North Columbia

Another day of yellow! Though avalanche occurrences are becoming less frequent, the possibility of triggering persistent slabs still exists, and the consequences are high. A cautious approach to backcountry travel is recommended.

High -

THURSDAY NIGHT - Mainly cloudy with isolated flurries / southwest winds 15-30 km/h / alpine low temperature near -13FRIDAY - Cloudy with scattered flurries, up to 10 cm / southwest winds 10-20 km/h / alpine high temperature near -10SATURDAY - A mix of sun and cloud with isolated flurries / northeast winds 10-15 km/h / alpine high temperature near -11SUNDAY - A mix of sun and cloud / northeast winds, 10-15 km/h / alpine high temperature near -15

On Wednesday, several natural loose and wind slab avalanches to size 2 were reported. There were also reports of 3 persistent slab avalanches between size 2-2.5. These occurred on south and southeast aspects at alpine and treeline elevations. Two were natural and one was triggered remotely (from a distance) by a person.Over the past week there have been daily reports of both natural and human triggered wind slab avalanches, between size 1-2. There have also been near daily reports of persistent slab avalanches, some of which are still being triggered by humans. These are in the size 2-3 range and are likely failing on the persistent weak layer that was buried mid January. This layer is discussed at more length in the Snowpack Summary below. While reports of avalanches on this persistent weak layer are becoming fewer and further between, they carry high consequences.

Up to 10 cm of new snow is expected to fall throughout the day on Friday with moderate southwest winds, which will likely form wind slabs in lee terrain.The new snow will fall on 10-25 cm of older snow, which has also been blown into wind slabs in many areas. These older wind slabs may exists on all aspects due to variable wind directions, and they may become difficult to detect with the new snow on top of them.There are two prominent weak layers in the upper snowpack. One was buried at the end of January, and the other was buried mid January.  They are approximately 40 and 75 cm below the surface. Both layers consist of a mix of surface hoar (feathery crystals) and facets (sugary snow), which likely also sit on a sun crust on south facing slopes. These weak layers are most prominent at treeline and below treeline, though south facing slopes at any elevation are suspect as well.Very sporadically, failures have occurred near the base of the snowpack in this region, or in neighboring regions. These releases have almost all been from high alpine areas, possibly triggered close to rocky features.