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Avalanche Forecast

Archived

Feb 3rd, 2021–Feb 4th, 2021

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

Regions

Northwest Inland.

A persistent weak layer of surface hoar, facets and a crust is buried 30-60 cm down. This avalanche problem is less obvious and harder to predict, so conservative terrain choices are best.

Fresh wind slabs may also be reactive on leeward slopes. 

Confidence

Low - Forecast snowfall amounts are uncertain. Uncertainty is due to whether buried persistent weak layers become active, triggering avalanches, with the arrival of the forecast weather.

Weather Forecast

Wednesday Night: Snow amounts 5-15 cm. Alpine temperatures near -7 and freezing levels at the valley bottom. Ridgetop wind 30-60 km/hr from West.

Thursday: Mix of sun and cloud. Alpine temperatures near -3 and freezing levels near 1100 m. Ridgetop wind light-moderate from the West.

Friday/ Saturday: Mix of sun and cloud. Alpine temperatures near -12 and freezing levels at the valley bottom. Generally light but gusty winds from the west-northwest.

Avalanche Summary

On Tuesday, reports of a widespread loose dry avalanche cycle occurred in the Babine region. These avalanches were up to size 2 and ran in steep terrain on all aspects and elevations. Wind slabs were also reactive to skier triggers up to size 1 on southwest aspects in the alpine. 

With new snow and wind persistent slabs and wind slabs will likely be reactive on Thursday. 

Snowpack Summary

Up to 10 cm of new snow fell by Tuesday afternoon bringing 20-40 cm of accumulative low-density storm snow from the past week over a variety of old snow surfaces. These old surfaces include surface hoar in locations sheltered from the wind at all elevations, surface facets, and stiff wind affected snow. On solar aspects, a buried sun crust can be found and a thick crust exists near the surface below 1000 m. Additional snow and wind combined with cohesion may stress these potentially weak interfaces, creating the persistent slab problem.

The lower snowpack has two decomposing crust layers that have been driving a deep persistent slab problem for most of the past month, however, no notables have been reported in the past 2-3 weeks. The upper crust is 70-140 cm deep and continues to show occasional hard sudden results in snow pits. The deeper crust at the bottom of the snowpack is more prevalent in shallow snowpack ranges. These layers seem to be dormant under the current conditions, but shallow rocky slopes should still be carefully assessed and approached with caution. 

Terrain and Travel

  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Watch your sluff: it may run faster and further than you expect.

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.