Avalanche Forecast

Issued: Mar 25th, 2017 4:21PM

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

shorton, Avalanche Canada

South Columbia.

Remember snow can lose strength very quickly on sun exposed slopes. Watch for overhead hazards and stick to supported terrain with low consequence.

Summary

Confidence

High - Due to the number and quality of field observations

Weather Forecast

SUNDAY: Sunny in the morning then clouding over around noon, light south wind, alpine temperature around -5 C.MONDAY: Isolated flurries with trace amounts of snow, light southwest wind, alpine temperature around -5 C.TUESDAY: Scattered flurries with another 2-4 cm, light southwest wind, alpine temperature around -5 C.

Avalanche Summary

On Friday, numerous small human triggered avalanches were reported in the top 20-30 cm of storm snow on northerly aspects above 1800 m. Most were size 1-1.5, but a few size 2 slabs were reported as well. Sluffing was reported in steep terrain. Explosive control produced a size 1.5 cornice chunk that did not trigger a slab on the slope below. On Thursday, several size 1.5-2 wind slabs were skier triggered and a natural cornice release triggered two pockets of deep slab in extreme terrain. Explosives triggered 6 cornices up to size 3, but only one these cornices triggered a slab. On Sunday, morning sun is a potential trigger for cornice falls and deeper weak layers. Read the forecasters blog (here) for advice on how to manage this low probability, high consequence scenario and check out the accompanying photos (here). Also expect the recent snow to settle into a slab that will be most reactive at higher elevations, especially in wind loaded terrain and on steep convexities.

Snowpack Summary

20-40 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 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

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

Use conservative route selection, choose moderate angled and supported terrain with low consequence.If triggered, storm slabs or cornices could step down to deeper layers resulting in large avalanchesPay 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 when hit by the sun.

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

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 3

Valid until: Mar 26th, 2017 2:00PM