Avalanche Forecast
Issued: Apr 17th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs, Deep Persistent Slabs and Loose Wet.
lbaker,
Avalanche Canada
At upper elevations, where the dry snow sits on a crust, persistent slabs have been propagating widely, are surprisingly deep, and could be triggered by warmth, cornices, or riders.
Remain cognizant that a weak, unpredictable layer continues to lurk near the bottom of the snowpack, avoid thin, rocky start zones and shallow areas with variable snowpack depths.
Check for signs of windslab avalanche danger like shooting cracks, especially near ridgetops and in cross loaded gullies.
Summary
Confidence
Avalanche Summary
On Sunday, small natural loose wet avalanche activity was reported on slopes impacted by the afternoon sun.
On Saturday, a widespread natural slab avalanche cycle was observed and reported. These avalanches were very large up to (size 3) and are suspected to be storm snow than ran on a crust buried in early April.
A fatal avalanche occurred on April 15 in the Thunderwater Lake riding area, just west of this region. The avalanche was triggered near a rocky area and was very large (size 3). Two riders were caught, one was buried approximately 2 meters deep. Despite an immediate extrication rescue response, the rider did not survive. Any additional information we have on this accident can be found in this MIN.
If you are getting out in the backcountry, consider making a post on the MIN (Mountain Information Network). You can share riding conditions, avalanche or snowpack observations, or even just a photo or two.
Snowpack Summary
At treeline and above, 15-40 cm of recent snow fell with moderate to strong southwest wind, forming windslabs in leeward terrain and storm slabs. A variety of crust, surface hoar and/or facet layers that were buried in mid March through early April may exist in the upper snowpack. Recent avalanche activity in adjacent regions indicate that these interfaces contributed to the current avalanche problem there. Most professional operations in the forecast area are tracking their own local layer of concern to see if they become active with increasing temperatures, or more load from new rain or snow.
Below treeline, expect to find moist or refrozen surfaces, and shrinking snowpack depths.
The mid snowpack is generally settled and strong, although west of Invermere, some professional operations are still monitoring a layer of weak, feathery surface hoar crystals that was buried in mid January.
The lower snowpack includes a widespread layer of large, weak facets and/or depth hoar crystals. This weak layer has been responsible for several very large and destructive avalanches throughout the season, including one last Thursday.
Weather Summary
Monday Night
Mostly clear. Light, gusting moderate, southeast ridgetop wind. Freezing levels remain around 1300 m. Treeline low around -5 °C.
Tuesday
Partly cloudy with scattered flurries beginning late afternoon flurries, 5 - 10 cm accumulation. Light southeast ridgetop wind switch to west in the afternoon. Freezing levels rise to 1700 m. Treeline high around 0 °C.
Wednesday
Cloudy with sunny periods and isolated flurries, trace accumulation. Light northwest ridgetop wind. Freezing levels rise to 1600 m. Treeline high around -1 °C.
Thursday
Mix of sun and cloud. Light northwest ridgetop wind. Freezing levels rise to 1900 m. Treeline high around 0 °C.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Be especially cautious as you transition into wind affected terrain.
- Be alert to conditions that change with aspect and elevation.
- Watch for unstable snow on specific terrain features, especially when the snow is moist or wet.
- Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
Problems
Persistent Slabs
15-40 cm of dry snow in the alpine and overlies a variety of crust complexes that have been reactive in adjacent regions.
Moderate to strong south and southwest winds have built deeper, more reactive pockets of windslab in leeward terrain.
Use extra caution around ridgecrest, small rolls, and on convex slopes. Retreat to mellower terrain if you find signs of instability like shooting cracks, whumpfs, or recent avalanches.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
The base of the snowpack remains very weak. Avoid thin, rocky start zones and shallow areas with variable snowpack depths.
Deep persistent slab avalanches continue to be reported in this forecast area.
This is a low-probability/high-consequence avalanche problem, and managing it is very tricky.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Loose Wet
During daytime periods of warming and direct sun effect on the snow surface, the loose wet avalanche problem will become increasingly sensitive to triggering.
Aspects: South East, South, South West, West.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Valid until: Apr 18th, 2023 4:00PM
