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Avalanche Forecast

Archived

Dec 17th, 2022–Dec 18th, 2022

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

Regions

Purcells, Dogtooth, East Purcell.

Be aware that if triggered, avalanches may step down to deeper layers resulting in large, destructive avalanches. Keep your terrain choices conservative, as temperatures fall even a small accident can have big consequences.

Confidence

Moderate

Avalanche Summary

On Thursday and Friday explosive control produced wind slab avalanches up to size 2 on north aspects. One of which stepped down to the mid november layer.

Persistent slab activity has died down over the past week but in the neighboring central Columbia region, where it is buried deeper, this layer continues to produce rider triggered avalanches up to size 2.5

Snowpack Summary

Up to 10cm overlies variable surfaces ranging from hard old wind slabs in exposed features at upper elevations to soft, unconsolidated facets in sheltered areas.

A concerning weak layer composed of surface hoar, facets and/or a crust that formed in mid November is now buried 40 to 80cm deep. Avalanche activity on this layer has tapered off but it is likely still possible to trigger this layer in isolated terrain features at treeline.

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

Weather Summary

Saturday Night

Scattered flurries bringing 5cm of new snow. Light southwest wind. Low of -18 at 1800m.

Sunday

Scattered flurries bringing up to 5cm of new snow. Light southerly wind. High of -19 at 1800m.

Monday

A mix of sun and cloud with no new snow expected. Light southwest winds and a high of -22 at 1800m.

Tuesday

A mix of sun and cloud with no new snow expected. Light westerly winds and a high of -26 at 1800m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid open slopes and convex rolls at and below treeline where weak layers may be preserved.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • In times of uncertainty conservative terrain choices are our best defense.

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.