Avalanche Forecast

Issued: Mar 23rd, 2017 3:59PM

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

cgarritty, Avalanche Canada

Kootenay Boundary.

New snow and wind will be building avalanche hazard over the course of the day on Friday. Keep aware of the changing conditions.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain on Friday

Weather Forecast

Friday: Cloudy with flurries bringing 10-15 cm of new snow over the day. Moderate to strong south winds. Freezing level to 1600 metres with alpine temperatures of -2.Saturday: Mainly cloudy with isolated flurries and a trace to 5 cm of new snow. Light southwest winds. Freezing level to 1500 metres with alpine temperatures of -3Sunday: Cloudy with sunny periods. Light south winds. Freezing level to 1700 metres with alpine temperatures of -2.

Avalanche Summary

Reports from Wednesday showed our recent snow accumulations triggering naturally as loose moist sluffs from Size 1-2 below treeline. The recent snow also reacted to ski cutting and small cornice releases at higher elevations, producing Size 1 results. Reports from Tuesday indicated snowballing and loose snow avalanches to size 1 from steep terrain on all aspects from tree line and below.Looking forward, similar activity can be expected on Friday as new snow accumulates, wind redistributes it into reactive wind slabs, and rising freezing levels promote loose wet activity at lower elevations. Meanwhile, the lingering possibility of persistent slab reactivity continues to demand a more cautious approach to terrain selection in the alpine.

Snowpack Summary

Last weekend rain soaked the upper snowpack for a second time in a week all the way to mountain tops. Subsequent cooling temperatures then formed a 10-30cm rain crust. In many parts of the region above the 1500m there may now be 15-20cm of new snow sitting on top of the crust. Below the crust expect to see moist or wet snow. The late-February facet / surface hoar interface (70-120 cm deep), the mid-February crust (90-130 cm deep), and basal facets in shallow snowpack areas may still be present at upper elevations and may still be reactive and become a concern as surface crusts break down with daytime warming.

Problems

Wind Slabs

Forecast new snow and moderate to strong winds will form touchy wind slabs in the lee of exposed terrain features at higher elevations. This problem will be increasing over the course of the day on Friday.

Use caution in lee areas at treeline and above. New snow and wind will be creating wind slabs.Use ridges or ribs to avoid pockets of wind loaded snow.If triggered, wind slabs may step down to deeper layers and result in large avalanches.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

At upper elevations where the recent rain crust is not as thick and strong, there is still potential to trigger deeper buried weak layers. A smaller wind slab release could be the perfect trigger.

Pay attention to overhead hazards like cornices which could easily trigger deep slabs.Be aware of thin areas that may propogate to deeper instabilites.Be alert to conditions that change with elevation.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Loose Wet

As the freezing level rises to around 1600 metres, surface snow below this elevation will become increasingly moist and may begin to sluff from steep terrain. This may happen naturally as well as with skier traffic.

Be cautious of sluffing in steep terrain.Avoid travelling on ledges and cliffs where sluffing may have severe consequences.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Mar 24th, 2017 2:00PM