Purcells

The past storm snow has added additional weight and stress to a weak and unpredictable layer that remains a concern and undermines the base of the snowpack.

Thin, rocky and steep terrain is the most prominent terrain features that the deep persistent slab has continued to be problematic.

As the freezing level rises and the sun appears, you will find that conditions change drastically through the day.

On Tuesday, Near Invermere, three natural very large (size 3) storm slab avalanches on south east aspects at 2700 m have been reported. These avalanches had significant debris and in some places had scrubbed to ground and are suspect to have failed on the late November deep persistent slab . Explosive control work conducted near Golden produced three storm slab avalanches, these varied in size from small (size 1) to large (size 2). To the west of the region near the Bugaboos, notable very large (size 4) naturally occurring avalanches have been reported on large north facing alpine bowls that went wall to wall and ran peak to creek.

On Monday, near Golden, explosives avalanche control produced a few large (size 2) storm or wind slab avalanches, and one very large (size 3) deep persistent slab avalanche. These avalanches occurred on steep, rocky, sparsely treed ridge features.

West of Invermere, a large (size 2.5), naturally triggered loose wet avalanche was reported that likely started just below treeline, and buried a road cut 2-3 m deep.

On Thursday, north of Golden, just outside of the forecast area, a large (size 2), rider triggered, deep persistent slab avalanche was reported on a northwest aspect in the alpine. The avalanche started 50 m above the riders, and 2 sympathetic avalanches were observed on the adjacent slope. See the excellent Mountain Information Network (MIN) post here for more information, including photos, and reflections on a close call.

15-30 cm of recent snow in the alpine covers settling, dry snow on shaded (northerly) aspects, and a frozen crust on solar aspects. At treeline, the recent snow is likely to be denser, shallower, and moist or refrozen.

Below treeline, rain soaked surfaces are starting to freeze as temperatures drop, and a lot more dirt is showing at low elevations.

The mid snowpack is generally settled and strong, although west of Invermere, some professional operations are still monitoring a layer of weak, feathery surface hoar crystals that was buried in mid January.

The lower snowpack includes a widespread layer of large, weak facets and/or depth hoar crystals. This weak layer has been responsible for several very large and destructive avalanches throughout the season, including one last Thursday.

Overnight cooling followed by afternoon rising freezing levels and warming is likely to unconsolidated and rapidly settle the upper snowpack especially on south aspect terrain when the sun appears. Prepare to continually evaluate the conditions, and change plans as necessary.

Wednesday Night

Clear with some clouds. Trace amounts of snow. Freezing level descending to 300m, Alpine temperature low of -10°C. Light to moderate northwest ridgetop wind.

Thursday

Clear with some clouds. Trace to 5cm of snow.. Freezing level rising to 1600m mid day. Alpine temperature high of -1. Light northwest wind.

Friday

Clear with some clouds. Trace of new snow. Freezing level rising to 1700m mid day. Alpine temperature high of -1°C. Light northwest wind.

Saturday

Clear and sunny with no forecast precipitation. Freezing level rising to 1800m mid day. Alpine temperature high of 0°C. Light to moderate southwest wind.

More details can be found in the Mountain Weather Forecast.

• Continue to make conservative terrain choices while the storm snow settles and stabilizes.
• Be alert to conditions that change throughout the day.
• Be alert to conditions that change with aspect and elevation.
• Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.