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Avalanche Forecast

Archived

Apr 24th, 2023–Apr 25th, 2023

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 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.

Regions

Northwest Coastal, Kitimat, Nass, Rupert, Seven Sisters, Shames, Stewart, Howson, Ningunsaw.

Forecast snow and strong southwesterly wind are expected to form fresh wind slabs on lee features at treeline and above.

Concern for triggering large persistent slab avalanches remains. Avoid steep, rocky, and wind-affected areas where triggering slabs are more likely.

Confidence

Low

Avalanche Summary

Numerous avalanches were reported near Shames on Sunday, but poor visibility prevented detailed observations. See MIN.

Additionally, numerous naturally triggered wet loose avalanches up to size 2 were reported on all aspects/elevations.

A fatal avalanche occurred north of Stewart on April 11th. It was a skier-triggered size 3 persistent slab avalanche that occurred on a northeast aspect in the alpine.

Most professional operations are now closed which means we have very little snowpack or avalanche observation data. Please consider sharing any information or photos you have on the Mountain Information Network to help guide our forecasts.

Snowpack Summary

Forecast snow and strong southwesterly wind are expected to form fresh wind slabs on lee features at treeline and above.

A crust exists up to ridgetop on south-facing slopes and on all aspects up to approximately 1300 m.

The primary concern is two buried weak layers down 40-140 cm deep in most areas. They include facets and surface hoar in shaded areas and a melt-freeze crust elsewhere. Numerous human-triggered persistent slab avalanches have occurred on these layers during the past week.

The mid and lower snowpack is considered generally strong and well-bonded. In the far northern reaches of the region, basal facets may exist which are currently considered inactive. This layer may become active with abrupt changes to the snowpack, such as rapid loading (heavy snowfall or rain) or prolonged warming.

Weather Summary

Monday Night

Snow; 10-20 cm / 50 km/h southwest ridgetop wind / Temperature at treeline around -3 C / Freezing level 800 m

Tuesday

Mix of sun and cloud with isolated flurries; 0-5 cm, then another 15-30 cm overnight / 30 km/h southwest ridgetop wind / Temperature at treeline around -1 C / Freezing level 1100 m

Wednesday

Mix of sun and cloud with flurries; 5-10 cm / 60 km/h southwest ridgetop wind / Temperature at treeline around -1 C / Freezing level 1200 m

Thursday

Mostly cloudy / 40 km/h southwest ridgetop wind / Temperature at treeline around 2 C / Freezing level 1500 m

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.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.

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.

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.