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Avalanche Forecast

Archived

Dec 7th, 2022–Dec 8th, 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, Esplanade, Dogtooth, East Purcell.

Reactive wind slabs may exist at treeline and above. Watch and feel for signs of instability such as whumpfing, cracking, and new avalanches.

Concern remains for the persistent weak layers near the base of the snowpack where a small avalanche could possibly 'step down' initiating a larger one.

Confidence

Low

Avalanche Summary

No new natural avalanches were reported on Tuesday. Explosive control in the southern part of the region showed several size 1 dry loose and persistent slabs.

Sunday produced several small (size 1-1.5) persistent slab avalanches from North and Northwest facing treeline. These avalanches failed on the Mid-November surface hoar layer.

We have very few observations from the field. If you do get out please consider reporting in the MIN.

Snowpack Summary

5 to 10 cm of new low-density snow fell by Wednesday. Consistent and strong westerly winds likely redistributed the new and old snow, forming fresh wind slabs in the alpine and treeline. In exposed terrain, some slopes have been scoured back to rock and in sheltered areas, 20-60 cm overlies a generally weak and sugary (faceted) lower snowpack. The prolonged cold temperatures have weakened the generally thin snowpack, promoting faceting as a whole. A buried layer of surface hoar sits 25-60 cm deep and remains a layer of concern, especially once a stiffer slab sits above it.

The overall height of snow is highly variable throughout the region with around 40-150 cm in the alpine.

Weather Summary

Wednesday Night

Cloudy with clear periods. Moderate southwest to westerly winds at ridgetop. Temperatures steady at -15 C.

Thursday

Mix of sun and cloud. Moderate to strong ridgetop wind from the southwest and temperatures slightly warmer near -11 C.

Friday

Mix of sun and cloud with isolated flurries. Light ridgetop wind from the southwest and a daytime high of -11 C and low -15 C.

Saturday

Mostly cloudy with some sunny periods. Trace of new snow. Light southeast winds at ridgetop. ridgetop. Temperatures reach a daytime high of -13 C.

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.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • In times of uncertainty conservative terrain choices are our best defense.

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.