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Avalanche Forecast

Archived

Jan 28th, 2023–Jan 29th, 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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Purcells, Dogtooth, East Purcell, West Purcell.

The snowpack is thin and weak, with several buried weak layers of concern. Find the newest blog here for managing this weak snowpack.

Small avalanches, even wind slabs, have the potential to trigger larger avalanches deeper in the snowpack. Continue to choose low consequence terrain, avoiding terrain features capable of producing large avalanches.

Confidence

Moderate

Avalanche Summary

Numerous skier triggered and natural wind slabs were reported throughout the region on east facing slopes throughout the last three days.

A few notable avalanche occurred on Wednesday, where small wind slabs 'stepped down' to deeper weak layer causing large avalanches.

On Tuesday there was a report of a size 3.5 natural avalanche in the Dogtooth Range. This was likely a deep persistent avalanche with a wide propagation triggering near ridgetop at the upper end of treeline on an easterly aspect.

On Monday there was a size 3 skier triggered a deep persistent avalanche on an east aspect starting at 2300 m in the Terminator area in the Dogtooth Range. This MIN outlines the avalanche.

Snowpack Summary

Up to 10 cm of wind affected new snow has buried wind affected surfaces, a small layer of surface hoar and a sun crust.

The mid-snowpack contains a couple of layers of major concern. The first is down 30 to 50 cm and is a layer of surface hoar from early January. The second is a layer of surface hoar, facets, and crust created in December and found 40 to 60 cm down. The surface hoar is most prevalent in sheltered areas while crusts with faceted snow are more widespread.

The bottom of the snowpack is weak and faceted and contains a weak layer from late November. Thin snowpack areas where weak layers sit closer to the surface should still be treated as suspect.

The total depth of this weak and shallow snowpack ranges between 80 and 180 cm at treeline and is shallowest in the eastern part of our region.

Weather Summary

Saturday Night

Mostly clear skies overnight with trace accumulations possible. Moderate northeast winds. Freezing levels below valley bottom.

Sunday

Sunny with no snowfall expected. Moderate northerly winds continue, alpine high temperatures of -16°C.

Monday

Sunny with increasing afternoon cloud. Winds switch to moderate (gusting strong) westerlies. Alpine high of -16°C.

Tuesday

A mix of sun and cloud. Trace accumulations of snowfall. Moderate westerlies. Alpine high of -12°C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Uncertainty is best managed through conservative terrain choices at this time.

Problems

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.

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.

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.