Avalanche Forecast

Issued: Mar 22nd, 2017 3:53PM

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

rbuhler, Avalanche Canada

South Columbia.

Thursday's danger will be driven by the amount of sun you get in your local area. When the sun is out in full strength, expect natural avalanches including the potential for large persistent slabs. Conservative terrain selection remains critical.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain on Thursday

Weather Forecast

Another 5-10 cm of snow is expected Wednesday overnight with moderate to strong alpine wind from the southwest and freezing levels at 1200-1500 m. A mix of sun and cloud is expected on Thursday with light to moderate alpine wind from the southwest and freezing levels reaching around 1500 m in the afternoon. 5-10 cm of snowfall is forecast for Friday with moderate southwest wind in the alpine and freezing levels reaching 1500 m or so in the afternoon. Similar conditions are forecast for Saturday with light snowfall, moderate alpine wind, and freezing levels reaching around 1500 m in the afternoon.

Avalanche Summary

On Tuesday, a ski cut triggered a thin size 1 storm slab on a north aspect at 2000 m. Explosives triggered a size 2.5 cornice which cleaned out the slope below. On Monday, a natural cornice release triggered a size 1.5 wind slab on a north aspect at 2500 m and a natural size 2 storm slab was observed on a southeast aspect at 2200 m. Four natural size 2.5-3 wind slabs were also observed on southeast and east aspects at 2250-2400 m. Explosives triggered a deep persistent slab on a northeast aspect that released up to 2 m deep. Over the weekend, a widespread avalanche cycle occurred with avalanches up to size 4.5. This included very large cornice releases, avalanches releasing on layers near the base of the snowpack, propagations over 1 km wide, and mature timber being broken. Click here for photos of the recent avalanches.On Thursday, sun is expected to drive the hazard. If there is are long periods of strong sun, expect sluffing from steep sun exposed slopes, cornices will become weak, and persistent slab avalanches could fail naturally. With the recent avalanche activity and several weak layers within snowpack waking up, it is a time to be very conservative with terrain selection.

Snowpack Summary

10-25 cm of new snow overlies a thick rain crust which formed over the weekend. The crust has been reported up to around 2000 m and has been reported to be supportive to skiers between 1500 and 1900 m. Alpine wind has recently been strong from a variety of directions and has formed wind slabs on all aspects. 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 100-150 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 stepped down to these layer recently resulting in very large avalanches.

Problems

Persistent Slabs

Various persistent weaknesses throughout the snowpack create the potential for large step down avalanches. Sustained sun exposure or heavy triggers like a cornice fall could trigger a deep and destructive avalanche.

Use conservative route selection, choose moderate angled and supported terrain with low consequence.Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.If triggered, wind slabs or cornices could step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Wind Slabs

Recent wind has been from a variety of directions and wind slabs should be expected in exposed terrain on all aspects at higher elevations. Cornices on northerly aspects are reported to be large and weak.

Use caution in lee areas. Recent wind loading has created wind slabs.Use ridges or ribs to avoid pockets of wind loaded snow.Be alert to conditions that change with elevation.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

1 - 2

Loose Wet

If the sun is out in full strength, expect natural sluffing from steep sun exposed slopes.

Avoid steep sun exposed slopes when the solar radiation is strong.Be cautious of sluffing in steep terrain.Watch for clues, like sluffing off of cliffs, that the snowpack is warming up.

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

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Mar 23rd, 2017 2:00PM