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Avalanche Forecast

Archived

Dec 22nd, 2022–Dec 23rd, 2022

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

Regions

Purcells, Dogtooth, East Purcell.

Assess exposed slopes for wind slab. Strong winds will likely redistribute the loose surface snow into new wind slabs.

Confidence

Moderate

Avalanche Summary

On Tuesday and Wednesday explosive control in the region produced only very small avalanches with a depth of 10cm.

If you are headed into the backcountry please consider filling out a Mountain Information Network report.

Snowpack Summary

Southwest winds will likely form new wind slabs on north and east aspects. These slabs will form over a layer of facets meaning they will not bond well. As winds reach the strong range wind slabs could form lower down slope than expected.

The main layer of concern is the mid-November layer, which is made up of either surface hoar, facets, or crusts. It is now buried 40 to 80 cm deep. Avalanche activity on this layer has tapered off but it could still be possible to trigger this layer in isolated terrain features near treeline.

Alpine snowpack distribution is variable, with depths ranging from 70 to 140 cm.

Weather Summary

Thursday Night

Light flurries bringing trace amounts of new snow. Moderate southwest winds and a low of -29 at 2000m.

Friday

Cloudy with up to 5cm of new snow expected. Strong southwest winds and a High of -25 at 2000m.

Saturday

Cloudy with flurries bringing up to 5cm of new snow. Strong southwest winds and a high of -20 at 2000m.

Sunday

A mix of sun and cloud with flurries bringing trace amounts of new snow. Moderate southwest winds and a high of -14 at 2000m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • 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.

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.

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.