Avalanche Forecast

Issued: Mar 26th, 2015 9:26AM

The alpine rating is high, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Storm Slabs, Persistent Slabs and Loose Wet.

swerner, Avalanche Canada

South Columbia.

A complex and unpredictable snowpack exists. Avalanche Canada has released a Special Avalanche Warning for this region. Check out the details here: http://www.avalanche.ca/news/VRHTjCUAADQcpVdL/spaw-150324

Summary

Confidence

Fair - Intensity of incoming weather systems is uncertain

Weather Forecast

Unsettled warm, wet and windy conditions will continue through the weekend. As the stationary cold front slowly slides southward, cooler air will replace the warm air overnight Friday before another weaker storm sets up on Saturday. On Friday, a mix of sun and cloud with light precipitation up to 10 mm is expected. Strong SW ridgetop winds and freezing levels will stay near 2600 m. Freezing levels will then drop overnight and hover around 1700 m on Saturday. Ridgetop winds will blow moderate to strong from the SW-W and light convective precipitation will continue. On Sunday, precipitation amounts 3-12 mm are expected with ridgetop winds strong from the west. Freezing levels will stay steady around 1700 m.

Avalanche Summary

On Wednesday, several natural large cornice failures up to size 2.5 were reported along with a natural size 2 storm slab from NW-SE aspects above 2200 m. I suspect the region saw a natural avalanche cycle with Thursday's storm, however; reports across the region have yet confirmed distribution, size and magnitude. On Friday, natural avalanche activity will likely continue with warm temperatures, strong winds and periods of sun and rain. Avalanches failing on the mid-March persistent interface will be large and destructive.

Snowpack Summary

New dense snow up to 25 cm at higher elevations has added load to the previous storm snow that sits over the mid-March interface 40-60 cm down. This interface is comprised of a series of crusts, wind affected surfaces, and old wind slabs which has recently come alive and has been reactive, especially in the North (Revelstoke and surrounding area). Snow-pit testing varies regionally, with this interface generally showing moderate to hard results with a resistent-sudden planar fracture characteristic. Recent snowfall amounts taper off towards the south of the region. Strong SW winds had redistributed the new snow into wind slabs on leeward features. Digging deeper, 50-80 cm is the mid-February facet/crust interface. There is some concern for this layer to wake-up in the South Columbia region and storm slab avalanches have the potential to step down to it. From 2200 m down, the upper snowpack has become wet, and has seen no significant re-freeze overnight.

Problems

Storm Slabs

Rising temperatures, wind, snow and rain are likely increasing the reactivity of the storm slabs. Natural avalanches and human triggered avalanches are likely. These slabs may be moist or wet at lower elevations.

Use conservative route selection, stick to moderate angled terrain with low consequence.>Avoid steep, open slopes.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Persistent Slabs

A persistent weak layer is buried anywhere from 40-80 cm below the surface and has produced numerous large avalanches recently. Storm slab avalanches could easily step down to this layer and remote triggering is possible.

Be aware of the potential for wide propagations and remote triggering due to a buried weak layer.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

3 - 5

Loose Wet

Rising freezing levels, warm temperatures and periods of sunshine will likely deteriorate the upper snowpack, resulting in loose wet avalanche activity.

Watch for clues, like natural avalanche activity, sluffing off of cliffs, moist surface snow, and snowballing. These are indicators that the snowpack is warming up and deteriorating.>Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Valid until: Mar 27th, 2015 2:00PM