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Avalanche Forecast

Archived

Mar 18th, 2023–Mar 19th, 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 possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Purcells, Dogtooth, East Purcell, West Purcell.

Natural avalanche activity will be driven by solar input on Sunday. Minimize your exposure to steep slopes facing the sun during the hottest part of the day.

Stick to thick snowpack areas where you are less likely to trigger deep weak layers.

Confidence

Moderate

Avalanche Summary

On Friday, a few solar-triggered loose dry avalanches were reported in the region to size 2. A natural size 2.5 windslab, likely triggered by the sun, was observed on a southwest aspect at 2500 m.

Explosives control triggered a deep persistent slab avalanche, size 2.5, on an east aspect at 2350m

If you head out in the backcountry, let us know what you see 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. A sun crust is found on the surface of solar slopes at all elevations.

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

Saturday Night

Clear skies. Treeline temperature -6 °C. Wind light northwest. Freezing levels drop to valley bottom overnight.

Sunday

Sunny. Treeline temperature -1 °C. Wind light southeast. Freezing level rising to 1900m.

Monday

Mix of sun and cloud. Treeline temperature -2 °C. Wind light east. Freezing level 1800m.

Tuesday

Mix of sun and cloud. Treeline temperature -4 °C. Wind light variable. Freezing level 1600m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.
  • Avoid areas with a thin or variable snowpack.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.