Avalanche Forecast

Issued: Mar 29th, 2017 4:35PM

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

swerner, Avalanche Canada

Purcells.

The sun packs a punch this time of year. If it shines you can expect the recent storm snow to become weak and reactive. Overhead hazards like cornices may fail and trigger large slab avalanches from the slope below.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

A weak upper trough behind the current low will continue to bring unsettled conditions to the Interior. Periods of sunshine expected for Thursday and Friday.Thursday: A mix of sun and cloud. Alpine temperatures near -4 and freezing levels 1800 m. Ridgetop winds L-NW. Friday: A mix of sun and cloud. Alpine temperatures near -3 and freezing levels 1900 m. Ridgetop winds L-SW.Saturday: Trace of new snow. Alpine tmepertaures near -3 and freezing levels 1800 m. Ridgetop winds M-SW.

Avalanche Summary

On Tuesday, a couple of skier controlled slab avalanches were reported up to size 1.5 running on a buried crust on southerly aspects 10-15 cm deep and around 2400 m. With warming, solar radiation and wind, natural avalanche activity may continue and rider triggering is likely. Fragile cornices are also suspect, they are large enough and act as heavy triggers for deeper slab avalanches to release on the slopes below. If you're traveling below treeline where the avalanche hazard is lower than it is in the alpine you should remain diligent with your terrain use, mitigate overhead hazards by avoiding or lingering in run-out zones where large avalanches could come down from above. Check out the recent Forecaster Blogs for more details.

Snowpack Summary

Up to 10 cm of recent snow has fallen at upper elevations and caps a sun crust on solar aspects. This brings 20-40 cm of accumulated snow over the past week. This recent snow overlies a widespread crust below 2300 m and higher on solar aspects. Alpine wind has recently been strong mainly from the SW and has loaded leeward slopes in exposed terrain at treeline and in the alpine. Large, fragile cornices also exist along ridgelines. At lower elevations, there may be multiple crust layers in the upper snowpack which are now generally well bonded. At higher elevations, the February crust/facet layer is now down around 90-150 cm and has been reactive with several avalanches recently releasing on it. It is expected to be most reactive in the alpine where the snowpack remains dry. The deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack and a few avalanches and cornice falls have stepped down to these layers recently resulting in very large avalanches.

Problems

Wind Slabs

Recent wind from the SW has redistributed the new storm snow in exposed terrain at higher elevations forming reactive wind slabs. Cornices are large and may become weak with daytime warming, sun exposure, or during stormy periods.

Use ridges or ribs to avoid pockets of wind loaded snow.Minimize exposure to overhead hazards and sun exposed slopes when the solar radiation is strong.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Persistent Slabs

A cornice fall or smaller slab avalanches could trigger deep, destructive avalanches on buried weak layers. There is a low likelihood of triggering but a high consequence if triggered. These avalanches would likely run full path.

Use conservative route selection, choose moderate angled and supported terrain with low consequence.If triggered, wind slabs or cornices may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Loose Wet

Warmer temperatures and rain may deteriorate the lower elevation snowpack, initiating loose wet avalanches that may slide easily on a buried crust. If the sun shines this problem could extend high into the alpine on solar aspects.

Be alert to conditions that change with elevation.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 - 2

Valid until: Mar 30th, 2017 2:00PM