Avalanche Forecast

Issued: Mar 4th, 2016 7:59AM

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

triley, Avalanche Canada

Purcells.

Forecast new snow and wind are expected to continue to allow for easy triggering of storm slabs.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

Freezing levels remaining above 1500 metres overnight with moderate southwest winds. 3-5 cm of new snow and moderate southwest winds expected during the day on Saturday with freezing levels rising to 2000 metres. Another 5-10 cm of new snow on Sunday with moderate winds and freezing levels above 1500 metres. A weak ridge should drop freezing levels to valley bottoms by Monday morning, before broken or scattered cloud allows the sun to bring the freezing level back up to 1500 metres during the day.

Avalanche Summary

No new natural avalanches reported on Thursday. One skier remote size 2.0 storm slab avalanche was reported from an east aspect in the alpine. Explosives triggered avalanches up to size 2.5 on various aspects. One new natural cornice fall was reported on Friday.

Snowpack Summary

15-30 cm of recent storm snow is bonding poorly to a melt-freeze crust on previously sun-exposed slopes and lower elevation terrain, and/or a layer of surface hoar on shady and sheltered slopes at treeline elevations. Thicker and touchier fresh wind slabs are lurking in exposed lee and cross-loaded terrain. The surface hoar and/or crust layer buried in mid-February is now down 40-70cm. This layer was less reactive over the past week with cooler temperatures. Large weak cornices remain concerning and have recently triggered persistent slabs on slopes below. The early January surface hoar/facet layer is typically down 70-120cm. Triggering an avalanche on this layer has become unlikely but it still has isolated potential to produce very large avalanches with a heavy trigger. In general, the lower snowpack is well settled and strong, apart from some thin snowpack areas where basal facets exist.

Problems

Storm Slabs

Storm slabs continue to develop with new snow and wind. Storm slabs may be sitting on a weak layer of surface hoar, a crust, or a crust/surface hoar layer that allows for easy triggering.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>Be cautious as you transition into wind affected terrain.>Use ridges or ribs to avoid pockets of wind loaded snow.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

The February 10th surface hoar layer is buried down about 60 cm in most areas. High freezing levels and continued loading from new snow and wind may increase the likelihood of triggering this persistent weak layer.

Caution around convexities or areas with a thin or variable snowpack.>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

2 - 5

Cornices

Cornices are large and fragile and may continue to grow with forecast new snow and wind. Warm temperatures and high freezing levels may result in natural cornice falls.

Give cornices a wide berth when travelling on or below ridges.>Extra caution needed around cornices with current conditions.>

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

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 4

Valid until: Mar 5th, 2016 2:00PM