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Avalanche Forecast

Archived

Jan 16th, 2023–Jan 17th, 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.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Purcells, Esplanade, Dogtooth, East Purcell, St. Mary.

Continue to make conservative terrain choices and consider the consequences of an avalanche on a chosen slope. There is variability in the snowpack throughout the region, but what is consistent is that the snowpack is shallower and weaker than average.

Confidence

Moderate

Avalanche Summary

Several small (size 1 to 1.5) slab avalanches were triggered by riders on Saturday and Sunday, as well as some larger size 2 natural slabs on north through east aspects in the alpine. Most of these released on the surface hoar layer from early January. A few large (size 2.5) deep persistent slab avalanches in alpine terrain were triggered naturally and with explosives over the weekend. Also, there was one skier triggered size 2.5 avalanche near Golden on Saturday. This avalanche had a 1 m crown and ran on the facets near the bottom of the snowpack. It was in the alpine on a low angle slope.

Snowpack Summary

Wind slabs may be lingering in alpine terrain and along ridges. Freezing levels have been variable throughout the region with a crust found up to 2000 m in most areas. Up to 15 cm of recent storm snow exists at treeline and above.

There are two concerning weak layers in the top meter of the snowpack. The first is a layer of surface hoar from early January and the second is a layer of surface hoar, facets, and a crust from December. Both these layers are most concerning at treeline and above. There is also a layer of large facets at the bottom of the snowpack that continues to produce avalanches and will likely persist for a prolonged period of time.

In general, the snowpack is shallow and weak.

Weather Summary

Monday night

Cloudy with flurries bringing trace amounts of snow, 20 km/h northwest wind, freezing level drops to valley bottom with treeline temperatures cooling to -8 °C.

Tuesday

Mostly cloudy with the possibility of light flurries bringing trace amounts of snow, 20 km/h west wind, freezing level around 1000 m with treeline temperatures around -5 °C.

Wednesday

Mostly cloudy with light flurries bringing trace amounts of snow, 30 to 40 km/h southwest wind, treeline temperatures around -6 °C.

Thursday

Cloudy with scattered flurries bringing up to 5 cm of snow, 30 km/h southwest wind, treeline temperatures around -6 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Be mindful that deep instabilities are still present and have produced recent large avalanches.
  • 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

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.

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.