Avalanche Forecast

Issued: Mar 20th, 2015 9:20AM

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

rbuhler, Avalanche Canada

South Rockies.

New snow with strong winds will form touchy wind slabs at upper elevations. Use conservative terrain selection and avoid wind-loaded features.Check out the new video by the South Rockies Field Team in our blog section: www.avalanche.ca/blogs

Summary

Confidence

Fair - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

A storm system will bring light precipitation to the region on Saturday. Models are currently forecasting 3-6mm. Freezing levels will start at over 2000m but should fall to around 1500m by the end of the day meaning rain may switch to snow at many elevations. Alpine winds are expected to be strong from the SW. On Sunday, a weak ridge of high pressure should build over the interior resulting in a mix of sun and cloud. Freezing levels on Sunday are forecast to reach around 2000m and alpine winds should be light. Another storm system may reach the region on Monday bringing light precipitation.

Avalanche Summary

A widespread natural avalanche cycle to size 2.5 occurred on Monday during the storm. These were primarily storm slab avalanches but several stepped down to deeper persistent weak layers or to the ground in steep unskiable terrain. At lower elevations, loose wet avalanches up to size 2.5 were reported as well as isolated wet slabs. Natural avalanches quickly tapered off during the storm but touchy conditions existed through the week. Winds increased on Thursday and wind slab formation has been ongoing since. With strong winds and precipitation continuing on Saturday, wind slabs will continue to build and are expected to be touchy. Loose wet avalanches are a problem at lower elevations where it is raining.

Snowpack Summary

A moist or wet snow surface is expected on all aspects to around treeline and on sun-exposed slopes into the alpine. Dry snow can likely still be found on sheltered high elevation slopes. Ongoing strong SW winds are redistributing the surface snow in exposed high elevation terrain. New wind slabs are expected to be building in leeward features and will be enhanced with the upcoming snowfall. A weak rain crust from last weekend is down 30-50cm and has a good bond with snow above. There are a couple older persistent weak layers in the midpack that are still intact and have the potential to wake-up with substantial warming or heavy loading. Cornices may become fragile with afternoon warming.

Problems

Wind Slabs

Strong winds and new snow are forming wind slabs which are expected to be touchy on Saturday.

Use ridges or ribs to avoid pockets of wind loaded snow.>Avoid freshly wind loaded features.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Loose Wet

Rain at lower elevations will weaken the upper snowpack and increase the likelihood of loose wet avalanches.

Avoid steep slopes during periods of rain.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Deep Persistent Slabs

A crust/facet layer down 90-150cm still has the potential to produce very large avalanches with a heavy trigger like a cornice failure or a smaller avalanche in motion stepping down.

Caution around convexities or areas with a thin or variable snowpack.>Be aware of thin areas that may propogate to deeper instabilites.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

3 - 6

Valid until: Mar 21st, 2015 2:00PM