Avalanche Forecast

Issued: Feb 10th, 2013 8:26AM

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

swerner, Avalanche Canada

Purcells.

Summary

Confidence

Fair - Timing of incoming weather is uncertain on Tuesday

Weather Forecast

Monday: The pattern and flow starts changing today as the ridge move southward and a zonal flow sets up. An embedded cold front will move through the region bringing moderate West winds and a trace of snow. Treeline temperatures will sit near -4 and freezing levels will be around 1200 m. Tuesday: The fast paced zonal flow will continue with a trough moving in from the West bringing moderate-strong SW winds and light-moderate snow accumulations. Treeline temperatures will be near -6 and freezing levels around 1200 m.Wednesday: Another ridge is building bringing dryer conditions, especially for the short term. Ridgetop winds will be light from the West. Treeline temperatures -10 and freezing levels falling to valley bottom. Â

Avalanche Summary

No new natural avalanche activity has been reported. Evidence of a natural size 2 cycle within the last 72 hrs.

Snowpack Summary

Wind slabs

exist in the alpine and at treeline on lee slopes and behind ridgelines. The recent storm slab continues to settle over old interfaces comprising of surface hoar, crusts and facets down 30-50 cm. However, areas that have buried surface hoar seem to be most touchy. Continued freezing temperatures overnight have helped to strengthen the snowpack at lower elevations.The mid-pack is generally well settled and the average snowpack depth at treeline elevations is near 130. Cornices have grown and may threaten slopes below.

Problems

Wind Slabs

Wind slabs may be reactive to light additional loads like skiers and sledders. Areas of concern are in the immediate lees of slopes and behind terrain features like ridgelines and ribs. Cornices have grown and may threaten slopes below.

Use ridges or ribs to avoid pockets of wind loaded snow.>Highmark or enter your line well below ridge crests to avoid wind loaded pillows.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 4

Persistent Slabs

The recent storm snow continues to settle into a cohesive slab above weak layers and variable old surfaces that comprise of buried wind slabs, surface hoar, and crusts. These weak layers exist 30-50 cm below the surface. They can be tricky to manage.

Use extra caution on open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>Whumpfing is direct evidence of a buried instability.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 5

Valid until: Feb 11th, 2013 2:00PM