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Avalanche Forecast

Archived

Feb 22nd, 2023–Feb 23rd, 2023

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

Regions

Lizard-Flathead, South Rockies, Flathead, Lizard, Bull, Elkford East, Elkford West.

Carefully assess for firm, cohesive wind slabs in exposed terrain on all aspects.

Small avalanches on the surface can step down to deeper weak layers, creating large, destructive avalanches.

Confidence

Moderate

Avalanche Summary

A natural avalanche cycle occurred during stormy weather on Tuesday, with numerous storm slab releases up to size 2.5.

Expect surface slabs to remain reactive to human traffic in wind-exposed areas where stiff wind slabs have formed.

Snowpack Summary

Roughly 30 to 40 cm of recent snow and moderate variable winds have formed fresh wind slabs throughout wind-exposed terrain.

The middle of the snowpack is generally well consolidated and sits on a thick crust.

The bottom of the snowpack consists of weak, sugary, basal facets and a crust that is of greatest concern in areas with shallower snow depths, like the Flathead range, Bull river and Elkford areas.

Weather Summary

Wednesday night

Mostly clear / Moderate to strong northeast ridgetop winds / Treeline temperatures -25 to -30 C.

Thursday

Mix of sun and cloud / Moderate to strong northeast ridgetop winds / Treeline temperatures -25 to -30 C.

Friday

Sunny / Light southwest ridgetop winds / Treeline temperatures -20 to -25 C.

Saturday

Sunny / Light to moderate ridgetop winds / Treeline temperatures -15 to -20 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.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

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.

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.