Avalanche Forecast

Issued: Mar 24th, 2015 9:49AM

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

swerner, Avalanche Canada

Purcells.

Storm and/or wind slabs are expected to remain reactive to human-triggering. Use a conservative approach to terrain selection and travel.

Summary

Confidence

Fair - Due to the number of field observations

Weather Forecast

The next Pacific frontal system will reach the coast tomorrow. The front will affect most of the Interior through the forecast period. Wednesday will see light convective flurries, moderate ridgetop winds from the SW and freezing levels near 1600 m. For Thursday, precipitation amounts expected are 4-10 mm. Ridgetop winds will be strong from the SW and freezing levels rising to 2300 m. Warm air will remain over the region on Friday with freezing levels rising to 2800 m. Skies will show a mix of sun and cloud and ridgetop winds will be moderate- strong from the SW.

Avalanche Summary

On Monday, several natural avalanches up to size 2 on north and west aspects were reported. Explosive control showed avalanches up to size 2 mostly from northerly aspects above 2300 m. On Wednesday, wind slabs are expected to reactive to human-triggering. Where enough new snow exists, it may be possible to trigger storm slab avalanches up to size 2.5.

Snowpack Summary

Recent snowfall amounts vary greatly across the region. The NW part of the region received up to 60 cm while the Dogtooth received around 30 cm and the far south received close to zero. At higher elevations, this dense storm snow sits over the mid-March interface which had included crusts, moist snow, wind affected surfaces, and/or old wind slabs. In exposed terrain, strong SW winds had redistributed new snow into wind slabs on leeward features. Snow surfaces are wet around 1800 m and moist to around 2200 m. The snow surface is expected to undergo melt-freeze cycles as freezing levels drop overnight. On average, 20-50 cm below the surface is the mid-February facet/crust interface. This interface has not been reactive in the Purcells but has been very reactive in the neighboring North Columbia region. Deeper persistent weak layers in the snowpack have been dormant for several weeks, however shallower snowpack areas may be suspect.

Problems

Wind Slabs

Wind slabs found in lee terrain continue to be reactive to human triggering. This is expected to be a fairly widespread problem across most of the region for wind loaded areas of the alpine.

Be cautious as you transition into wind affected terrain.>Use ridges or ribs to avoid pockets of wind loaded snow.>

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

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

1 - 4

Storm Slabs

This problem is likely specific to the NW part of the region where the recent snowfall accumulations were greater. Storm slabs are expected to be reactive to human-triggering in steep terrain.

Use conservative route selection, stick to moderate angled terrain with low consequence.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 4

Valid until: Mar 25th, 2015 2:00PM