South Columbia

As wind picks up in the alpine Thursday afternoon you need to watch for the formation of fresh wind slabs which will add to the existing wind slab problems. The best riding will be found in wind sheltered areas.  

Southwesterly flow starts setting up to deliver dribs and drabs of snow and a rising freezing level.

WEDNESDAY NIGHT: Freezing level at valley bottom, light north/northwest wind, no snow expected.

THURSDAY: A few clouds at dawn building to broken cloud cover in the afternoon, light southwest wind for most of the day with wind speeds picking up after lunch, trace of snow possible during the day with 1 to 4 cm expected Thursday night.

FRIDAY: Overcast, freezing level rising to about 800 m, light southwest wind at most elevations with some moderate to strong southwest wind at the higher ridgetops, 2 to 10 cm of snow possible during the day with an additional 1 to 5 cm Friday night.

SATURDAY: Overcast, freezing level beginning at valley bottom rising to about 1000 m, moderate to strong southwest wind, trace of snow possible during the day with another 5 to 10 cm Saturday Night.

Avalanche activity has tapered since last weekend. No significant activity to report from Tuesday.

In the adjacent Glacier National Park Region there were some large natural wind slab avalanches reported from extreme north facing terrain features on Monday. A similar natural avalanche from extreme terrain was reported from the southern portion of this region on Monday too.

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. 

The second week of February produced fewer persistent slab avalanches than the first week of February. But, the late January persistent weak layer 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.  

Just a few to as much as 15 cm of snow 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. 

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.