Avalanche Forecast

Issued: Jan 19th, 2017 4:56PM

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

Avalanche Canada shorton, Avalanche Canada

The recent storm produced many large avalanches. Human triggering will remain likely in the upcoming days and warrants a cautious approach to terrain.

Summary

Confidence

High - Due to the number and quality of field observations

Weather Forecast

FRIDAY: Cloudy with gradual clearing, light southwest winds, freezing levels dropping with alpine temperatures around -5 C.SATURDAY: Cloudy, moderate southeast winds, alpine temperatures around -5 C.SUNDAY: Mix of sun and cloud, light southeast winds, alpine temperatures around -5 C.

Avalanche Summary

On Wednesday, widespread natural avalanches were reported throughout the region. These included size 2 storm slabs and size 2-3 persistent slab avalanches releasing on old surface hoar layers. Loose wet avalanches were reported out of steep terrain below 1200 m. Natural avalanche activity will taper off with the dry and cool weather, but human triggering of storm and persistent slabs will remain likely.

Snowpack Summary

40-60 cm of storm snow in the south of the region has been transported by strong southwest winds in the alpine and at treeline over the past few days. The freezing level has been around 1200 m, and below this level the snowpack is moist or wet. As the storm snow settles into a slab, we are concerned that several of the weak surface hoar or facet interfaces that developed during cold and clear weather may become reactive. The January 5th layer is down 50-80 cm, and the December 25th layer is now down close to 100 cm in deeper snowpack areas. These are not typical conditions for this coastal region, and it may take some time to gain confidence about the distribution and likelihood of triggering these deeply buried weak layers. Areas exposed to cornice fall should be avoided due to the possibility of a cornice triggering a deep weak layer. I suggest a conservative approach to terrain while gathering info after the storm.

Problems

Storm Slabs

An icon showing Storm Slabs
Natural storm slab activity may end as the storm snow settles, however human triggering may continue to be likely. Avoid large slopes with convexities, and any slope exposed to overhead hazards like cornices.
The new snow will require several days to settle and stabilize.If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2 - 3

Persistent Slabs

An icon showing Persistent Slabs
It's still possible to trigger avalanches on buried weak layers (Dec 25, Dec 30, Jan 5th, Jan 12th surface hoar) ... or have a smaller avalanche 'step down' and trigger deeper instabilities.
Be aware of thin areas that may propogate to deeper instabilites.Use conservative route selection, choose moderate angled and supported terrain with low consequence.Be aware of the potential for wide propagations.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Jan 20th, 2017 2:00PM

Login