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Avalanche Forecast

Archived

Dec 17th, 2025–Dec 18th, 2025

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

Regions

Coquihalla, Harrison-Fraser, Manning, Skagit.

60 to 100 cm of new snow over two days is a rapid load, and enough to bring a LOT of avalanche terrain online. Stick to simple or non-avalanche terrain that defends you from overhead hazards.

Confidence

Moderate

  • Forecast snowfall amounts are uncertain.

Avalanche Summary

No new avalanches reported, but it's a safe bet that a natural cycle took place at the height of the Tues/Wed storm as up to 60 cm piled up. Below treeline areas are likely approaching or even above threshold.

Expect more active conditions with the next storm.

Last Wednesday, a size 3 stepped down to a deep weak layer near Allison Pass. It's a lone data point from before the atmospheric river, but leaves some questions about a possible lingering deep problem in high alpine.

Snowpack Summary

30 to 45 cm of new snow should fall Wednesday night through Thursday, with the greatest amounts expected on the Coquihalla. Allison Pass may get missed.

The new snow will add to 35 to 60 cm from the Tuesday/Wednesday storm, which covers a crust forming on the rain-soaked snowpack below.

An older crust with facets, formed in mid-November, should now be about 80 to 150 cm deep in the alpine. The rain ought to have cleaned out this problem where it existed, but with few recent observations and loading ongoing, thin-to-thick snowpack areas in the high alpine remain a bit suspect.

Snowpack heights should reach about 140 to 200 cm by end of day Thursday. There's still not much snow below 1500 m.

Weather Summary

Wednesday Night
Cloudy with increasing snowfall bringing 10 to 15 cm of new snow. 50 km/h southwest ridgetop wind. Treeline temperature -4 °C. Freezing level reaching 1100 m.

Thursday
Cloudy with increasing snowfall bringing 20 to 30 cm of new snow, easing overnight. 40 km/h south ridgetop wind jumping to 60 km/h near end of day. Treeline temperature reaching 0 °C when the freezing level jumps to 1600 m near end of day.

Friday
Cloudy with continuing snowfall bringing 25 to 35 cm of new snow, including overnight amounts. 40 to 60 km/h southwest ridgetop wind. Treeline temperature -5 °C. Freezing level 1000 m.

Saturday
Mostly cloudy with easing snowfall bringing 30 to 40 cm of new snow, including overnight amounts. 60 km/h southwest ridgetop wind. Treeline temperature -6 °C. Freezing level 1000 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Use increased caution at all elevations. Storm snow is forming touchy slabs.
  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Don't let storm day fever lure you into consequential terrain.
  • Be especially cautious as you transition into wind-affected terrain.

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.