Avalanche Forecast

Issued: Mar 27th, 2017 4:34PM

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

swerner, Avalanche Canada

Cariboos.

Convective spring-like weather may bring localized higher snowfall amounts. Moderate winds continue to build reactive wind slabs at higher elevations on the leeward side of terrain features.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

Tuesday: Unsettled conditions and convective air could bring 10-20 cm of new snow with mostly cloudy skies. Ridgetop winds will be moderate-strong from the SW and freezing levels near 1500 m. Wednesday: Snow amounts 10-20 cm. Ridgetop winds light-moderate from the South and freezing levels near 1600 m.Thursday: Cloudy with possible sunny breaks. Ridgetop winds light from the SW and freezing levels near 1500m.

Avalanche Summary

On Sunday, natural storm slab avalanches were observed up to size 2 and cornice failures triggering slabs from the slopes below up to size 2.5 were also reported. The recent storm snow is expected to be reactive at higher elevations, especially in wind loaded terrain and on steep convex features. Cornices are large and may become weak with daytime warming or during stormy periods. We are in a low probability, high consequence scenario for persistent slab avalanches failing on deep buried weak layers. Click here for more details. Click here for the new Forecasters Blog.

Snowpack Summary

20-40 cm of snow has now accumulated over the past week which overlies a rain crust at lower elevations or a sun crust on solar aspects at higher elevations. Alpine wind has recently been strong mainly from south through west directions and has loaded leeward slopes in exposed terrain at treeline and in the alpine. Large, fragile cornices are also reported in the alpine. At lower elevations, there may be multiple crust layers in the upper snowpack which are now expected to generally be well bonded and stable. At higher elevations, the February crust/facet layer is down 100-150 cm and woke up during last week's storm with many avalanches stepping down. The deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack and a few avalanches and cornice falls also stepped down to these layers recently resulting in some very large full depth avalanches. Heavy triggers like cornices and explosives continue to sporadically trigger deep weaknesses in the snowpack as recently as Saturday.

Problems

Wind Slabs

Recent wind from south through west directions has redistributed the new storm snow in exposed terrain at higher elevations forming reactive wind slabs.

Use caution on steep open slopes and convex rollsUse 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 - 2

Persistent Slabs

Sustained sun exposure, heavy triggers like a cornice falling or even under the weight of a person hitting the sweet spot could trigger deep, destructive avalanches on buried weak layers.

Pay attention to overhead hazards like cornices which could easily trigger persistent slabs.Use conservative route selection, choose moderate angled and supported terrain with low consequence.If triggered, wind slabs or cornices may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Cornices

Cornices are large and may become weak with daytime warming, sun exposure, or during stormy periods.

Pay attention to overhead hazards like cornices.Give cornices a wide berth when travelling on or below ridges.Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 3

Valid until: Mar 28th, 2017 2:00PM