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Avalanche Forecast

Archived

Dec 4th, 2017–Dec 5th, 2017

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

Regions

Northwest Coastal.

Avalanche danger is on an increasing trend. More new snow is the first factor, followed by a bout of sustained warm temperatures that will truly test the snowpack.

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

Tuesday: Flurries bringing 10-20 cm of new snow, mainly in the morning, rain below about 1000 metres. Moderate to strong southwest winds. Freezing level to 1500 metres with alpine temperatures around -1.Wednesday: A mix of sun and cloud with no new snow. Likely alpine temperature inversion. Light south winds. Freezing level climbing to 3000 metres with alpine temperatures around +5. Cooler temperatures at valley bottom.Thursday: Mainly sunny with valley cloud due to a lingering alpine temperature inversion. Light south winds. Freezing level to 3400 metres with alpine temperatures around +5. Cooler temperatures at valley bottom.

Avalanche Summary

On Sunday, dry loose avalanches were reported up to size 1. On Saturday, reports indicated several natural wind slab avalanches up to size 2 on northerly aspects in the alpine and dry loose avalanches from steeper terrain up to size 1 treeline and above. Beyond surface instabilities, the strength of the bond between our recent storm snow and deeper buried crusts remains in question (especially at the basal crust). With this in mind, use a conservative approach to route selection by traveling through low consequence terrain, especially as we head into forecast warmer weatherCheck out the Mountain Information Network for recently posted observations around the Shames area. Give info, get info.

Snowpack Summary

Average snowpack depths in the region are roughly 100-150 cm at treeline elevations. This means that our recent accumulated storm snow (100-130 cm) forms the vast majority of our existing snowpack. Strong winds (mainly southwest) over the course of the storm developed deep deposits of wind slab on leeward slopes. The recent snow seems to be settling quickly and sits above a 5-10 cm thick crust that was buried a week ago. The crust/facet interface that was buried at the end of October can now be found 90-160 cm deep. Recent snowpack test results are showing hard compression tests with sudden collapse results on this interface. The strength of these two deep weak layers will be an increasing concern as the snowpack is forced to adjust under continued loading and forecast rapid warming.

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.

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.