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Avalanche Forecast

Archived

Mar 16th, 2023–Mar 17th, 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.

The possibility of triggering a deep persistent slab avalanche remains the main concern. The sun packs a punch this time of year, so minimize your exposure during peak daytime warming.

Confidence

Moderate

Avalanche Summary

On Wednesday there were still reports of a few natural and explosives triggered storm and wind slab avalanches to size 2 and 3 which were suspected of having stepped down to deeper layers of facets.

On Tuesday there was a widespread natural avalanche cycle. Numerous storm slab and wind slab avalanches were observed on all aspects in the alpine and at treeline, up to size 2.5. Three naturally triggered size 2.5-3 deep persistent slab avalanches were observed in the Dogtooth range running in steep rocky terrain. Evidence of a size 4 natural deep persistent slab avalanche was observed in the western Purcells.

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 wind-affected storm snow falling earlier in the week overlies wind-affected snow in open areas, facetted snow in sheltered areas and a thin sun crust on steep solar slopes.

Buried surface hoar can be found 70-90 cm deep in sheltered terrain features. A thin sun crust exists at the same depth on steep south-facing terrain.

The lower snowpack is made up of a widespread layer of large, weak facets and/or depth hoar crystals. This weak layer has been responsible for a number of recent very large, destructive avalanches and will continue to be a concern.

Weather Summary

Thursday Night

Cloudy with clear periods. Treeline temperature -7 °C. Wind light southwest.

Friday

Mainly sunny. Treeline temperature -2 °C. Wind light southwest. Freezing level rising to 1600m.

Saturday

Mainly sunny. Treeline temperature -1 °C. Wind light southwest. Freezing level rising to 1700m.

Sunday

Mainly sunny. Treeline temperature 0 °C. Wind light southwest. Freezing level rising to 1800m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Be especially cautious as you transition into wind affected terrain.
  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.
  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Avoid areas with a thin or variable snowpack.
  • If triggered, storm slabs in-motion may step down to deeper layers and result in very 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.

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.