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Avalanche Forecast

Archived

Feb 4th, 2021–Feb 5th, 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 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.

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. 

Confidence

Low - Uncertainty is due to whether buried persistent weak layers become active, triggering avalanches, with the arrival of the forecast weather. Uncertainty is due to the limited number of field observations.

Weather Forecast

Friday: Cloudy with isolated flurries. Alpine temperatures near -6 and light to moderate wind from the west-northwest. Freezing levels at valley bottom.

Saturday: Snow 10-15 cm. Alpine temperatures near -10 and ridgetop wind moderate to strong from the northeast. 

Sunday: Mix of sun and cloud. Alpine temperatures falling to a low of -21 and a high of -14. Ridgetop wind light from the northeast. 

Avalanche Summary

No new reports on Thursday. 

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 additional snow and wind, persistent slabs and wind slabs may be reactive to skier and rider triggering on Friday. 

Snowpack Summary

Up to 15 cm of new snow fell by Thursday afternoon bringing 20-40 cm of accumulative 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. 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 deep persistent 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

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • 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

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.