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Avalanche Forecast

Archived

Mar 10th, 2019–Mar 11th, 2019

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

Regions

South Coast.

Avalanche danger will increase as a storm arrives Monday and continues into Tuesday.

Confidence

Moderate - Timing of incoming weather systems is uncertain

Weather Forecast

SUNDAY NIGHT: Increasing cloud overnight, 15-30 km/h west wind, alpine temperatures drop to -2 C.MONDAY: Snow starting midday and rapidly accumulating in the afternoon, with 15-20 cm by the evening, 30-50 km/h southwest wind, treeline temperatures near -1 C, freezing level 700 m.TUESDAY: Snow continues in the morning and eases off in the afternoon, total accumulation of 30-45 cm over the course of the storm, 20-30 km/h northwest wind, treeline temperatures near 0 C, freezing level 900 m.WEDNESDAY: Mix of sun and cloud, light northwest wind, treeline temperatures near 0 C, freezing level 900 m.

Avalanche Summary

Recent avalanche activity has been limited to small slab and loose avalanches in the top 20 cm of snow (size 1). Check recent MIN reports for some examples here and here. Looking ahead, the most likely problem will be storm slabs that form with the incoming storm, however the lingering persistent weak layer in the North Shore Mountains still poses a low likelihood - high consequence problem.

Snowpack Summary

Fresh snow will start to accumulate on Monday. Strong southwest wind will likely form drifts and slabs in exposed terrain. The new snow is falling on a sun crust on steep southerly slopes, and possibly on weak surface hoar crystals on sheltered and shaded slopes.A layer of weak and sugary faceted grains sits on a melt-freeze crust about 50 to 120 cm deep. The layer is likely most prominent in the North Shore Mountains and on north aspects. This layer continues to be reactive in snowpack tests. The problem is not typical for the region and we expect this persistent weak layer to continue to linger.The lower snowpack is generally strong.

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.

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.