South Columbia

A bit of new snow and an uptick in wind will feed into existing wind slab problems. Carefully assess wind-drifted snow and lingering buried weak layers if you travel in avalanche terrain.

TUESDAY NIGHT: Cloudy, light flurries with up to 5 cm of snow, moderate northwest wind, alpine temperatures around -15 C.

WEDNESDAY: Mix of sun and cloud, light northwest winds, alpine temperatures around -13 C.

THURSDAY: Increasing cloud, light south winds with moderate to strong gusts in the afternoon, alpine temperatures around -11 C.

FRIDAY: Cloudy, 5-15 cm of snow, light southwest winds with moderate gusts at ridgetop, alpine temperatures around -10 C, freezing level reaching 600 m.

Since Monday, several small to large (size 1-2.5) natural and human-triggered wind slab avalanches have been reported on northerly aspects above 2000 m, breaking 10-50 cm deep. These MIN reports, both from Mt. Brennan on Saturday (here and here), offer helpful examples of this avalanche activity. There continue to be reports of small (size 1-1.5) dry loose avalanches. 

Over the past week the persistent slab problem has produced fewer avalanches than in the first week of February, but is still showing signs of instability and warrants assessment. This MIN report from Joss Mountain on Friday shows that the surface hoar remains reactive on lower elevation cutblock features.  

On Saturday, there was a notable MIN report of a human-triggered wind slab on a southeast aspect in the alpine that stepped-down to deeper persistent weak layers to produce a very large avalanche that ran full path and destroyed mature timber. 

Light flurries have begun to accumulate over a variety of surfaces including surgary facets, feathery surface hoar, and wind-affected snow that formed as a result of last week's dry, cold weather. 5-10 cm of new snow combined with moderate northwest winds may feed into existing wind slab problems, especially in areas with greater accumulation. 

Winds have varied in strength and direction over the past week, loading cornices and forming wind slabs at upper elevations that may still be possible to trigger. Watch for these older wind slabs in unusual places as complicated cross-loading and reverse-loading patterns are prevalent. These wind slabs may overlie weak, sugary, faceted snow, meaning that they could break wider than expected and will likely be slow to bond. 

60-120 cm of snow from February is settling over a weak layer of surface hoar that has shown reactivity at treeline or in "treeline-like" features, like cutblocks, that are below treeline. In steep south-facing alpine terrain, this layer may consist of facets on a sun crust, which has produced notable low probability/high consequence avalanches and requires a conservative approach. Read about managing these conditions in this forecaster blog. 

The mid/lower snowpack is generally strong and settled in most areas.

• Recent wind has varied in direction so watch for wind slabs on all aspects.
• Approach lee and cross-loaded slopes with caution.
• Be aware of the potential for large avalanches due to the presence of a persistent slab.
• Extra caution is needed around cornices under the current conditions.