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Avalanche Forecast

Archived

Jan 14th, 2014–Jan 15th, 2014

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
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 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.

Regions

Purcells.

Confidence

Fair - Freezing levels are uncertain on Friday

Weather Forecast

Synopsis:  The interior of BC will come under the influence of a strong ridge of high pressure and warm temperatures for the next few days.Overnight: Light precipitation, winds changing to mod to strong W,  freezing levels at valley bottom.Wednesday: Some sunny periods, winds moderate to strong from the west, freezing levels to 1400 M in parts of the forecast area.Thursday: No precipitation in the forecast, sunny periods,. light winds at ridge tops freezing level rises to 1800m.Friday:  No Precipitation , sunny periods, winds light to moderate from the W-NW at ridge tops, freezing levels may rise to 2300m in some parts of the forecast area.

Avalanche Summary

There have been a number close calls with large avalanches in the north of this region in the last three weeks. Check out the incident database for more details. Reports indicate that the storm snow has not yet bonded to the older layers and wind and storm slabs are easily triggered and may propagate quite far. There is a very real possibility that a small avalanche could "step down" to the weak facetted layer at the base of the snowpack and produce a large destructive avalanche.

Snowpack Summary

Amounts of new snow are highly variable over the length of the forecast area, with the western parts of the range getting as much as 40 cm in the past 24 hrs, The eastern and southern parts have received 10 to 20. The new snow sits on a variety of snow surfaces including older wind slabs and a soft layer of facetted snow and/or surface hoar from earlier in January. All of this is sitting on top of older wind slabs and a couple of persistent weak layers in the upper meter of the relatively thin snowpack. A mid December surface hoar is buried around 30-90 cm. The early December facet/crust combo is buried down 50-150 cm. Both interfaces give variable results with snowpack tests, but professional operators are treating them with caution.A big concern, especially in the northern part of the region is a layer of weak sugary depth hoar crystals at the base of the snowpack that lie above a crust from early October. Several large avalanches in the last weeks have been attributed to failures at this layer. Wide propagations on relatively gentle terrain have been noted, and an alarming tendency for seemingly disconnected slopes to propagate over a wide area and produce large avalanche.

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.

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.