Avalanche Forecast

Issued: Feb 26th, 2013 9:48AM

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

ccampbell, Avalanche Canada

Northwest Coastal.

Summary

Confidence

Fair - Intensity of incoming weather is uncertain for the entire period

Weather Forecast

Wednesday: Snow with 10-15cm of accumulation throughout the day, freezing levels rising throughout the day to near 800m for coastal areas, and moderate southwesterly winds increasing to strong southerlies by the afternoon. Thursday: Continued snowfall overnight with an additional 10-15cm by Thursday morning with an additional 15-20cm throughout the day accompanied by strong southerly winds. Freezing levels rising as high as 1000m by the evening. Friday: A warm and very wet system is expected to blow over Thursday night with an additional 20-25cm by Friday morning when it is currently expected to dry out throughout the day. Freezing levels are expected to peak at 1000m and gradually lower as things dry out. Strong to extreme southerly winds associated with the height of the storm should also diminish and shift to southwesterlies as things dry out throughout the day on Friday.

Avalanche Summary

Recent reports include observations numerous natural loose-snow avalanches up to Size 2 on all aspects at all elevations from the weekend. These avalanches were generally dry in alpine areas and on shaded slopes, and moist below treeline and on sun-exposed slopes at treeline. Several natural slab avalanches up to Size 2 were also observed on southeast through west aspects in the alpine. On Monday 20cm deep Size 1.5 soft wind slab avalanche was skier-controlled on a northwest facing alpine feature, but extensive slope cutting on large steep alpine slopes and a couple of very large controlled cornice drops didn't trigger any avalanches. A very large natural ice fall avalanche also occurred on a glacier in Bear Pass.

Snowpack Summary

New snow is adding to the recent settled storm snow overlying a crust, old wind slab, and/or surface hoar depending on location, aspect and elevation. Last week a snowpack test in the Shames Valley resulted in a sudden planar shear on the buried surface hoar, down around 60 cm at the time. Most areas are reporting that the snow has bonded well to the underlying crust. The mid and lower snowpack is generally well settled and strong. The exception seems to be shallow snowpack areas where basal facets are are a concern.

Problems

Wind Slabs

Significant easterly outflow winds on Tuesday likely resulted in widespread reverse loading with lots of snow available for transport.

Avoid travelling in areas that have been reverse loaded by winds.>Be cautious as you transition into wind affected terrain.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Storm Slabs

New and recent storm snow is expected to become very touchy with continuous loading throughout the forecast period. Thinner slabs failing within the recent storm snow may step down to old snow surfaces from last week.

Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>Choose well supported terrain without convexities.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 5

Cornices

Large weak cornices have formed on the north through east side of ridge crests, while smaller cornices from recent northwesterly winds are still evident on southern aspects.

Stay well to the windward side of corniced ridges.>Avoid steep slopes below cornices.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

2 - 5

Valid until: Feb 27th, 2013 2:00PM