Avalanche Forecast

Issued: Mar 24th, 2017 3:28PM

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

rbuhler, Avalanche Canada

North Columbia.

Tricky conditions are expected to persist at higher elevations with new snow and wind building slabs as well as the continuing possibility of avalanches releasing on deep weak layers. Conservative terrain selection remains highly recommended.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain on Saturday

Weather Forecast

5-15 cm of snowfall is expected Friday overnight with moderate to strong southwest wind in the alpine and freezing levels around 1000 m. Another 3-6 cm is expected on Saturday with the possibility of sunny breaks in the afternoon. Alpine wind is forecast to be moderate from the southwest and freezing levels are expected to reach around 1500 m. On Sunday, a mix of sun and cloud is expected with light alpine wind and freezing levels reaching around 1700 m. Mainly cloudy conditions are forecast for Monday with light snow flurries.

Avalanche Summary

On Thursday, a natural cornice release occurred on a north aspect at 2100 m. A few natural wind slabs were reported as well as a few solar triggered loose avalanches. Skiers were triggering wind slabs and storm slabs up to size 1.5, mainly on northwest through east aspects in the alpine. Most of these slabs were 10-30 cm thick but one was 50-60 cm thick and release on the mid-March crust. Explosives triggered a few cornices and slabs 25-50 cm thick. One of the cornices triggered a deep slab which slid on the November crust. On Wednesday, a natural size 2 slab was observed on a south aspect at 1800 m which was 100 cm thick. Natural sluffing up to size 2 was reported as well as two cornice failures. One of these triggered a size 3 slab which released down 200 cm. On Saturday, storm slabs are expected to be reactive at higher elevations, especially in wind loaded terrain and on steep convexities. 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 buried weak layers. Click here for more details. Click here for photos of the recent large avalanche cycle.

Snowpack Summary

15-30 cm of new snow overlies a rain crust below around 2000 m 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 cornices are also reported on northerly aspects in the alpine. The rain crust which formed last week is now down 50-60 cm and generally seems to be well bonded to the surrounding snow. The February weak layers are down 120-150 cm and woke up during the recent storm cycle 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 have stepped down to these layers recently resulting in very large avalanches.

Problems

Storm Slabs

Ongoing incremental loading is building slabs which may sit over a rain crust or sun crust. These slabs are most reactive in wind loaded terrain.

Use ridges or ribs to avoid pockets of wind loaded snow.Be alert to conditions that change with elevation.Use caution on steep open slopes and convex rolls

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

Various persistent weaknesses throughout the snowpack create the potential for large avalanches stepping down to buried weak layers. Sustained sun exposure or heavy triggers like a cornice fall could trigger deep, destructive avalanches.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Cornices

Cornices on northerly aspects are large and may become weak during the heat of the day or during a storm.

Cornices become weak with daytime heating. Give cornices a wide berth when traveling on ridges.Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 3

Valid until: Mar 25th, 2017 2:00PM