Avalanche Forecast

Issued: Mar 26th, 2015 8:51AM

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

ghelgeson, Avalanche Canada

Purcells.

Warm temperatures rising well into the alpine, combined with periods of sun and a chance of rain, will make for touchy avalanche conditions. Minimize your exposure to avalanche terrain if the snowpack is becoming moist.

Summary

Confidence

Fair - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

A pacific frontal system will affect regions to the west and north more significantly. High freezing levels will mean that precipitation will likely fall as rain. On Friday expect isolated wet flurries in the alpine, with some sunny breaks. Alpine temps are expected to reach 4'C with SW winds gusting to 60km/hr. Overnight forecast precipitation amounts vary from a trace to 10mm with freezing levels from 2500-3000m. On Saturday expect increasing sun in the afternoon, which may destabilize the new snow at higher elevations. Alpine temps will be 2'C with W winds gusting to 55km/hr. Overnight freezing levels are expected to lower to 1400m, which will hopefully provide some recovery. Sunday will be unsettled with a mix of sun and cloud, isolated flurries and freezing levels rising to 2200m.

Avalanche Summary

No new avalanches were reported on Wednesday, but visibility was poor. On Monday a size 3 was remotely triggered from a steep unsupported roll, and a size 2 was accidentally triggered by skiers. Both occurred on N-NE aspects around 2200-2300m and were 20 to 50cm deep. A solar induced natural avalanche cycle occurred Tuesday afternoon up to size 2 on southerly aspects, and explosive controlled size 2-3 slab avalanches were initiated from steep N-NE aspects above 2300 m.

Snowpack Summary

Warm temps, sunny periods and high freezing levels will make surfaces moist, with no overnight recoveries expected. At treeline and above storm snow amounts from last weekend vary. 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. This dense storm snow sits over the mid-March interface which consists of a series of crusts, old wind slabs, facets and surface hoar. On a NE aspect at 2375m on Wednesday tests results showed that this interface was easy to trigger and likely to propagate. In exposed terrain, strong SW winds had redistributed new snow into wind slabs on leeward terrain features and slopes. Below this interface is the mid-February facet/crust interface. The mid-February layer has not been reactive in the Purcells but has been very reactive in the neighboring North Columbia region. Deeper persistent weak layers that have been dormant for several weeks are not currently a problem but still have the potential to wake-up with major warming or heavy loading. Persistent weak layers may be suspect in shallower snowpack areas.

Problems

Wind Slabs

Sustained southwesterly winds, combined with warm temps and new snow at high elevations, will continue to build wind slabs. Expect wind slabs to be reactive. Use caution on lee and wind-loaded slopes.

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, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Storm Slabs

In the NW part of the region, where recent snowfall accumulations were higher, storm slabs may become increasingly reactive to human triggering as temperatures rise. Be especially cautious where the storm slab overlies a crust.

Avoid convexities or areas with a thin or variable snowpack.>Use conservative route selection, stick to moderate angled terrain with low consequence.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 5

Loose Wet

High freezing levels, warm temps without an overnight freeze, and the possibility of both rain and sun will continue to deteriorate the snowpack.

Watch for clues, like natural avalanche activity, sluffing off of cliffs, moist/ wet snow surfaces, and snowballing. These are indicators that the snowpack is warming up and deteriorating.>Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Likely

Expected Size

1 - 2

Valid until: Mar 27th, 2015 2:00PM