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Avalanche Forecast

Archived

Dec 13th, 2017–Dec 14th, 2017

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

Regions

Northwest Coastal.

Upgrade the danger rating to CONSIDERABLE if you receive more than 20 mm of precipitation in your local riding area Thursday morning.

Confidence

Moderate - Track of incoming weather systems is uncertain on Thursday

Weather Forecast

Thursday: Cloudy with light precipitation starting late in the am. Alpine temperatures high plus 4 degrees and freezing levels 1400 m. Ridgetop wind light gusting strong from the southwest.Friday: Mainly cloudy. Up to 5 cm of new snow. Alpine temperatures -2 and freeing levels 1000 m. Ridgetop wind moderate from the southwest.Saturday: Heavy snow, 20-40 cm. Alpine temperatures -2 and freezing levels 1000 m. Cloudy with sunny periods. Ridgetop wind mostly light, with strong gusts from the southwest.Check out the Mountain Weather Forecast for more detail.

Avalanche Summary

No new avalanche observations reported on Wednesday. Avalanche activity will likely increase through the forecast period with new rain, snow and wind.I'd also remain suspect of the deep persistent layers on your radar as the region receives this new load. On December 7th and 8th a few deep persistent slabs to size 3 out of steep south facing alpine terrain in the Skeena corridor west of Terrace were reported. Basal facets were thought to be the culprit in these events. The deep persistent slab is something to keep on your radar, especially with more weather in the forecast.

Snowpack Summary

Recently, the region has received up to 20 mm of rain and some new snow at high alpine elevations. The alpine and treeline has seen significant wind effect on all aspects including wind slab and wind pressed snow. Snow surfaces are highly variable and consist of rain crusts, moist snow and new dry storm snow at elevations above 1700 m. Below the surface sits a well-settled snowpack overlying several layers of interest. Down 70-100 cm you'll likely find a 5-10 cm thick crust which was buried on November 23 and in some areas, a feathery surface hoar layer down 50-60 cm producing moderate snowpack test results. The widespread crust/facet interface that was buried at the end of October can now be found 100-200 cm deep and exists region wide.

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.