Avalanche forecast

Northwest Inland

Feb 16 – 17, 2021Avalanche Canada
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Avalanche danger

Thu
Fri
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Moderate northwest wind will form fresh wind slabs in alpine and treeline lee terrain features. Older wind slabs can be found on all aspects and elevations. Cold temperatures preserved the weak bond of the wind slabs and they may continue to be susceptible to human triggering. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Moderate northwest wind will form fresh wind slabs in alpine and treeline lee terrain features where soft snow is available for transport. Wind slabs will be especially susceptible to human triggering where stiff and punchy feeling snow sits on top of weak faceted crystals.

    The wind direction shifted from the recent strong outflow winds to westerly and now to northwest. During the strong outflow winds steep, lee westerly aspects have been the most reactive. The shifting winds have created wind slabs on multiple aspects and all elevations. Older wind slabs might also be present in open terrain pockets at treeline and below treeline. Cold temperatures preserved the weak bond between the slab and the weak faceted crystal layer underneath. These wind slabs may still be triggered by humans and propagate wider than expected.

Confidence

Moderate - Uncertainty is due to the extreme variability of wind effect on the snowpack.

Weather Forecast

MONDAY NIGHT: Cloudy, trace of new snow, moderate northwest wind, temperature low -12 C.

TUESDAY: Mostly cloudy, trace of new snow, moderate northwest wind, temperature high -10 C.

WEDNESDAY: Mix of sun and cloud, trace of new snow, moderate northwest wind, temperature high -7 C.

THURSDAY: Mostly cloudy, strong southeast wind, temperature high -9 C.

Avalanche Summary

Wind slabs have been reactive to human triggering in wind loaded and cross loaded features. Most ski cut results have been of size 1 to 1.5, but bigger terrain features could propagate wider and produce larger avalanches! On Saturday hard wind slabs were easy to trigger in the Crater Lake area as evidenced by this MIN.

In the Babine area a field team noted numerous size 1-2 wind slabs in the alpine on Saturday from the past 36 hours. They also posted this MIN from the Onion. This is in line with other avalanche observations from the outflow wind cycle like this size 2 near Miller Creek.

In the southwest of the region, two natural cornice triggered avalanches of size 2.5 and size 3 were reported on Friday and Sunday. They probably released during the outflow wind cycle.

Check out this forecaster MIN post from Microwave from Thursday to see the widespread wind effects. 

Snowpack Summary

Small amounts of new snow have fallen on hard slabs, scoured slopes and sastrugi where outflow effects have been the strongest. In sheltered areas, the cold temperatures are encouraging surface faceting. The late January interface is down 30-50 cm consisting of isolated surface hoar in sheltered locations, and previous wind affected layers in exposed areas. On solar aspects, a buried sun crust can be found in places as well.

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

  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

Regions covered