Weather patterns are divided across the the region: a clearing trend is forecast for the north, continued precipitation is expected on the Coquilhalla. Avalanche danger will be locally higher in areas that continue to receive heavy snowfall and wind.
Weather Forecast
The north of the region will see a clearing trend over the next couple of days while moderate snowfall will continue through tomorrow in the Coquihalla.Tonight and Monday: Moderate snow locally in the south, dry in the north / Winds moderate to strong westerly / Freezing level 1300mTuesday: Cloudy / Winds moderate to strong westerly / Freezing levels to rise as high as 2500m.Wednesday: Cloudy / Winds light westerly / Freezing levels 2500m
Avalanche Summary
We have receive reports of a a widespread natural avalanche cycle with numerous large to very avalanches. Some reports indicate isolated avalanches are failing down on the old facet layer just above the ground.
Snowpack Summary
While the storm has passed in the North, local snowfall continues in the Coquihalla.The weekends storm clobbered the region with between 80-100cm of new snow now. Sustained moderate to strong south to southwest winds have created thick and reactive winds slabs. In the north of the region, the storm snow fell onto a week layer of surface hoar from earlier in the month. In areas with a shallow or rocky snowpack facets exist immediately above the ground. Although from the surface things are starting to look more normal for the coast, it is important to remember that the storm snow is sitting on a thin and weak midpack. The "wait 48 hours and you're good" Coastal mantra does not apply as these conditions are likely to persist for some time.These persistent weak layers do not seem to be as prevalent in the south where the early season snowpack was deeper and less affected by early December's cold temperatures.Snowpack depths at treeline range from 150-250 cm in the south of the region, and from 90- 150 cm in the north of the region. In glaciated terrain open and poorly bridged crevasses are everywhere although they are now hiding under a meter of unsupportive storm snow.
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.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.