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Avalanche Forecast

Archived

Apr 17th, 2023–Apr 18th, 2023

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

Regions

Purcells, Dogtooth, East Purcell.

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.

Confidence

Moderate

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

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.