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Avalanche Forecast

Archived

Mar 2nd, 2021–Mar 3rd, 2021

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

Regions

Northwest Coastal.

More snow and a strong southwest wind continues to build touchy storm slabs. Its a good time to sit out the storm and avoid avalanche terrain. Storm slabs have the potential to step-down to deeper persistent weak layers, triggering large avalanches. 

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Tuesday Night: Snow 5-10 cm. Ridgetop wind light from the South. Freezing levels in the valley bottom.

Wednesday: Snow 15-25 cm. Ridgetop wind moderate from the southwest. Alpine temperatures -2 and freezing levels 700 m.

Thursday: Mixed rain and snow, snow 10-20 cm. Ridgetop wind light from the southeast. Alpine temperatures near 0 and freezing levels 1100 m. 

Friday: A mix of sun and cloud. Ridgetop wind from the South. Alpine temperatures near -5 and freezing levels valley bottom. 

Avalanche Summary

On Tuesday, explosive control up to size 2 was reported in the recent storm snow. 

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

60-80 cm of recent storm snow blanketed the region over the past few days. This was accompanied by strong to extreme southwest winds building deeper wind slabs on leeward slopes. Below 1000 m new snow is landing on a crust that formed during last weekend's storm. Massive cornices exist on ridgelines at treeline and in the alpine. 

Snowfall accumulation now brings 90-250 cm over the plethora of old snow surfaces buried mid-February and deeper down buried late January. These old persistent weak layers comprise of hard wind-packed snow, feathery surface hoar crystals especially in areas sheltered from the wind, and sugary faceted snow that developed during the cold snap. 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

  • Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • 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.
  • The more the snow feels like a slurpy, the more likely loose wet avalanches will become.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.