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Avalanche Forecast

Archived

Apr 19th, 2014–Apr 20th, 2014

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

Regions

Kootenay Boundary.

Check out this Forecasters Blog post for more info on how to manage risk during the spring. Here's a quote: "resist the urge to rely on danger ratings alone". Conditions change rapidly at this time of year and you need to stay tuned in locally.

Confidence

Poor - Due to the number of field observations

Weather Forecast

Sunday: Mix of sun and cloud / Light to moderate southwest winds / Freezing level at 1700 mMonday: Overcast skies / Moderate south winds / Freezing level at 2600 mTuesday: Moderate snowfall / Moderate southwest winds / Freezing level dropping throughout the day to about 1900 m

Avalanche Summary

Recent observations have been limited, although on Friday we received reports of several size 1 wind slabs within the recent storm snow with at least 1 stepping down to a recently buried melt-freeze crust.Last Sunday there was a report of a size 2.5 natural deep persistent slab in the Rossland Range in response to strong solar radiation and warm temperatures. This avalanche released on a steep southeast aspect at around 2100 m and likely failed on the mid February weak layer. It's a good reminder of the potential for large deep avalanches under certain conditions.

Snowpack Summary

Some areas may have received between 40 and 50 cm of snow in the last 3 days, with a snow line somewhere around 1500-1600 m. Below the recent snow you'll likely find a melt-freeze crust in many areas. Moderate to strong westerly winds have shifted the recent accumulations into wind slabs in higher elevation lee terrain. Reports from the field indicate a weak bond exists within the storm snow, although I expect moderate temperatures over the weekend will help to settle and strengthen the new snow. The late January/early February persistent weak layer is deeply buried but could still wake up during periods of heavy precipitation (especially rain) or significant warming and solar radiation. Cornices are large in some areas and should be given a wide berth.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

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.

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.