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Avalanche Forecast

Archived

Apr 22nd, 2023–Apr 23rd, 2023

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

Regions

Coquihalla, Harrison-Fraser, Manning, Skagit.

Consider starting with small slopes in simple terrain, and watch how the surface snow is changing through the day. A wet and dynamic storm could bring rapid change to the snowpack.

The biggest concerns are fresh storm slabs in the alpine, and rain soaking any dry snow that remains at treeline and below.

Confidence

Moderate

Avalanche Summary

On Saturday in the Coquihalla area, daytime warming caused numerous naturally triggered wet loose avalanches in steep terrain. The largest of these avalanches was a size 2.

Looking forward, similar wet loose avalanches could continue while it rains at and below treeline. Also, new snow and moderate southwest wind at treeline and above mean wind slabs could be triggered by riders in lee terrain features.

Use plenty of caution along alpine ridges, where cornices may be large.

Snowpack Summary

15 to 20 cm of new snow in the alpine and into upper treeline. Moderate southwest wind building fresh windslab on the existing windslab, or on a breakable crust on solar aspects.

Below treeline, a mix of rain and snow will be falling on a variety of moist or frozen surfaces.

The remainder of the snowpack is strong with varying hard snow layers and bonded melt-freeze crusts. Cornices are large along many alpine ridges.

Weather Summary

The rain/snow amounts below represent the west side of the forecast area. The forecasted precipitation amounts are much lower east of the Coquihalla summit and Allison Pass.

Saturday Night

Cloudy. Light to moderate snow/rain, 5 to 10 mm. Chance of freezing rain. Snow/rain line around 1400 m. Treeline low around 0°C. Light to moderate south or southwest ridgetop wind.

Sunday

Cloudy. Moderate snow/rain, 8-12 mm. Snow/rain line between 1250 and 1500 m. Treeline low around -1°C. Moderate southwest ridgetop wind.

Monday

Low cloud. Light snow/rain expected overnight and through the day, 5-15 mm. Snow/rain line rising from 1000 to 1500 m. Light west or southwest ridgetop wind.

Tuesday

Mostly sunny by the afternoon. Trace of snow/rain expected. Freezing level rising to between 1800 and 2200 m. Light west or southwest ridgetop wind.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Watch for unstable snow on specific terrain features, especially when the snow is moist or wet.
  • Use ridges or ribs to avoid areas of wind loaded snow.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

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.