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Avalanche Forecast

Archived

Feb 26th, 2021–Feb 27th, 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 and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Northwest Inland.

Reactive wind slabs will be the primary concern on Saturday. The natural avalanche cycle may have tapered off, however; slopes may continue to be primed and waiting for skier and rider triggering. 

Confidence

Low - Uncertainty is due to the limited number of field observations. Uncertainty is due to field data and reports showing a wide variation in conditions throughout the region.

Weather Forecast

Yet another approaching Pacific warm front will unleash Saturday through Monday. This will bring strong to extreme wind, rising freezing levels, and some fresh snow.

Saturday: Flurries in the afternoon. Ridgetop wind strong from the southwest and alpine temperatures near -2. Freezing levels rising 900 m.

Sunday: Snow 5-20 cm. Ridgetop wind extreme. Freezing levels 1000-1200 m. 

Monday: Mix of sun and cloud with some flurries. Ridgetop wind moderate from the southwest and alpine temperatures near -5. Freezing levels valley bottom.

Avalanche Summary

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. 

For the weekend, I suspect wind slabs to 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

20-30 cm of new snow fell Thursday. This arrived with strong to extreme southwest to northwest wind building fresh and reactive wind slabs and storm slabs on wind-sheltered slopes. 

This brings 40 to 60 cm of snow which overlies 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, suggesting 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

  • 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.

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.