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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 unlikely, human triggered possible.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Northwest Coastal.

Snowfall amounts vary across the region. If you see more than 25 cm in your local area bump the danger to HIGH. Natural avalanche activity may taper off but skier and rider triggering is likely. Its a good time to have a conservative mindset and stick to simple terrain.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Monday Night: Snow 5-10 cm. Ridgetop wind strong from the southwest and alpine temperatures near -5. Freezing levels 300 m.

Tuesday: Snow 10-15 cm Ridgetop wind strong from the South and alpine temperatures near -3. Freezing levels 700 m. 

Wednesday: Snow 20-30 cm. Ridgetop wind mostly light but gusty from the southwest. Alpine temperatures near -4 and freezing levels 700 m.

Thursday: Snow 15-20 cm. Ridgetop wind strong from the southwest. Alpine temperatures near -1 and freezing levels 900 m. 

Avalanche Summary

Over the weekend a widespread natural avalanche cycle occurred up to size 3 and explosive control initiated numerous size 2-3 storm slabs and persistent slabs.

The storm continues and natural avalanche activity will likely occur through the forecast period. 

It's a good time to stay very conservative, stick to simple terrain, and be aware of overhead hazards like large avalanche paths and cornices. 

Snowpack Summary

40-60 cm of recent storm snow blanketed the region. This was accompanied by strong ton extreme southwest winds building deeper wind slabs on leeward slopes. Below 1000 m mixed precipitation of snow and rain likely fell leaving moist snow surfaces that are now refrozen.

This brings 90-250 cm over the plethora of old snow surfaces buried mid-February and deeper down buried late January. These lold layers comprise of hard wind-packed snow, feathery surface hoar crystals especially in areas sheltered from the wind, sugary faceted snow that developed during the cold snap, and a hard melt-freeze crust below treeline. These weak layers have been the result of several larger avalanches in the past week. 

The mid-pack has been reported as being well-settled. There are presently no deeper concerns.

Terrain and Travel

  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
  • Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.