Avalanche Forecast

Archived

Mar 1st, 2013–Mar 2nd, 2013

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Natural avalanches possible, human triggered probable.

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.

Regions

Kootenay Boundary.

Confidence

Fair - Intensity of incoming weather is uncertain on Saturday

Weather Forecast

Saturday: A ridge of high pressure over the Kootenay region eases precipitation to light amounts during the day and moderate amounts developing in the evening. Strong winds easing to moderate from the SW. High diurnal temperature trends and freezing levels rising to 2200 m. Sunday: Light-moderate precipitation accompanied by moderate-strong ridgetop winds from the NW. Alpine temperatures near -7 and freezing levels falling to 900 m. Monday: No significant precipitation expected with ridgetop winds blowing light form the South. Alpine temperatures near -8, and freezing levels hovering around 1200 m in the afternoon.

Avalanche Summary

On Thursday natural slab avalanche activity occurred on SE aspects around 1800 m up to size 1.5. Throughout the region loose dry sluffing occurred from steeper terrain features on all aspects and elevations. I expect the avalanche activity has ramped up and will persist through the weekend with additional precipitation, rising freezing levels and strong ridgetop winds.

Snowpack Summary

In much of the region, up to 80 cm recent snow overlies weak interfaces buried in mid-February (mainly surface hoar/ sun crust layers). The storm slab above these interfaces has the potential for wide propagations and surprisingly large avalanches, especially where winds have shifted the snow into slabs in the lee of terrain breaks. A thin freezing rain/rime crust formed last Friday, which is now buried by about 20-40cm snow.In the Rossland Range, surface hoar which was buried mid-week is 20-35 cm down and exhibits easy, sudden results in snowpack tests. As more snow builds over this layer, it could become touchy.Older snowpack weaknesses buried in the upper snowpack (Feb 4th and Jan 23 surface hoar/facet/sun crust layers) are still being tracked by professionals. There is some potential for triggering one of these deeper layers with a large trigger like an avalanche in motion, or from a thin-spot trigger point. The lower snowpack is generally well settled.

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.

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.