Avalanche Forecast

Issued: Mar 4th, 2013 8:23AM

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

pmarshall, Avalanche Canada

Sea To Sky.

Summary

Confidence

Fair

Weather Forecast

Synopsis: A weak weather system will bring more cloud and light precipitation to the South Coast for Tuesday and Wednesday. A ridge of high pressure should build in for Thursday and Friday bringing mainly sunny skies. Tuesday: Increasing cloud with light precipitation (2-4 cm). The freezing level will rise to around 1100 m during the day. Winds are light from the southeast. Wednesday: Cloudy with light precipitation (4-8 cm). The freezing level is around 1200 m and winds are light from the southeast. Thursday: A mix of sun and cloud. The freezing level is steady around 1200 m.

Avalanche Summary

A widespread natural avalanche cycle (with avalanches from size 2-4) occurred on Friday/Saturday in response to intense storm-loading. Numerous large, deep fracture lines can be seen from the Sea-to-Sky corridor. Many of these failed low in the start zone, leaving hangfire (unreleased areas of the slope). Natural avalanche activity slowed down on Sunday but explosive control continued to produce results up to size 3 and there were a couple reports of skier triggered avalanches up to size 2, primarily from north through east aspects in the alpine.

Snowpack Summary

Strong NW winds redistributed storm snow onto south and east aspects on Saturday. This reverse loading may have left wind slabs in unexpected locations.The recent storm delivered well over 100 mm of precipitation, which fell with warming temperatures, dropping rain below about 1500-1900 m, depending on location. Strong southerly winds during the storm created wind slabs on lee terrain. Numerous weaknesses developed within the storm snow. A weakness of surface hoar and/or a crust exists within the upper snowpack (now 1-2 m deep), which has been reactive over the last week, creating very large avalanches. Direct sunshine may trigger some further shedding of storm snow on Monday. The lower snowpack is well settled.

Problems

Wind Slabs

Strong winds switched direction on Sunday, meaning that wind slabs may be found on many slopes, perhaps in unusual locations.

Highmark or enter your line well below ridge crests to avoid wind loaded pillows.>Be cautious as you transition into wind affected terrain.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Storm Slabs

Well over 1 m of storm snow fell over the past several days. Weaknesses have been observed within the new snow. This new snow also sits on a persistent weak layer (down 100-200 cm) which could be triggered, resulting in a very large avalanche.

The new snow will require several days to settle and stabilize.>Avoid paths that have not avalanched recently.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 6

Cornices

Cornices have grown large and weak in recent storms. Northerly winds and daytime warming could be enough to cause cornices to fail.

Give cornices a wide berth when travelling on or below ridges.>Do not travel on slopes that are exposed to cornices overhead.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 6

Valid until: Mar 5th, 2013 2:00PM