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Avalanche Forecast

Archived

Feb 16th, 2023–Feb 17th, 2023

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.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

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

A fatal avalanche occurred west of Golden on February 16th. Details can be found in this report. The snowpack in this region is very complex and requires sophisticated snowpack analysis, careful terrain selection, and extremely diligent group management. The only way to minimize exposure is to select low angle, low consequence terrain and avoid areas where an avalanche could propagate widely. 

Confidence

Moderate

Avalanche Summary

A size 3.5 avalanche that failed on a deep persistent weakness occurred west of Golden on February 16th and resulted in 2 fatalities. More details regarding this avalanche can be found in this report.

Additional avalanches have been reported in the last 48hrs including two size 2 wind slabs on north and east facing alpine features, two size 2 persistent slabs on east aspects above 2300 m, and two cornice failures.

Snowpack Summary

Surface hoar continues to grow in open areas and a sun crust now exists on steep south aspects. Wind slabs of all ages still exist in exposed terrain and windward features are scoured. Good quality, settled powder snow can be found in sheltered alpine and treeline features. Friday could see some new snow fall onto these existing surfaces so pay attention to how that bond develops.

A variety of persistent layers still exists in the middle snowpack and continue to see avalanches occur on them periodically. Don't let these layers surprise you.

The lower snowpack contains a widespread layer of large, weak facets that is typically 80 to 150 cm deep. Snowpack depths at treeline range between 80 and 200 cm, with the shallowest depths found on the eastern edge of the Purcells.

Weather Summary

Thursday night

Increasing cloudiness with flurries bringing 5 cm of new snow. Wind from the southwest at 15 km/h. Temperature -11˚C.

Friday

Cloudy. 5 - 10 cm of new snow. Wind from the southwest at 20 km/h. Temperature -8˚C.

Saturday

Cloudy. 10 cm of new snow. Wind light and variable. Temperature -6˚C.

Sunday

A short clearing in the early morning then cloudy. 5 - 10 cm of new snow. Wind from the southwest 5 - 10 km/h. Temperature -13˚C in the morning rising to -5˚C in the afternoon.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Use careful route-finding and stick to moderate slope angles with low consequences.
  • Avoid rock outcroppings, convexities, and anywhere the snowpack is thin and/or variable.
  • Avoid steep convex slopes.
  • Be especially cautious as you transition into wind affected terrain.

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.

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.