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Avalanche Forecast

Archived

Feb 27th, 2021–Feb 28th, 2021

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 and human triggered avalanches likely.
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 Coastal.

Warm, wet and windy! 

A widespread natural avalanche cycle is likely on Sunday. Its a good time to stay out of avalanche terrain and avoid overhead slopes. Large to very large avalanches could run full path into lower elevations. 

Confidence

High - We are confident the likelihood of avalanche will increase with the arrival of the forecast weather. Forecast precipitation (either snow or rain) amounts are uncertain.

Weather Forecast

WET, WARM, and WINDY!

Saturday Night: Snow amounts 15-25 cm. Ridgetop wind strong from the southwest and alpine temperatures near -2. Freezing levels 600 m.

Sunday: Heavy snow 25-40 cm accompanied by strong wind from the southwest. Alpine temperatures near 0 and freezing levels 1000 m.

Monday: Cloudy with light snow 5-10 cm. Ridgetop wind moderate to strong from the southwest. Freezing levels 500 m.

Tuesday: Snow amounts 10-20 cm. Ridgetop wind moderate to strong from the southwest. Alpine temperatures near -3 and freezing levels 600 m. 

Avalanche Summary

No new avalanches reported on Saturday. 

On Friday, numerous avalanches up to size 3 were triggered with the use of explosives. Many being size 1-2 storm slabs, however; one reported was a size 3 with the suspect failure plane being the mid-February facet interface described in the snowpack summary. A widespread natural avalanche cycle occurred on Thursday and overnight into Friday up to size 3. Additionally, This MIN from earlier this week shows excellent photos of slab avalanches around treeline elevations, potentially releasing on the surface hoar. 

I expect a widespread avalanche cycle on Sunday.

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

Snowpack Summary

Storm after storm, after storm! 

30-60 cm of new storm snow fell by Friday morning. This came with strong southwest to northwest wind building fresh wind slabs and storm slabs at upper elevations. Below 800 m mixed precipitation of snow and rain likely fell leaving moist snow surfaces on a snowpack that was recently wet. 

This now brings 80-200 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

  • Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
  • Avoid the runout zones of avalanche paths. Avalanches could run full path.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Keep in mind that wet avalanches can be destructive due to their high density.
  • Keep in mind that human triggering potential persists as natural avalanching tapers off.

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.