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Avalanche Forecast

Archived

Mar 15th, 2023–Mar 16th, 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.

Watch for hazard increasing during peak daytime heating. Natural avalanches are possible and human-triggered avalanches are likely.

Avoid thin areas like rock outcroppings where you are most likely to trigger deep persistent layers.

Confidence

Moderate

Avalanche Summary

On Tuesday, 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. 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 overlies wind-affected snow in open areas, facetted snow in sheltered areas and a thin 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

Wednesday Night

Few clouds clear through the night. Alpine temperatures reach a low of -10 °C. Ridge wind northwest 20 km/h gusting 30 km/h. Freezing levels drop to valley bottom.

Thursday

Mix of sun and cloud. Alpine temperatures reach a high of -4 °C. Ridge wind west 15 km/h. Freezing levels rise to 1500 meters.

Friday

Mainly sunny. Alpine temperatures reach a high of -3 °C. Ridge wind southwest 20 km/h. Freezing levels rise to 1600 meters.

Saturday

Sunny. Alpine temperatures reach a high of -2 °C. Ridge wind southwest 15 km/h. Freezing levels rise to 1700 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.
  • Be alert to conditions that change with elevation and sun exposure.
  • 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.

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.