Avalanche Forecast

We seem to be in the doldrums for the next few days with a bit of snow possible Thursday night.

MONDAY NIGHT: Freezing level at valley bottom, light northwest wind, trace of snow possible. 

TUESDAY: Broken cloud covert, freezing level at valley bottom, moderate northwest wind, trace of snow possible.  

WEDNESDAY: Broken cloud covert, freezing level at valley bottom, moderate northwest wind, trace of snow possible.  

THURSDAY: Clear skies at dawn building to overcast in the afternoon, freezing level at valley bottom, light south wind at most elevations with ridge top wind increasing late in the afternoon. No snow anticipated during the day. A few cm possible Thursday night.

On Sunday natural and explosive triggered wind slabs size 1 to 2 were reported from northwest, north, northeast and east facing features between 1900 and 2300 m. MIN reports from Sunday indicate that there was quite a bit of whumphing which is a clear sign of instability.

A bout of sustained strong east and northeast winds prompted widespread wind slab formation and reactivity on Friday and to a slightly lesser extent on Saturday. Many 20-50 cm-deep slabs released naturally, with skier triggering and with explosives on Friday, some with remarkably wide propagation. Having formed over weak, faceted grains, these wind slab hazards may persist for quite a bit longer than usual.

We also have many reports in from last week of persistent slab avalanches triggered by skiers at elevations around treeline (1800-2000 m) where a persistent weak layer exists as surface hoar. Check out the 7-day MIN for more details. Persistent slab avalanche activity has been on the decline more recently, but subtle factors like diminishing slab properties and savvy terrain use may account for this trend. Professionals in the region continue to highlight persistent slabs as an ongoing concern.

Another explosives-triggered persistent slab in the Bonningtons last Tuesday stepped down to our early December crust layer to produce a 200 cm-deep, size 3.5 (very large!) avalanche. A similar avalanche (size 3.5, step down to December crust) occurred naturally in the same area in the first week of February.

A strong wind event last weekend has left widespread wind slabs and heavily wind effected snow in it's wake. These wind slabs rest on weak faceted snow that developed during the cold snap. 

The upper snowpack continues to settle over another weak layer buried 60-80 cm deep (from January 24). This persistent weak layer may exist as facets or a crust but it has been most reactive where it exists as large surface hoar crystals in steep, sheltered areas at treeline and below. This layer is slow to gain strength and requires careful terrain selection, even as its likelihood of triggering gradually diminishes.

There are several more layers of surface hoar in the mid snowpack, with the most notable one down about 80-120 cm, buried in early January. These older layers (or the crust described below) may take precedence over the layers described above in shallower snowpack areas from the Nelson Range through to the Okanagan.

Another widespread crust from early December is surrounded by weak faceted grains and buried deep within the snowpack. It may be possible to trigger this layer with a large load in a shallow rocky start zone.

• Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
• Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.
• If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
• Use caution on large alpine slopes, especially around thin areas that may propagate to deeper instabilities.