There is a real potential for triggering larger-than-expected avalanches as slabs are sitting on a widespread weak layer.
Adopt a conservative approach by sticking to low-angle terrain.
Three weak layers are buried at a prime depth for human triggering within the top meter of the snowpack. With a snowpack such as this, it is important to keep a heads up and know that very small avalanches can quickly become very large. Check out our forecaster blog to learn about how to manage persistent slab problems.
Recent and expected snowfalls are adding depth and load to the reactive storm slab. These storm slabs will remain reactive for longer than “typical” considering it is overlying a widespread weak layer. Human-triggered avalanches are likely where the snowpack varies from thick to thin. Watch for larger-than-expected avalanches, as slabs may step down to deeper layers and result in large avalanches.
Numerous natural and human-triggered storm slabs were observed Wednesday throughout the region. Few natural avalanches ran almost to the valley bottom.
Several natural and very large human-triggered persistent slabs (size 2 to 3) failed on a widespread weak layer underneath the storm snow. Some of them stepped down to deeper buried weak layers and even down to the ground. Many of these human-triggered avalanches were a surprise to the individuals triggering them.
Although natural avalanche occurrences seem to be tapering off, the next round of precipitation may increase the likelihood of triggering. Please continue to share any observations or photos on the Mountain Information Network.
Between 30 and 60 cm of dense storm snow is now sitting on previous surfaces, varying from sugary faceted grains, cold unconsolidated snow or a small surface hoar. At higher elevations, new snow has been redistributed on northerly aspects and fresh slabs may not bond well to older surfaces. At lower elevations, a significant rain crust can be found.
In the upper snowpack, up to three weak layers created earlier in December can be found. Some of these may not exist in all areas of our region. The November weak layer, which will continue to be a concern even after this past storm, can be found anywhere between 75 and 125 cm down. The bottom of the snowpack is generally weak and faceted.
A weak frontal system will push over the interior Thursday. Reinforcements will arrive later Friday as a stronger coastal system will spread moderate snowfalls into the region. Greater amounts are expected in the western sections. Quieter conditions are forecasted for the weekend.
Thursday night
Mostly cloudy, isolated flurries up to 2 cm, southwesterly ridge winds up to 30-40 km/h, treeline temperatures -6 °C. Freezing level around 500 m.
Friday
Snow, generally 5-10 cm except 10-15 cm over the Monashees, southwesterly ridge winds up to 45 km/h, treeline temperatures -5 °C. Freezing level around 500 m.
Saturday
Cloudy, light snowfalls up to 5 cm except 5-10 cm over the Monashees, southerly ridge winds up to 20 km/h, treeline temperatures -5 °C. Freezing level around 500 m.
Sunday
Cloudy, lingering flurries, northwesterly ridge winds up to 20 km/h, treeline temperatures -5 °C. Freezing level around 500 m.
More details can be found in the Mountain Weather Forecast.
