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Avalanche Forecast

Archived

Dec 7th, 2022–Dec 8th, 2022

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 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

South Rockies, Bull, Crowsnest North, Crowsnest South, Elkford East, Elkford West.

Reactive wind slabs may exist in the treeline and the alpine. Watch and feel for signs of instability such as whumpfing, cracking, and recent avalanches.If you seek more sheltered areas at treeline you should consider that this is where the persistent slab has been most reactive in snowpack tests. Keep your terrain choices conservative and assess conditions while you travel.

Confidence

Low

Avalanche Summary

On Tuesday no new natural avalanches were reported but visibility was limited. Skier-controlled dry loose avalanches up to size 1 were seen. They ran in the recent storm snow and no deeper.

Last weekend, explosive control produced a large size 2.5 wind slab avalanche on a southeast aspect in the alpine. This avalanche gouged down to the faceted lower snowpack in its track and as a result, entrained a large amount of mass.

Looking forward, I suspect wind slabs will be reactive at upper elevations.

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

Snowpack Summary

Up to 15 cm of new low-density snow fell across the region by Wednesday morning. The new snow accompanied by changing winds (strong from the NW and now switching to the WSW) and slightly warming temperatures may form fresh and reactive wind slabs in the alpine and at treeline. This snow overlies a previously heavily wind-affected surface in open areas and many windward slopes may have been stripped back to early-season layers or rock.

30-60 cm of snow sits on top of a weak interface comprising of surface hoar and facets which showed reactivity in snowpack testing. The lower snowpack is sugary and faceted with a rain crust near the ground.

Total snowpack depths at treeline elevations are 50-80 cm.

Weather Summary

Wednesday Night

Dribs and drabs overnight. Westerly winds 50-60 km/h at ridgetop. Temperatures are steady near -12 C.

Thursday

Cloudy with isolated flurries. Southwesterly winds 50-80 km/h at ridgetop. Temperatures slightly warming to -8 C and freezing levels valley bottom.

Friday

Mostly cloudy with light snow 5-10 cm. Strong to extreme southwest winds at ridgetop. Temperatures steady near -10 C.

Saturday

Cloudy with 5 cm of new snow. Southwest winds are generally light with moderate to strong gusts at ridgetop. Treeline temperatures reach a high of -12 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.
  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.

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.