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Avalanche Forecast

Archived

Mar 4th, 2022–Mar 5th, 2022

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.

Regions

Kootenay Boundary.

A frozen crust in the upper snowpack is bad news. Travel conditions could be very challenging. If there is new snow on top of the crust, it could slide easily, and slide far. 

Clear skies will improve the view, but avalanches will be more likely on sunny slopes.

Confidence

High - We have a good understanding of the snowpack structure and confidence in the weather forecast

Weather Forecast

Friday Night: Mostly clear. No new snow expected. Light north wind. Cold air pooling in valley bottoms, making for a short-lived temperature inversion. Alpine low around -5 °C.

Saturday: Mostly Sunny. No new snow expected. Light north wind. Freezing level rising to 1500 m through the day. Alpine high around -3 °C.

Sunday: Sunny. No new snow expected. Light northeast ridgetop wind, trending to moderate in the high alpine. Freezing level at valley bottom overnight, rising to 1500 m through the day. 

Monday: Mostly cloudy. Moderate northwest ridgetop wind, trending to extreme in the high alpine. Freezing level at valley bottom overnight, rising to 1500 m through the day. 

Avalanche Summary

On Friday, south of Nelson, natural loose wet avalanches were reported up to size 1.5 in the afternoon on steep solar aspects. Also, east of Kelowna, a natural windslab avalanche and several explosive triggered windslabs were reported up to size 1.5 on east through south aspects around treeline. 

Additionally, east of Slocan (in the neighboring South Columbia region), a snowmobile triggered size 2 avalanche was reported, no other details at this time. 

On Thursday, south of Nelson, avalanche control with explosives triggered several small to large avalanches, failing below through the crust that formed on Wednesday.

On Wednesday, several natural and explosive triggered storm slabs up to size 2 were reported across the region. Also, a professional operation west of Trail reported a large natural loose wet avalanche below tree line that scoured to ground, and ran to the end of the path, 550 m long. 

Snowpack Summary

5-20 cm of new snow sits on a 1-5cm rain crust that goes as high as 2200 m in some parts of the region. There are a few great Mountain Information Network posts that describe the challenging backcountry travel conditions on Thursday due to this crust. 

Some places in the Kootenay Boundary have received over 60 mm of water over the course of the storm that started in the last few days of February. That has translated to about 20-50 cm (depending on elevation) of settled snow. This recent storm snow sits on a variety of hard surfaces, and feathery surface hoar crystals in some locations.

Weak layers from mid-February and late January made up of crusts and/or surface hoar crystals can be found around 60-70 cm deep. There are not a lot of recent avalanches on these layers, but they are still on the radar of operators in the area.

Terrain and Travel

  • A crust on the surface will help bind the snow together, but may make for tough travel conditions.
  • Closely monitor how the new snow is bonding to the crust.
  • Be alert to conditions that change with elevation.
  • Use small low consequence slopes to test the bond of the new snow.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.

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.

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.