Avalanche Forecast

Issued: Feb 27th, 2013 10:21AM

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

pgoddard, Avalanche Canada

Sea To Sky.

Danger ratings are based on a very intense storm hitting the coast. There is still some uncertainty around the timing and intensity of this system.

Summary

Confidence

Fair - Timing of incoming weather is uncertain on Thursday

Weather Forecast

A very wet flow (Pineapple Express) is forecast, but exactly when and where the intense precipitation will occur is a matter of uncertainty. Â Thursday-Saturday: Moderate to very heavy precipitation. Strong to extreme SW winds. Freezing level around 1400 m, rising for a time to 1800 m.

Avalanche Summary

Recent reports include several human-triggered slab avalanches to size 2, involving wind slabs, recent storm snow weaknesses and the persistent weakness buried early last week. Some of the avalanches involving the persistent weakness were remotely triggered from as far as 50 m away. A size 3 slab failed naturally on the persistent weakness, wrapping around an entire north-facing bowl and running across a flat bench. A size 2.5 avalanche was triggered by a party of sledders on Sunday in the Brohm Ridge area, and left a man buried 1.8 metres below the surface. The man was successfully rescued.Â Check out theÂ Forecaster blogÂ for the full story.

Snowpack Summary

Incoming snow and wind will add to existing storm slab and wind slab problems, making them deeper and more destructive. A touchy interface of buried surface hoar, facets, and/or a crust, in the upper metre of the snowpack, is a key concern. It appears to be most touchy at treeline and above, but below treeline is not ruled out. It's been triggered on most slope aspects. Remote triggers and wide propagations have already demonstrated the touchiness of this interface. Avalanches triggered in storm snow layers may step down to this weakness, or a deeper interface buried earlier in the month. Cornices are also large and unstable.

Problems

Storm Slabs

Storm snow is expected to become very touchy with continuous loading throughout the forecast period, especially where wind-loaded. Storm slabs may step down to persistent weaknesses, creating very large avalanches

Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>Avoid exposure to overhead avalanche terrain, as large avalanches may reach the end of runout zones.>Give cornices a wide berth when travelling on or below ridges.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 6

Persistent Slabs

Persistent weaknesses buried last week demand respect, as they are very touchy and are causing surprisingly large avalanches.

Be aware of the potential for large, deep avalanches due to the presence of persistent weaknesses.>Avoid exposure to overhead avalanche terrain, as large avalanches may reach the end of runout zones.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

2 - 7

Valid until: Feb 28th, 2013 2:00PM