Avalanche Forecast

Issued: Feb 27th, 2013 9:58AM

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

South Columbia.

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 1200 m. Winds southwest, mostly light, increasing to strong on Thursday afternoonThursday 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 1800 m. Southwesterly ridgetop winds to 80 km/h.Saturday: Heavy snow/rain (around 20 cm/mm). Freezing level around 1900 m. Southerly winds around 30 km/h.

Avalanche Summary

Two large avalanches (size 2 or 3) were remotely triggered from a flat ridge in the Monashees, one on Wednesday and one on Tuesday, both with a fracture depth of 130 cm. In both cases, there was steep north facing terrain directly below the ridge. On Tuesday, there were a good number of natural and human-triggered avalanches on all aspects reported up to size 3, mostly running on the February 12th surface hoar. Natural activity appeared to be triggered either by wind activity (mostly north and east aspects) or during periods of solar activity (southern aspects). Human triggered avalanches were easy and in some cases, surprising.The number, size, and destructive potential of recent avalanche events speak loudly to the touchy nature of the avalanche problem at this time.

Snowpack Summary

Around a metre of storm snow now sits on a highly reactive weak layer of surface hoar layer which was buried on February 12th.The highly variable and destructive nature of this persistent weakness remains a primary concern for professionals in the region. This interface has also shown reactivity on southerly aspects where a sun crust also exists. The mid to lower snowpack layers are generally considered strong and well settled, but a significant period of loading and warming may have the potential to re-activate a more deeply buried layer within the snowpack. Recent and ongoing cornice growth with the current weather pattern is significant, and I expect them to be weak and potentially destructive with anticipated warm weather.

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

3 - 6

Persistent Slabs

Numerous large avalanches are failing on a weak and reactive layer of surface hoar which now lies up to 100cm below the surface. Triggering this weakness may result in large and dangerous avalanches.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

3 - 7

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