Avalanche Forecast

Issued: Mar 3rd, 2013 9:47AM

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.

swerner, Avalanche Canada

Purcells.

Summary

Confidence

Fair - Due to variable snowpack conditions on Monday

Weather Forecast

The pattern turns cooler, with mainly cloudy skies. The next low pressure system will begin to effect the region on Tuesday, bringing cloud cover and new snow.Monday: The ridge will move over all regions and dominate the weather pattern. Lingering cloud until mid-day with possible sunny skies in the afternoon. Ridgetop winds light from the South. Alpine temperatures near -7 and freezing levels around 1100 m in the afternoon. Tuesday: The low will bring a milder southerly flow over the region and push a weak and poorly timed upper wave across the Kootenay, Columbias and South Rockies. Alpine temperatures -6 and freezing levels 1400 m. Ridgetop winds light from the SW. Wednesday: Light-moderate snow amounts with ridgetop winds light from the South. Alpine temperatures near -7 and freezing levels 1400 m falling to valley bottom overnight.

Avalanche Summary

On Saturday the region saw a widespread natural avalanche cycle up to size 3. Most of these avalanches failed within the new storm snow from all aspects, however the N-E aspects were the most active. Avalanche activity occurred at 1500 m and above. There were a couple reports of the failing layer being the February 12 surface hoar. The size of those avalanches were 2.5, around 2400 m and on N-E aspects. Natural activity may spike if the sun shines through on Monday. Skier, and rider triggers are likely.

Snowpack Summary

Moderate amounts of new snow fell over the past couple days, adding to an ongoing storm snow instability, particularly on the west side of the region where accumulations have been highest. The variably reactive February 12th and 15th surface hoar layers now exist up to 80cm below the surface and seem most prevalent on the west side of the region. This interface may also be reactive on solar aspects where a sun crust exists.A surface hoar layer buried on February 23 is still on the radar of some operators. This layer has been less likely to trigger by skiers, but may still be sensitive to large loads like avalanches in motion or cornice fall.The mid and lower snowpack are generally well settled and strong.

Problems

Storm Slabs

Recent new snow and wind have created new slabs. These may be particularly touchy on slopes in the lee of the wind. It may take several days for the storm snow to settle out. Skier and rider triggering is likely. Watch sluffing from steeper terrain.

Avoid lee and cross-loaded terrain near ridge crests.>Avoid paths that have not avalanched recently.>Choose conservative lines and watch for clues of instability.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 5

Persistent Slabs

Loading from new snow and wind may add reactivity to persistent buried surface hoar layers. In deeper snowfall areas, resulting avalanches may be large and destructive.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 6

Cornices

Large looming cornices exist on ridgelines. These cornices may be weak and fail. The weight of cornice fall could trigger a slab avalanche on the slope below.

Give cornices a wide berth when travelling on or below ridges.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 5

Valid until: Mar 4th, 2013 2:00PM