50-70cm of recent storm snow. Various persistent weaknesses including facets and surface hoar, with an associated crust at upper treeline elevations, can be found down 70-150cm. A deeper crust with associated facets and/or depth hoar is approximately 50cm off the ground.

Problems

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.

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.

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.