Avalanche Forecast

Issued: Mar 5th, 2016 8:20AM

The alpine rating is considerable, the treeline rating is considerable, 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 - Forecast snowfall amounts are uncertain

Weather Forecast

Cloud developing Saturday evening, and then strong southerly winds with 3-5 cm of new snow overnight. The freezing level should remain close to 2000 metres in the south of the region overnight and on Sunday. In the north of the region, the freezing level should drop down to at least 1000 metres. Another 5-10 cm of new snow during the day Sunday combined with strong southwest winds. Freezing levels dropping to 1000 metres by Monday morning. Mostly sunny on Monday with strong solar radiation and freezing levels around 1500 metres. Cloudy with light precipitation on Tuesday.

Avalanche Summary

Natural and explosives controlled avalanches up to size 2.5 were reported on Friday. One size 3.0 avalanche released sympathetically to a cornice falling 100 metres away. 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.

Snowpack Summary

20-40 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 50-80cm. 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.

Use ridges or ribs to avoid pockets of wind loaded snow.>Be cautious as you transition into wind affected terrain.>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

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.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>Caution around convexities or areas with a thin or variable snowpack.>

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.

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

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

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 4

Valid until: Mar 6th, 2016 2:00PM