Confidence
Fair - Freezing levels are uncertain on Friday
Weather Forecast
Tuesday night into Wednesday: Snow amounts near 5cms overnight with 5-10cms during the day. Ridgetop winds switching from the SW to the NW 20-30km/hr. Freezing levels valley bottom. Thursday: High pressure building over the province today will bring dry conditions. Freezing levels will remain valley bottom for most of the day. May elevate in the afternoon. Ridgetop winds will blow from the North 30-40km/hr. Friday: Dry conditions. Warm air and rising freezing levels will persist into Saturday. Ridgetop winds switch, light-moderate values from the SW.
Avalanche Summary
Several size 3 natural slab avalanches were reportedly seen on Monday. These occurred on NE aspects, suspect instabilities could haven been light to moderate loading above treeline producing slab avalanches from specific terrain features. Explosive avalanche control done in the Dogtooth Range produced 2 avalanches up to size 2, running full depth to ground basal facets. These were on NW-N aspects, at 2300m. On Sunday observations include one large size 3.5 slab avalanche that occurred west of Invermere at 2300m on a SE-SW aspect, 600m wide, running 1300m in length, and the slab pulled out to the ground basal layers.
Snowpack Summary
The Purcell's are one of the more complex & variable snow packs in the province right now.The storm over the weekend delivered 20 - 40 cm of snow to the region with moderate gusting strong winds out of the SW, S & a bit of SE. This snow fell on a snow pack that is for the most part, pretty well settled.There are a few exceptions though: The Jan. 13th SH/FC combo has been reactive in ski hill testing, but this needs to be taken with a grain of salt as this snowpack is a bit artificial when compared to a true backcountry uncontrolled snowpack. Regardless, I feel like we can't take our eyes off this layer just yet, remember, it's only two weeks old.It sounds like there is a lot of strong snow over the mid December facet layer which is buried approx. 80 cm on the east side and 200+ cm on the west side. This layer seems to have more energy in the Purcells than any other region in the province and was reactive on Jan. 28th, when a skier remotely triggered a size 3 avalanche. This seem to be a low probability high consequence situation.There are basal facets at the ground which remain a concern, especially on Northerly aspects at high elevations. Snowpack depths at 2000m sit near 2m deep.
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.