Confidence
Fair - Intensity of incoming weather is uncertain
Weather Forecast
The Purcells do quite well with regard to snowfall for the next few days. The region should pick up 4 – 8cm Sunday evening and an additional 3 – 5cm Sunday night. MON: A surface low develops over the Southern Interior Monday which should bring an additional 10 – 15 cm. TUE: High pressure builds in Tuesday which should result in quite a bit of solar & cooler (seasonal) temps. Winds increase late in the day out of the W/NW near ridgetop. WED: The pattern looks very similar to last week. Freezing levels should be on the rise, but, a ridge of high pressure off the coast of California is shielding the region from moisture.FZLVL:Mon: 500m, lowering to the surface by evening.Tue: SurfaceWed: Starting near the surface, rising as high as 1700 in the afternoon.Wind: Mon: L SW, switching NW late in the day with frontal passage. Strong to Extreme W at ridgetopTue: L, NE at all elevations.Wed: Mod W/NW ridgetop winds strong NW.
Avalanche Summary
Control work in the Dogtooth range produced numerous slab avalanches to size 1, crowns 5 - 20cm in depth. With all the new snow & wind I suspect there was some natural activity, although we probably won't know the extent of it until skies clear Tuesday. There are two great observations from professionals working in the region recently. The first one can be found on the MCR, it talks about the widespread & sensitive nature of the SH in the Northern Purcells. You can start here and work your way into the March observations:https://www.acmg.ca/mcr/archives.aspThe other is in the form of a youtube video which also deals with the surface hoar, highlighting the potential for remote triggering and large propagations when this layer fails. Check out the shooting cracks in the video. Wild!:https://www.youtube.com/watch?v=UmSJkS3SSbA&feature=youtu.be
Snowpack Summary
A cohesive slab continues to settle over the mid-February surface hoar, which is generally down in the 65-75cm range. Recent reports include whumpfing and cracking, and moderate but sudden compression test results. This persistent weakness is susceptible to remote triggering and has the ability to propagate in low angled terrain, and the overlying slab structure creates the potential for step-down avalanches. Basal facets have only been reactive on steep, shallow, and rocky slopes, but operators continue to monitor this layer in tests. Triggering this deep persistent weak layer is unlikely, but shallow snowpack areas or shallow weak areas adjacent to deeper wind loaded slopes are the most suspect locations.
Problems
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.
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.
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.