Avalanche Forecast
Issued: Mar 5th, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Storm Slabs.
bchristie,
Avalanche Canada
Choose your terrain carefully, and use extra caution near ridgecrests, and shallow or rocky start zones. A frozen crust could make backcountry travel difficult. The crust is breakable, and you could still trigger an avalanche deeper in the snowpack.
Summary
Confidence
Moderate - We have a good understanding of the snowpack structure and confidence in the weather forecast Uncertainty is due to how quickly the snowpack will recover and gain strength.
Weather Forecast
Saturday Night: Clear. No new snow expected. Light to moderate north ridgetop wind. Freezing level falls to valley bottom. Alpine low around -7 °C.
Sunday: Sunny. No new snow expected. Light northwest ridgetop wind, trending to moderate at higher elevations. Freezing level rising to 1500 m through the day. Alpine high around -5 °C.
Monday: Partly cloudy. No new snow expected. Moderate northwest ridgetop wind, trending to extreme in at higher elevations. Freezing level at valley bottom overnight, rising to 1600 m through the day.Â
Tuesday: Increasing cloud through the day. 2-5 cm of snow expected. Light, variable ridgetop wind. Freezing level stays at valley borrom, alpine temperature around -10 °C.
Avalanche Summary
On Saturday, south of Nelson, small loose wet avalanches were reported on solar aspects. No other reports before 4 pm.
On Friday, south of Nelson, a large, remotely triggered slab avalanche was reported on a northeast aspect around treeline. The avalanche was triggered by a snowmobile, and it started on a steep, rocky, unsupported slope near a ridgetop. Also south of Nelson, natural loose wet avalanches were reported up to size 1.5 in the afternoon on steep solar aspects. 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.Â
Additionally, east of Slocan (in the neighboring South Columbia region), a snowmobile rider triggered a size 2 slab avalanche on a northeast aspect around treeline. They were partially buried and injured. More details and photos here. The same group also remote triggered another avalanche on a solar aspect from 50 m away.Â
On Thursday, south of Nelson, avalanche control with explosives triggered several small to large avalanches, failing below the crust that formed on Wednesday.
Snowpack Summary
5-20 cm of new snow sits on a 1-5cm rain crust that goes as high as 2250 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.Â
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 60-100 cm deep. Some recent persistent slab avalanches on this layer have surprised riders, so keep this type of avalanche in mind when making terrain choices.
Terrain and Travel
- Approach steep, open and/or sparsely treed slopes cautiously.
- Avoid steep convexities or areas with a thin, rocky, or variable snowpack.
- Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
- 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.
Problems
Persistent Slabs
Weak layers from February (mostly crusts and surface hoar) are likely down around 60 cm and may become more reactive as the overlying snow settles into a denser slab. Two weak layers of surface hoar from January are likely down 100 cm or more and are primarily a concern in the east half of the region on northerly aspects around treeline.
A 1-5 cm thick crust that formed in early March could make it more difficult to affect these layers with the weight of a human or snowmobile, BUT if you aren't feeling the crust underneath you, or if you feel like your turns are digging in below it, choose simpler terrain and give avalanche terrain a wide berth. Remote triggered avalanches have been recently reported on this layer.
Diligent terrain selection is required for this type of avalanche problem. Signs of instability may not be visible on the surface, and the resulting avalanches will be large. An important part of your strategy would be to avoid rocky start zones below ridgetops and convex rolls.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Storm Slabs
Human triggering of storm slabs should remain on your radar. Thursday night's snow is settling into a denser slab, and it may slide easily on the underlying crust that has been reported as high as 2250 m.
Test the bond of new snow on smaller terrain features with low consequences as you travel through various elevation bands and aspects.
If you don't find a crust on or near the surface, or if you easily break through the crust, it will be possible to trigger avalanches deeper in the recent storm snow.
Cornices have grown during the last system as well so give them a wide berth.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Mar 6th, 2022 4:00PM
