A special avalanche warning has been issued that includes the South Coast Inland. A buried surface hoar layer in the south of the region remains reactive and may persist for longer than usual. For further details see: http://goo.gl/JDfMjZ
Confidence
Poor - Due to the number of field observations
Weather Forecast
A weak storm system reaches the South Coast late Friday or early Saturday morning. Around 10mm of precipitation are expected for much of the region on Saturday. Freezing levels should peak at around 1000m and alpine winds are expected to be moderate-to-strong from the NW. A ridge of high pressure builds on Sunday and will persist for several days. Sunday should be mostly clear and dry with freezing levels around valley bottom and light alpine winds. Monday should be pretty much the same with colder temperatures.
Avalanche Summary
We haven't received any reports in a few days. If you are out in the mountains, please consider sending us your observations or posting on our website. On Wednesday we received a report on whumphing in the Coquihalla area. On Monday we received a report of storm slabs up to size 2.5 being remote-triggering from flat areas up to 75m away in the Coquihalla area between 1600 and 1900m elevation. Slabs were 40-70cm thick and were releasing on the surface hoar layer. Natural activity is not expected on Friday but human triggering remains possible.
Snowpack Summary
A persistent slab sits above the mid-December surface hoar layer. In the north of the region the slab is around 30-40cm thick and in the south it is 50-80cm. The surface hoar appears to be quite reactive at treeline and possibly into the lower parts to the alpine, especially where it was sheltered from wind. Reports suggest that it is most reactive in the Coquihalla and Allison Pass areas. About 10cm below the surface hoar layer is a thick rain crust the extends to around ridgetop elevation. Strong SW winds have created wind slabs in exposed alpine terrain which may still be a concern.
Problems
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.