Avalanche Forecast

Issued: Feb 23rd, 2012 9:29AM

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

Avalanche Canada swerner, Avalanche Canada

Summary

Confidence

Fair - Intensity of incoming weather is uncertain

Weather Forecast

An approaching low pressure system will bring light-moderate precipitation to the NW regions Thursday night through to Saturday. Friday: Snow amounts 10-15cm through the day. Ridgetop winds 30km/hr from the SE. Treeline temperatures near -7. Freezing levels 500m. Saturday: Light snowfall amounts. Ridgetop winds light-moderate from the SE. Freezing levels remain at valley bottom. Sunday: A ridge of high pressure will bring dryer, cold conditions.

Avalanche Summary

Recently submitted near Smithers, on Mt. Evelyn's South face was a size 3 slab that was skier triggered. This was on a SE aspect@ 1800m. The report indicates a wind loaded slope. For more details visit the link below. On Tuesday a size 2.5 and a size 2 natural slab avalanches were reported. These occurred in the western part of the region, on E-S aspects @ 1700, 1400m. The 2.5 ran 900m in distance. I'd be very cautious right now. With more snow and wind forecast, I suspect the mid-February buried surface hoar layers will become reactive creating dangerous avalanche conditions. Please visit this link to view full details of an avalanche report submitted today. http://www.avalanche.ca/cac/library/incident-report-database/view/360158b8-5627-4c4b-8726-c25bde927f18

Snowpack Summary

About 25 cm of snow that fell over the past week sit on a variety of old surfaces. These surfaces include: melt-freeze crusts that exist on all aspects at lower elevations and on south-facing slopes higher up and well-settled powder on shaded aspects in the alpine. Weak surface hoar crystals (size 3-4mm) are sandwiched between the old surfaces and the newer snow and have recently shown easy compression test results. The distribution of the surface hoar seems to be up to treeline on all aspects and on sheltered features in the alpine. This upper snow pack structure will be the big thing to watch as the overlying slab develops. I expect to see increasing reactivity in the surface hoar interface. The mid and lower snowpack are generally well settled and strong.The warning signs are clear and a large avalanche cycle has started in the Interior BC regions. I suspect with forecast weather, and similar weak layers in the snowpack, the NW Inland may start to see an avalanche cycle. Please read our Special Avalanche Warning, and visit our Forecaster's Blog for more detailed information.

Problems

Persistent Slabs

An icon showing Persistent Slabs
Forecast snow and wind will increase the soft slab load on the variable buried weak layers. I suspect this to be a concern as these layers reach their "Tipping Point" where natural and human triggered avalanche activity will increase.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 6

Wind Slabs

An icon showing Wind Slabs
Increasing winds and new snow through the forecast period will form wind slabs on lee slopes and terrain features. Expect to see reverse loading due to changing winds.

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 6

Valid until: Feb 24th, 2012 8:00AM

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