Avalanche Forecast

Issued: Mar 24th, 2017 3:45PM

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

South 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 size 1.5 storm slab was observed on a NW aspect at 2450 m as well as solar triggered sluffing up to size 1.5 from steep sun exposed slopes. A natural cornice release triggered two pockets of deep slab in extreme terrain. A skier remotely triggered a size 2 wind slab from 20 m away on a north aspect at 2100 m. Skiers also triggered three size 1.5-2 wind slabs on northeast through southeast aspects between 2400 and 2800 m elevation. Explosives triggered six cornices up to size 3 but only one these cornices triggered a slab. On Wednesday, a natural size 2 was reported on a south aspect. A skier triggered a size 1 storm slab on a north aspect at 2200 m which was 15-25 cm thick. 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 40-50 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 caution on steep open slopes and convex rollsBe alert to conditions that change with elevation.Use ridges or ribs to avoid pockets of wind loaded snow.

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 avalanches stepping down to buried weak layers. Sustained sun exposure or heavy triggers like a cornice falling could trigger deep, destructive avalanches.

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

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.

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

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 3

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