Avalanche Forecast

Issued: Mar 16th, 2015 9:03AM

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

swerner, Avalanche Canada

Purcells.

Strong solar radiation on Tuesday will likely trigger newly formed storm slabs and loose wet avalanches, especially in the southern parts of the region. Be conservative in terrain selection and watch for changing conditions throughout the day.

Summary

Confidence

Fair - Due to the number of field observations

Weather Forecast

Tuesday will bring a mix of sun and cloud during the day. A weak front will move onto the coast bringing generally light precipitation to Interior regions later Tuesday night. Ridgetop winds light-moderate from the E-SE. Freezing levels will range from 1500-1800 m. Wednesday will see mainly cloudy conditions with light convective precipitation and will continue through midday. Ridgetop winds will blow light from the NW and freezing levels near 1600 m. By Thursday a strong front will approach the Coast and move inland bringing precipitation amounts to Interior regions anywhere from 2-10 mm. Ridgetop winds will be strong from the SW and freezing levels will hover around 1500-2000 m.

Avalanche Summary

Natural loose wet avalanche activity has been reported on N-NW aspects from 2100-2700 m. Explosive controlled slab avalanches up to size 3 were also reported from northerly aspects above 2400 m. During the last few days there have been some concerning avalanches in the neighboring Columbia regions including natural slabs releasing to ground and very reactive wind slabs over facets being remotely triggered. On Tuesday, touchy slab avalanches are expected in the alpine and loose wet sluffing is possible from steep slopes at all elevations due to the effects of solar radiation. 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. In the alpine, strong winds during the storm are redistributing 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. 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 but have the potential to wake-up with the current warm temperatures and loading.

Problems

Storm Slabs

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

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

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.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Valid until: Mar 17th, 2015 2:00PM