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Avalanche Forecast

Archived

Mar 12th, 2025–Mar 13th, 2025

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

Regions

Coquihalla, Manning, Skagit.

Storm slabs may be reactive to human triggering, especially at upper elevations.

Careful snowpack evaluation, cautious route-finding, and conservative decision-making are essential.

Confidence

Moderate

Avalanche Summary

On Tuesday, sluffing from the intermittent solar input occurred in steep terrain. Continued evidence of a widespread cycle to size 2 from last weekend's storm was reported. Some of the avalanches ran on the February persistent weak layer down 100 + cm.

Storm slabs may be reactive to human triggers on Wednesday, especially at treeline and in the alpine on leeward slopes that have seen more wind loaded snow.

Snowpack Summary

Up to 65 cm of storm snow sits above a crust on all aspects except on high, north-facing alpine terrain, where the new snow sits above an interface of dry snow. In some areas, beneath the new snow sits surface hoar on the crust. This crust/ surface hoar formed in early March. Moderate to strong southwest winds have redistributed storm snow into deeper pockets on lee slopes at the ridgeline.

A persistent layer of facets and surface hoar which formed in February have been found 80 to 140 cm down, and a layer of facets and surface hoar from late January can be found down to 120 to 180 cm. Recent snowpack testing shows a sudden planar result on surface hoar down 145 cm.

Weather Summary

Wednesday Night

Cloudy with 5 to 10 cm. 10 to 45 km/h southwest ridgetop wind. Treeline temperature -1 °C. Freezing level 1000 m.

Thursday

Cloudy with snow 10 to 20 cm. HIgher amounts possible for Allison Pass area. 15 to 40 km/h southeast ridgetop wind. Treeline temperature -4 °C. Freezing level 1000 m.

Friday

Cloudy with sunny periods. 10 to 15 km/h southeast ridgetop wind. Treeline temperature -2 °C. Freezing level 1200 m.

Saturday

Cloudy with 3 to 7 cm of snow. 15 to 55 km/h southwest ridgetop wind. Treeline temperature -2 °C. Freezing level 1200 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Watch for fresh storm slabs building throughout the day.
  • Avoid lee and cross-loaded slopes in the alpine.
  • Keep your guard up as storm slabs may remain sensitive to human triggering.
  • 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.