Avalanche Forecast

Issued: Mar 27th, 2013 10:41AM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is low. Known problems include Cornices, Persistent Slabs and Loose Wet.

swerner, Avalanche Canada

Kootenay Boundary.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain on Thursday

Weather Forecast

A split-flow pattern will be keeping things fairly benign; the most significant change through the forecast period will be warmer temperatures (above seasonal norms), and higher freezing levels. Residual moisture will persist with no significant precipitation. However, more cloud cover will be seen until Friday afternoon.Thursday: Broken cloud cover. Alpine temperatures near 1.0 degree. High diurnal temperature swings up to 2000 m in the afternoon. Ridgetop winds will blow light from the West.Friday: Scattered cloud cover. Alpine temperatures near 3.0. Freezing levels 2000 m and ridgetop winds light from the West.Saturday: Clear skies. Alpine temperatures -2.0 and freezing levels 1900 m. Ridgetop winds light from the West.

Avalanche Summary

On Tuesday, numerous loose wet avalanches and slab avalanches occurred mostly from East-West aspects up to size 2.5. Some of these avalanches ran on the mid-March crust interface.Be aware of continued natural loose wet, or wet slab avalanche activity especially on solar aspects.

Snowpack Summary

Large fragile cornices loom over many slopes. These may become weak and fail due to the influence of the sunshine. Cornice fall can act as a large trigger on slopes below, and may trigger a deeper instability if it exists. Surface snow has become moist up to 2000 m, and melt-freeze crusts are forming on solar aspects. On Northerly aspects surface hoar and surface facetting is occurring.Last week's storm snow has settled into a cohesive slab overlying an old crust (down 50-60 cm) which exists up to ridge top. The crust appears to have gained some strength in most places, but test results are still showing sudden planar fracture characteristics and may be easily triggered in certain areas by riders/skiers, cornices or smaller avalanches. Deeper down, another buried surface hoar layer sits approximately 80 cm. In some places it may not be a concern due to the thick supportive crust that lies above it. However, it may be more reactive to a trigger from a variable, thin snowpack area or a large trigger.

Problems

Cornices

Solar radiation and warm daytime temperatures, cornices may become unstable. There is a chance the weight of a cornice dropping onto the slope below could trigger an avalanche on the Mid-March crust.

Extra caution needed around cornices with current conditions.>Stay well back from cornices.>

Aspects: North, North East, East, South East.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 5

Persistent Slabs

Slab avalanches have been reactive to human triggering. The weak interface being the Mid-March crust down 40-60 cm below the surface. It may be more reactive in areas that have been slightly affected by the wind.

Dig down to find and test weak layers before committing to a line.>Be aware of thin areas that may propagate to deeper instabilites.>Plan escape routes and identify safe zones before committing to your line.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Loose Wet

Solar aspects are likely to see loose wet avalanches when the sun comes out and temperatures start to warm. There is a danger that surface avalanches may step down to pull out slabs on the buried crust.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>

Aspects: North, North East, East, South East.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Valid until: Mar 28th, 2013 2:00PM