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Confidence
Fair - Intensity of incoming weather is uncertain on Saturday
Weather Forecast
Continued unsettled, stormy weather conditions through the South Eastern parts of the province. A strong SW flow, moderate snowfall amounts and rising freezing levels will prevail. Thursday: Snow amounts 10-20 cm. Ridgetop winds strong from the SW. Treeline temperatures near 2 degrees. Freezing levels 1800 m. Friday/Saturday: Snow amounts light-moderate. Ridgetop winds will remain strong from the SW. Freezing levels 1800 m, falling to 1200 m on Saturday.
Avalanche Summary
On Tuesday explosive controlled avalanches up to size 1.5 were reported. On Monday, skiers triggered size 1-1.5 soft slabs in steep terrain. A widespread natural avalanche cycle occurred up to size 3 in response to very warm temperatures and loading of start zones by strong winds on Friday and Saturday. Video footage here: https://bit.ly/yR4E8r . On Friday, a snowmobiler was killed in a size 3 slab on a south-west aspect at treeline in the Corbin Creek area and a skier was injured in an avalanche in steep terrain in the Flathead Range. Over the last week, there were several reports from in or near the region of near misses, including a snowmobiler who triggered an avalanche and was buried for around 30 minutes, remote-triggered avalanches, and slab avalanches running into unusually low-angled terrain. With forecast snow, wind and warming; I expect the region will see another natural avalanche cycle.
Snowpack Summary
Recently the region has received 30-40 cm of new snow. Touchy storm slabs exist at all elevations. Strong SW winds have created stiff wind slabs behind ridges and terrain breaks. The mid February surface hoar layer in the upper snowpack is most prevalent in the west and south of the region, particularly in the Flathead. Recent snowpack tests, as well as rider-triggered avalanches, on this weak layer indicate that it still has the potential to be triggered in many areas, resulting in a large destructive avalanche. Remote-triggering, triggering from below and triggering on low-angled terrain are also concerns. Basal facets may still exist, particularly in shallower snowpack areas with steep, rocky start zones. Cornices have grown large and threaten slopes below. Conditions are variable across the region.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.