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Avalanche Forecast

Archived

Jan 7th, 2014–Jan 8th, 2014

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

Fair - Intensity of incoming weather systems is uncertain on Wednesday

Weather Forecast

Wednesday: Light to moderate snowfall / Moderate southwest winds / Freezing level at 700mThursday Heavy snowfall arriving late in the day / Strong to extreme southerly winds / Freezing level at 600mFriday: Light to moderate snowfall / Moderate westerly winds / Freezing level at 600m

Avalanche Summary

In recent days a few slab avalanches to size 3.5 were noted in alpine terrain in the far north of the region. They were suspected to have failed on basal facets. I would expect a new round of storm slab activity with weather forecast for the next few days.

Snowpack Summary

In general the snowpack seems shallower and more faceted in the northern part of the region, and deeper with more wind slab problems in the south. At 1300m on an east aspect in the Shames area the height of snow was about 190cm. Very light amounts of new snow now overlie a variety of old surface which include: settled storm snow, surface hoar in sheltered locations, and wind slabs at upper elevations. About 30cm below the surface you may find several laminated thin melt/freeze crusts. Moderate sudden planar shears were experienced in snowpack tests down about 40 cm in a weak facet layer that is sitting above a melt/freeze crust from Christmas. Deeper early December facetted crystals were found to be rounding and gaining strength in this area.

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.