Regions
Northwest Coastal.
A storm has ramped up avalanche danger throughout the region. Travel in avalanche terrain is not recommended.
Weather Forecast
Saturday night: The tapering storm will deliver another 10-15 cm in the overnight period. Winds strong from the southwest. Sunday: Mainly cloudy with scattered flurries bringing another 5 cm of new snow. Winds moderate to strong from the west. Freezing level to about 900 metres with alpine temperatures around -2. Monday: Mainly cloudy with isolated flurries and a trace of new snow. Winds light to moderate from the northwest. Freezing level dropping to 300 metres with alpine temperatures around -8. Tuesday: A mix of sun and cloud. Winds light to moderate from the northeast. Freezing level to valley bottom and alpine temperatures around -10.
Avalanche Summary
Our storm is unfortunately obscuring visibility of higher elevation terrain where the bulk of avalanche activity is expected to be ongoing. With that said, explosives control in the Stewart area on Friday yielded numerous storm slab results results to Size 2 with crown depths of 25-60 cm. Numerous loose wet avalanches have also been reported at highway elevations. Avalanche size and frequency is expected to increase as snowfall continues to accumulate. Aside from slab avalanche concerns, it should also be noted that loose wet avalanches can be expected to continue running out of steep terrain at lower elevations.
Snowpack Summary
A storm impacting the region over Friday and Saturday has delivered approximately 40-90 cm of new snow to the mountains, with the greatest depths accumulating in coastal areas. Strong to extreme southwesterly winds have accompanied the storm and lower elevations are seeing precipitation fall as rain. Snow will continue to fall over Saturday night and by Sunday morning me might expect anywhere from 70-130 cm to have accumulated above above the latest buried surface hoar layer from January 23rd. This surface hoar was previously reported growing up to size 10 mm at treeline and below and may be associated with a crust below 1100 metres. Although storm slab problems have captured our attention, there continue to be several other surface hoar layers of concern from early January and Christmas. Some reports show these persistent weak layers to be rounding and bonding, however recent reports show sudden planar releases in snowpack tests with hard forces applied. Our ongoing heavy precipitation will be a good test for these older buried weak layers.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
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.