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Avalanche Forecast

Archived

Mar 14th, 2023–Mar 15th, 2023

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

Regions

Purcells, Dogtooth, East Purcell, West Purcell.

Storm snow and strong southwest winds have created dangerous avalanche conditions at alpine and treeline. Use extra caution when transitioning into wind affected terrain, where storm slabs remain reactive to human triggering.

Avoid thin, rocky, wind effected areas where triggering slabs is more likely. If triggered storm slabs may step down to deep weak layers resulting in large destructive avalanches.

Confidence

Moderate

Avalanche Summary

On Sunday, good visibility revealed a widespread natural avalanche cycle from within the storm. Numerous storm slab and wind slab avalanches were observed on all aspects in the alpine and at treeline, up to size 2.5. Three natural deep persistent slab avalanches were observed in the Golden area, size 2.5-3, in steep, rocky terrain at 2400m.

If you head out in the backcountry, let us know what you are seeing by submitting a report to the Mountain Information Network.

Snowpack Summary

15-30 cm of storm snow is being redistributed by southwest winds. Storm snow overlies a plethora of surfaces including wind-affected surfaces in open areas, surface hoar and facetted snow in sheltered areas and a sun crust on steep solar slopes.

Buried surface hoar sits 70-90 cm deep in sheltered terrain features, and a thin sun crust exists at the same depth on steep south-facing terrain. Several other layers from January can also be found in the top 100cm of the snowpack.

The lower snowpack is made up of a widespread layer of large, weak basal facets and depth hoar in some areas. this weakness has been responsible for a number of recent very large, destructive avalanches and will continue to be a concern.

Weather Summary

Tuesday Night

Mainly clear skies. Alpine temperatures reach a low of -10 °C. Ridge wind southwest 15 km/h. Freezing levels drop to valley bottom.

Wednesday

Mainly cloudy with sunny periods and isolated flurries, trace accumulation. Alpine temperatures reach a high of -4 °C. Ridge wind northwest 20 km/h gusting 35 km/h. Freezing levels rise to 1300 meters.

Thursday

Sunny. Alpine temperatures reach a high of -2 °C. Ridge wind variable 15 km/h. Freezing levels rise to 1400 meters.

Friday

Sunny. Alpine temperatures reach a high of -2 °C. Ridge wind southerley 20 km/h. Freezing levels rise to 1600 meters.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Be especially cautious as you transition into wind affected terrain.
  • Surface hoar distribution is highly variable. Avoid generalizing your observations.
  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Avoid areas with a thin or variable snowpack.

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.

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.

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.