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Avalanche Forecast

Archived

Feb 23rd, 2025–Feb 24th, 2025

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

Regions

Coquihalla, Harrison-Fraser, Manning, Skagit.

New snow is bringing a critical load to buried persistent weak layers. The consequences of triggering an avalanche could be much higher than surface instabilities suggest.

Confidence

Moderate

Avalanche Summary

A natural size 3 persistent slab was observed in Allison Pass on Sunday, strong evidence of the persistent slab problem seen in adjacent regions emerging in the Cascades. It occurred on a 37°, northeast-facing slope at treeline (1740m) and had a 240 m-wide crown fracture. While it's clear it was a persistent slab, whether it failed on the late January crust or a more recent layer of faceted snow is uncertain. Storm loading is increasing concern for this type of activity.

Snowpack Summary

Around 20 cm of new snow and high southwest winds Sunday night will layer a fresh storm slab problem across the region and otherwise bring storm totals to about 50 - 60 cm overlying a weak layer of faceted snow or surface hoar existing in higher elevation, particularly shaded terrain.

Storm loading has woken this layer up decisively in neighbouring regions and it produced a troubling size 3 avalanche in Allison Pass on Saturday. High elevation rain bought moisture to the facet layer at treeline on Saturday, both a possible trigger and a suggestion that the layer may strengthen soon.

A crust from December is buried 80 - 140 cm deep, with facets around it in shallow areas. Otherwise, the lower snowpack is strong.

Weather Summary

Sunday Night

Cloudy with snow showers bringing about 20 cm of new snow, increasing with elevation, rain below about 1000 m. 20 to 30 km/h southwest ridgetop wind. Freezing level 1700 m.

Monday

Clearing over the day before clouding over again in the afternoon. 10 to 30 km/h southwest ridgetop wind. Freezing level 1300 m - 1700 m.

Tuesday

Cloudy with scattered wet flurries bringing less than 5 cm of new snow, including overnight. 10 - 30 km/h variable south ridgetop wind. Freezing level 1200 - 1600 m.

Wednesday

Becoming sunny. 10 - 30 km/h south ridgetop wind. Freezing level shooting to 2700+ m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Closely monitor how the new snow is bonding to the old surface.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Be aware of the potential for large avalanches due to buried weak layers.
  • Avoid thin areas like rocky outcrops where you're most likely to trigger avalanches on deep weak layers.

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.