Avalanche Forecast

Issued: Mar 27th, 2013 10:55AM

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

South Columbia.

Be aware of changing conditions with daytime warming and sunny skies. Watch solar slopes and overhead hazards.

Summary

Confidence

Good

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), higher freezing levels and intense solar radiation. The region will likely see more cloud cover come Friday.Thursday: Few clouds. 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 2100 m and ridgetop winds light from the West.Saturday: Few-scattered cloud clover. Alpine temperatures -3.0 and freezing levels 1500 m. Ridgetop winds light from the NW.

Avalanche Summary

Natural cornice failures and wet-loose avalanche up to Size 2.5 continue to be reported from throughout the region. One size 4.5 slab avalanche was reported from the North Columbia region. This was a cornice fall triggering multiple persistent weak layers deeper in the snowpack. This avalanche activity is expected to continue with warm and sunny weather throughout the forecast period.

Snowpack Summary

Surface faceting and surface hoar growth has been prevalent on shady slopes and at upper elevations, while the surface snow on sun-exposed slopes and at lower elevations has been subject to daily melt-freeze cycles. Cornices are reported to be very large and weakly bonded. Cornice fall has been responsible for triggering some persistent weak layers below and initiating some very large avalanches.Wind slabs are reported to be strengthening, but may continue to be sensitive to human-triggers. The weak layer of buried surface hoar from March 10th is down more than a metre in most places, and is giving variable results in snow profile tests. However, this deep persistent weakness remains a concern.

Problems

Cornices

Natural cornice falls are a concern during daytime warming. Cornices may also be triggered easily by traveling near them. Slopes with corniced entrances, or exposed to cornice falls should be avoided with these conditions.

Give cornices a wide berth when travelling on or below ridges.>Cornice fall could trigger a large, deep slab on the slope below.>Avoid alpine terrain.>

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Likely - Very Likely

Expected Size

2 - 6

Persistent Slabs

The March 10th weak layer of surface hoar is buried down more than a metre in most places. Pockets of wind slab from localized wind, including down-flowing katabatic wind, could be rider triggered.

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: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Loose Wet

Periods of strong solar radiation may cause loose moist or wet snow avalanches. Keep an eye on changing conditions: Snowballing, moist and wet surface snow are all initial indicators of deterioration.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>Be alert to conditions that change with elevation.>

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

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

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