Avalanche Forecast

Issued: Mar 27th, 2015 9:17AM

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

swerner, Avalanche Canada

Purcells.

Strong winds, elevated freezing levels combined with periods of sun and a chance of snow/ and rain, will make for touchy avalanche conditions.

Summary

Confidence

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

Weather Forecast

An unsettled, winter-like weather pattern will continue through the forecast period. A weaker storm will make way to the Interior tonight and freezing levels will drop significantly in the wake of the cold front. As the front sweeps through, light-moderate precipitation will fall and ridgetop winds will be moderate from the west. On Saturday and Sunday, accumulated precipitation 5-20 mm with ridgetop winds blowing strong from the west and freezing levels steady around 2100 m. The general weather pattern is expected to bring multiple systems but the confidence in the exact timing, track, and strength of each system is poor.

Avalanche Summary

On Thursday, wind and warming conditions were responsible for several natural slab avalanches up to size 3 from east and north aspects above 2100 m. There was also a report of a close call, skier triggered size 2.5 slab avalanche from the Dogtooth range. Extensive snowballing, and small loose wet avalanches were also reported from slopes below 2200 m. If some areas of the region see convective snow/ rain (20 mm) overnight Friday, and strong westerly winds, natural avalanche activity will likely continue on Saturday.

Snowpack Summary

Recent warm temps, sunny periods and high freezing levels will make surfaces moist; with some crust recovery/ development above 2000 m. Below that elevation no significant overnight recoveries are 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. Snow-pit tests have shown this interface to be fairly easy to trigger and likely to propagate. In exposed terrain, strong SW winds had redistributed snow into touchy wind slabs on leeward terrain features and slopes. Below this interface is the mid-February facet/crust interface. The mid-February layer has been dormant for some time, however; in neighboring regions it has been reactive. 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, especially in areas that may have buried, deep weak layers. Wide propagations are possible.

Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.>Use conservative route selection, stick to moderate angled terrain with low consequence.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

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.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>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.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Likely

Expected Size

1 - 3

Valid until: Mar 28th, 2015 2:00PM