Regions
Kootenay Boundary.
Confidence
Fair - Due to variable snowpack conditions
Weather Forecast
The KB will start to see some precipitous action as a Surface Low develops out of the front over the Southern Interior Monday. The KB should see a bit of snow starting Sunday night. I expect 10 cm Sunday evening, an additional 10 Monday during the day and then 5 – 10cm of light density snow Monday evening. High pressure builds in Tuesday which should result in quite a bit of solar & cooler (seasonal) temps.FZLVL:Mon: Starts near 1500m, lowering to the surface by Tuesday AMTue: SurfaceWed: Starting near the surface, rising as high as 1500 in the afternoon, returning to Surface overnight.Wind: Mon: Mod SW, switching NW overnight. Strong to Extreme SW at ridgetop.Tue: L, NE at all elevations.Wed: Mod W/NW ridgetop winds strong NW.
Avalanche Summary
Two significant human triggered avalanches occurred on Thursday, before we had much wind or significant warming. 1. A group of sledders triggered a size 2.5 avalanche below treeline near 1700m in a moderately angled cutblock, resulting in a full burial. That same day, a snowboarder in the Nelson backcounty triggered a size 3.0 avalanche below treeline, SE aspect, 84cm in depth, 400m wide, running full path to the valley bottom. The snowboarder was able to cut out of the slide early and was unharmed. On Friday a group remote triggered a size 2.5 avalanche from 30m away on a SE facing slope near 2000m in the Slocan. The crown depth was 90cm, failing on the early Feb. SH. On Saturday ski cutting produced numerous soft slabs with crowns 10 - 40 cm in depth.
Snowpack Summary
Sunday was a very warm day in the mountains, Stagleap Wx station at 2140m reached -0.9 C Sunday at 11:00. This warmth has changed the character of the supper snowpack, allowing it to settle into a more cohesive slab. There are two problem layers to watch; A. The Feb. 29 interface which consists of surface hoar on shady aspects and a thin sun crust on south aspects. B. Surface hoar buried mid-February, which is now down 70-120cm and still giving sudden snowpack test results. There will likely be 10cm of fresh Monday morning when we wake up, and an additional 10cm during the day Monday which will do a great job of hiding the cohesive slab beneath.We often think about cold temperatures “locking things up.” Tuesday dawns cold & clear, but 20 – 25 cm of new light density snow will insulate 100cm of very warm snow that rests on the mid Feb SH. With this structure in place, we’ll need to give the snowpack some extra time to adjust. Continue to stay conservative in your terrain selection Monday & Tuesday, the surface hoar problem is far from over.
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.
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.
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.