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Avalanche Forecast

Archived

Feb 1st, 2016–Feb 2nd, 2016

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

Regions

Cariboos.

Touchy persistent weak layers are making for tricky conditions. Conservative terrain selection is critical.In the North Rockies, conditions are also tricky. Check out the new blog at http://goo.gl/j4awOS or click here

Confidence

Moderate - Due to the number of field observations

Weather Forecast

On Tuesday and Wednesday morning expect a mix of sun and cloud and light northwest winds. By Wednesday evening a Pacific system will make its way inland bringing 5-10cm of new snow and strong southwest winds. Freezing levels will stay at valley bottom for the forecast period.

Avalanche Summary

On Saturday, two natural size 2.5 storm slab avalanches were reported on south-southeast aspects. A snowmobile triggered a size 1.5 persistent slab on a northeast aspect at 1900m which released on a layer of surface hoar. Several remotely triggered size 2-2.5 wind slab avalanches were reported to have been triggered from up to 100m away in the alpine and at treeline. On Sunday, a helicopter is believed to have remotely triggered a size 2.5 persistent slab avalanche at the 1900m elevation from a distance of 200m. The slab was about 400m wide, 90cm deep and is thought to have failed on the early January surface hoar. Although this avalanche occurred on the east side of Highway 5 (technically the Northern Monashees), similar touchy conditions likely exist in some parts of the Cariboos. Recently formed storm slabs and a reactive persistent slab are both expected to remain sensitive to human-triggering on Tuesday.

Snowpack Summary

Recent snowfall and strong winds created storm slabs in many places and wind slabs on features lee to the southerly winds. This new snow has also added load and stress to the already volatile persistent slab. The recently destructive layers of surface hoar from early January are now typically down 70-120cm and remain reactive. These layers have the potential for wide propagations and remote triggering, and smaller avalanches have the potential to easily step-down to one of these layers. The mid and lower snowpack are generally strong and well settled below these layers. Snowpack depths are variable across the region and shallow snowpack areas may have weak facetted crystals near the ground.

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.