Avalanche Forecast

Issued: Mar 6th, 2016 9:12AM

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

triley, Avalanche Canada

Purcells.

Storm slabs continue to be a concern. Wide fracture propagations are possible where the storm snow is sitting on a weak buried layer of surface hoar.

Summary

Confidence

Moderate - Freezing levels are uncertain

Weather Forecast

Freezing level dropping down close to valley bottoms overnight with continued light precipitation. Light precipitation and cloudy skies on Monday combined with light southerly winds and freezing levels climbing up to about 1700 metres. A spring diurnal freeze/thaw cycle setting up for Tuesday and Wednesday with freezing levels dropping to valley bottoms overnight and then rising up to 1500 metres during the day. The next major storm pulse developing on Wednesday night.

Avalanche Summary

Natural wind slabs and storm slabs up to size 2.5 were reported on Saturday. 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

Strong southerly winds have developed wind slabs in the alpine and at treeline. The 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. 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

Wind Slabs

New wind slabs have developed in the alpine and at treeline due to strong southerly winds and warm temperatures. Wind slabs may be sitting on the buried surface hoar layer from February 27th.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

Persistent weak layers of buried surface hoar may continue to be triggered by large loads like cornice falls or a large group of sledders re-grouping. Avoid un-supported terrain and shallow wind effected slopes adjacent to large alpine slopes.

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: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Cornices

New cornice growth may be large and fragile. Avoid slopes beneath cornices.

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, South.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 4

Valid until: Mar 7th, 2016 2:00PM