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Avalanche Forecast

Archived

Mar 1st, 2021–Mar 2nd, 2021

Alpine
Natural avalanches possible, human triggered probable.
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 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.

Strong southwest wind will howl on Tuesday building fresh wind slabs on northeast slopes. Forecast snowfall amounts vary across the region. If you see more than 25 cm in your riding area bump the avalanche danger up to HIGH and expect to see storm slabs on all aspects. 

Confidence

Low - Forecast snowfall amounts are uncertain.

Weather Forecast

Monday Night: Snow 10-20 cm amounts vary across the region. Ridgetop wind strong from the southwest and alpine temperatures near -10. Freezing levels valley bottom.

Tuesday: Snow 5-10 cm with some sunny periods. Ridgetop wind strong from the South and alpine temperatures near -6. Freezing levels 900 m. 

Wednesday: Snow 5-10 cm. Ridgetop wind mostly light but gusty from the southwest. Alpine temperatures near -4 and freezing levels 900 m.

Thursday: Cloudy with some flurries. Ridgetop wind strong from the southwest. Alpine temperatures near -1 and freezing levels 1100 m. 

Avalanche Summary

No new reports on Monday.

On Sunday, a few natural wind slab avalanches were reported up to size 2 at treeline and in the alpine on northeast and northwest aspects. Wind slabs were also easily triggered on leeward slopes by the weight of a skier. Numerous loose wet avalanches were observed from steep terrain features. 

On Saturday, we received some fantastic MIN reports showing significant wind effect and wind loading at upper elevations. Natural avalanches were reported as well as a skier-triggered slab size 1.5. 

Thank you for the MIN reports!!

Reactive wind and storm slabs are the primary concerns for the forecast period. Loose-dry sluffing will likely be seen from steep terrain features. 

Snowpack Summary

Up to 25 cm of recent snow fell by Monday morning. Fresh winds slabs may be reactive on leeward slopes, while touchy storm slabs may be found in isolated wind-sheltered locations. This brings 50 to 80 cm of snow 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 old 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 heavy loading from new snow and wind.
  • Stick to simple terrain features and be certain your location isn't threatened by overhead hazard.
  • 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.

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.