Avalanche forecast

Northwest Inland

Feb 28 – Mar 1, 2021Avalanche Canada
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Avalanche danger

Tue
Wed
Alpine
4 · High
Treeline
4 · High
Below
3 · Considerable
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Highlights

Fresh and reactive wind and storm slabs will build overnight Saturday and through Sunday. These slabs could step down to a deeper weak layer resulting in larger avalanches. Its a good time to be extra conservative, avoid avalanche terrain and overhead wind-loaded slopes.

Avalanche problems

  • Wind Slabs

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

    Cranking southwest wind and new snow have formed fresh new wind slabs. Changing winds from the northwest will add to the complex loading pattern. Wind slabs may be found on most aspects at upper elevations and may be more reactive where they overlie weak surfaces formed mid-February, potentially including weak surface hoar and/or faceted grains. 

    Large looming cornices exist. Be diligent and give them a wide berth from above and below. Fragile cornices may fail due to extreme wind and warming tempertures on Sunday.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2.5

    There is anywhere from 40 to 80 cm of snow above a mixed bag of old snow surfaces including hard wind pressed snow, sugary facetted snow, feathery surface hoar in sheltered locations that were buried in mid-February. A lot of uncertainty surrounds this interface and it may be reach the threshold with additional snow and wind forecast. The primary concern now is wind or storm slab avalanches stepping down to this layer and skier or rider triggering which would result in a large, consequential avalanche. 

Confidence

Moderate - Forecast snowfall amounts are uncertain. Uncertainty is due to the extreme variability of wind effect on the snowpack.

Weather Forecast

The dominating feature associated with this next frontal system will be WIND. Ridgetop wind is forecast 40-80 km/hr from the southwest through the forecast period. Snowfall amounts are harder to pin down.

Saturday Night: Snow amounts 5-20 cm. Ridgetop wind strong from the southwest and alpine temperatures near -3. Freezing levels 700 m.

Sunday: Snow 5-20 cm accompanied by strong wind from the southwest. Alpine temperatures near 0 and freezing levels 1300 m.

Monday: Cloudy with light snow 5 cm. Ridgetop wind moderate to strong from the southwest. Alpine temperatures near -6 and freezing levels 500 m.

Tuesday: A mix of sun and cloud and light snow up to 5 cm. Ridgetop wind moderate to strong from the southwest. Alpine temperatures near -6 and freezing levels 600 m. 

Avalanche Summary

No new avalanche reports on Saturday.

On Friday, fresh natural reactive wind slabs up to size 2 were reported from the alpine on E-NE aspects. 

On Thursday, numerous audible avalanches were reported in the southwestern part of the region, and an ongoing avalanche cycle was noted. This area received heavier snowfall amounts up to 30 cm so a lot of variability across the region. Sluffing of the new snow occurred in steep terrain features. 

On Sunday wind slabs may be the primary concern, however; in parts of the region that receive more than 20 cm of fresh snow, storm slabs may also be a factor. Natural avalanche activity may taper but skier and rider triggering is likely. 

Snowpack Summary

New wind slabs will form overnight and through Sunday. In wind-sheltered areas, new storm slabs may build. Forecast snowfall amounts vary across the region, so some areas may only see fresh wind slabs and some areas may see a more widespread storm slab problem. Regardless, the snowpack will likely be unstable and reactive Sunday. The new snow will add to the 20-30 cm of snow that fell Thursday. This arrived with strong to extreme southwest to northwest wind and brings 40 to 80 cm of snow sitting on a variety of old snow surfaces consisting of hard wind-affected snow in exposed terrain and weak, faceted snow or surface hoar crystals in sheltered terrain. It may take some time for the snow to bond to these surfaces.

Basal faceted snow remains part of the snowpack structure in much of the region. Once we see a substantial warm-up, we'll be thinking about the potential for the reactivation of basal layers.

Terrain and Travel

  • Avoid all avalanche terrain during periods of strong wind.
  • Choose conservative terrain and watch for clues of instability.
  • 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