Avalanche Forecast

Issued: Mar 17th, 2015 9:02AM

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

swerner, Avalanche Canada

Purcells.

Recently formed slabs remain sensitive to human triggering at higher elevations. Solar radiation and its destabilizing effect on the snowpack remain possible even if skies are cloudy.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain on Wednesday

Weather Forecast

The dry conditions and sunny skies are coming to an end as a series of pacific frontal systems hit the coast and bring cloudy skies and precipitation into the weekend. Wednesday will be fairly dry with a mix of sun and cloud. Ridgetop winds will be light-moderate from the West and freezing levels hover around 1500-1700 m. Thursday will bring light snow amounts 5-10 cm. Ridgetop winds will blow strong from the SW and freezing levels will rise to 1800 m. Friday will remain cloudy with light precipitation and freezing levels 2000-2500 m.

Avalanche Summary

On Monday, several natural slab avalanches up to size 2.5 were reported. Most of these initiated from northerly aspects 2000-2500 m in elevation. Numerous explosive controlled slab avalanches were also initiated up to size 2.There is a still a concern for avalanches to step down to deeply buried weak layers resulting in larger persistent slab avalanches, especially in shallower snowpack areas.

Snowpack Summary

At higher elevations, new snow sits over a plethora of surfaces including moist snow, crusts, wind affected surfaces, and/or old wind slabs which may still be reactive to rider triggers. Rain has soaked the upper snowpack to around treeline elevation forming a spring-like, melt-freeze crust. In the alpine, strong winds have redistributed the new snow into wind slabs in leeward terrain features. Prior to the storm, 10-30cm of snow was sitting over a weak facet/crust layer that was buried in mid-February. This interface has not been as reactive in the Purcell's like it has in neighboring regions; however, it does exist and should remain on your radar. The late-Jan crust/surface hoar layer can be found around 1m below the surface in deeper snowpack areas. The mid-January surface hoar can be found below that. These layers have gained significant strength and have been dormant for several weeks.

Problems

Storm Slabs

New storm slabs have formed. These slabs sit over a weakness from mid-February and are reactive to human-triggering. Thicker touchy wind slabs can be found in leeward terrain features.

Avoid freshly wind loaded features.>Use conservative route selection, stick to moderate angled terrain with low consequence, these storm slabs may take several days to stabilize.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Loose Wet

Solar radiation and daytime warming will likely deteriorate the upper snowpack, initiating loose wet avalanches. Overhead hazards like cornices could also fail and trigger slab avalanches from the slopes below.

Give cornices a wide berth when travelling on or below ridges.>Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Valid until: Mar 18th, 2015 2:00PM