Avalanche Forecast

Issued: Feb 27th, 2013 9:22AM

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

jfloyer, Avalanche Canada

Cariboos.

Difficult and dangerous conditions exist in the backcountry at this time. Choose cautious and conservative routes.

Summary

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain for the entire period

Weather Forecast

Synopsis: Starting Thursday night, a Pineapple Express with a narrow moisture stream has the potential to bring moisture to part or all of this region through the forecast period. Due to the narrow moisture stream, there is poor confidence in snowfall amounts at this time.Thursday: Mostly dry during the day. Freezing level around 1100 m. Winds southwest, mostly light, increasing to strong in the afternoon.Thursday night. 10-15 cm new snow, with the possibility of local enhancement. Very strong SW winds.Friday: Moderate snow/rain (around 10 cm/mm, but heavier amounts possible). Freezing level around 1700 m. Southwesterly ridgetop winds to 80 km/h.Saturday: Moderate snow/rain (around 10 cm/mm). Freezing level around 1600 m. Southerly winds around 30 km/h.

Avalanche Summary

On Tuesday, a very large slab avalanche (size 3.5) was triggered by a cornice collapse on a northeast aspect, with a run distance of 800 m. There were reports of additional natural avalanches up to size 3 (on NE and S aspects) as well as explosive control results up to size 2.5. I suspect the majority of the activity is running on a layer of buried surface hoar from February 12th.

Snowpack Summary

40-70 cm of new snow has fallen in the past few days. Strong west-southwest winds have redistributed the new snow into deep wind slabs on exposed lee slopes and cross-loaded gully features. The February 12 persistent weak layer (crust, and/or surface hoar) is now down 60-80 cm and is primed for triggering. Recent snowpack tests have shown easy to moderate "pops" results on this interface and has been particularly touchy on south aspects where a sun crust exists. Deeper persistent weak layers from early February and late January continue to show planar failures when moderate to hard forces are applied in snow pack tests. These deeper layers have not been reactive to the weight of a rider, but they may be triggered by large loads like an avalanche in motion (step-down avalanche), or a cornice fall.

Problems

Storm Slabs

Expect natural avalanches to run during periods of rapid loading by new snow and wind. Due to the presence of a deeply buried weak layer, the potential size of avalanches could be very large.

Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>Assess start zones carefully and use safe travel techniques.>Stick to simple terrain and be aware of what is above you at all times.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

2 - 6

Persistent Slabs

Additional loading from snow and wind, or the weight of a rider could be enough to trigger the February 12 persistent weak layer.

Choose well supported terrain without convexities.>Stick to simple terrain and be aware of what is above you at all times.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

3 - 7

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