Avalanche Forecast

Issued: Mar 26th, 2013 10:20AM

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

ccampbell, Avalanche Canada

South Columbia.

Summary

Confidence

Good

Weather Forecast

The ridge of High pressure is expected to continue to influence the interior ranges for the next few days. As the ridge weakens we may see high cloud reducing the exposure to strong solar radiation. Nights are expected to continue to be clear and cool. Freezing levels in the North should rise during the day to about 1800 metres, and to about 2000 metres in the South.

Avalanche Summary

Natural cornice failures and wet-loose avalanche up to Size 2.5 continue to be reported from throughout the region. This avalanche activity is expected to continue with warm and sunny weather throughout the forecast period. On Sunday, a skier accidentally triggered a Size 2.0 persistent slab avalanche on a west through southwest facing alpine slope in Glacier National Park, that resulted in one fatality. The avalanche failed on surface hoar sitting on a crust that was buried on March 11th.

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. 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 because of the potential for very large avalanches particularly with heavy triggers such as cornice falls.

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.

Cornices become weak with daytime heating, so travel early on exposed slopes.>Give cornices a wide berth when travelling on or below ridges.>Extra caution needed around cornices with current conditions.>

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Likely - Very Likely

Expected Size

2 - 6

Storm Slabs

Pockets of wind slab from localized wind, including down-flowing katabatic wind, could be rider triggered. Periods of strong solar radiation may cause loose moist or wet snow to fall out of very steep terrain.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 4

Persistent Slabs

The March 10th weak layer of surface hoar is buried down more than a metre in most places. Large loads like cornice falls may trigger this deeply buried weak layer.

Be aware of thin areas that may propagate to deeper instabilites.>Carefully evaluate and use caution around thin snowpack areas.>If your sled is bogging down, don’t spin the track and trigger the weak layer below.>Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Valid until: Mar 27th, 2013 2:00PM