Avalanche Forecast

Issued: Nov 22nd, 2011 9:29AM

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

ccampbell, Avalanche Canada

Sea To Sky.

This bulletin is based on limited data. Local variation in conditions and danger levels are likely to exist. To produce more accurate forecasts, we need information. Please send an email to forecaster@avalanche.ca.

Summary

Confidence

Poor - Track of incoming weather is uncertain on Wednesday

Weather Forecast

Wednesday: The track of the next intense Pacific frontal system is uncertain, but at this point it appears as though it may just miss the Sea-to-Sky region. If this is the case, then expect relatively calm and cold conditions with flurries bringing light amounts of snow accumulation. If the system does hit the Sea-to-Sky region, then periods of very heavy precipitation, strong southwesterly winds, and freezing levels fluctuating between 800m and 1500m, are expected.Thursday: Another intense system is expected to bring 30-40cm with associates strong southwesterly winds and freezing levels around 800m.Friday: A high pressure ridge is expected to dry things out.

Avalanche Summary

Large destructive natural avalanches, triggered by heavy loading from snow and wind, were observed this morning. I expect this natural avalanche activity will continue with additional loading from new snow and wind, and the likelihood of human triggering to remain for the forecast period.

Snowpack Summary

Newly formed surface hoar is now buried by 50-70cm of recent storm snow. Various persistent weaknesses including facets and surface hoar, with an associated crust at upper treeline elevations, can be found down 70-150cm. A deeper crust with associated facets and/or depth hoar is approximately 50cm off the ground.

Problems

Persistent Slabs

Particularly touchy where there is an associated rain crust, which is prominent between 1800m and 2050m. Failure plane for a recent natural avalanche cycle.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

3 - 6

Wind Slabs

Near ridgecrests and terrain breaks, and in cross-loaded gullies. Recent heavy loading from wind resulted in a natural avalanche cycle.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

2 - 5

Storm Slabs

Any open slope with enough snow to smooth out ground roughness. Recent heavy snow loading created a highly unstable situation.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Valid until: Nov 23rd, 2011 8:00AM