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Avalanche Forecast

Archived

Dec 15th, 2013–Dec 16th, 2013

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

Regions

Northwest Coastal.

Continuing precipitation and strong SW winds will keep the avalanche danger high until the snowpack has time to adjust to the new load.

Confidence

Fair - Due to the number of field observations

Weather Forecast

Tonight and Monday: Westerly onshore flow will continue with strong westerly winds and light precipitation. Freezing levels hovering around 600m.Tuesday: Another large storm hits the Northwest with heavy precipitation and strong southwest winds. Freezing levels may spike again as the storm passes through.Wednesday: Pacific frontal system exits the area and moves off to the east. Freezing levels drop to valley bottom for most of the forecast area through the next few days as arctic air moves south.

Avalanche Summary

Numerous size 2-3 avalanches have been observed in the bear pass area. These mainly occurred on north through east slopes that are lee to strong southwest winds.The warm new snow is likely not bonding well to the weak layers formed in early december. Heightened avalanche activity and conditions will continue through Monday. Lower elevations are experiencing moist or wet natural avalanches releasing at or near the ground. This will become less of a problem once the freezing levels start descending back down to valley bottoms.  Lee slopes will be touchy at upper elevations until this storm snow gets a chance to bond.

Snowpack Summary

A mixture of heavy rain/snow/wet snow has fallen to 1500m elevation. Strong Southwest winds are transporting snow and developing deep pockets that are sitting above recent weak surface layers. Rising temperatures during the storm have likely developed a relatively warm storm slab above a cold layer of wind crusts, surface hoar and surface facets, an upside down scenario. This layer was buried anywhere from 30-50cm prior to the major Dec 14 storm.Earlier in the week, reports from the Shames area at 950m elevation suggested the mid and lower snowpack was composed of various faceted layers and a stiff 4 cm crust. Another crust can be found closer to the base of the snowpack. The recent precipitation will strengthen the snowpack at lower elevations, but may prove to be problematic with rapid wind loading at upper levels.

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.