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Avalanche Forecast

Archived

Apr 25th, 2023–Apr 26th, 2023

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

Regions

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

8:20 AM Update: Snow and wind have likely formed new storm slabs that could be reactive to riders. Conservative terrain travel is recommended.

Confidence

Moderate

Avalanche Summary

A size 2.5 cornice fall was reported on a northerly aspect in the alpine on Monday. Additionally, a naturally triggered size 2 wind slab was observed on a northeast aspect in the alpine.

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 storm slabs reactive to human triggers.

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

Tuesday Night

Snow; 15-30 cm / 60 km/h south ridgetop wind / Temperature at treeline around -3 C / Freezing level 1000 m

Wednesday

Snow ending mid-morning, then mostly cloudy; 10-15 cm / 50 km/h southwest ridgetop wind / Temperature at treeline around -3 C / Freezing level 1000 m

Thursday

Mix of sun and cloud / 40 km/h southwest ridgetop wind / Temperature at treeline around -1 C / Freezing level 1200 m

Friday

Sunny / 10 km/h west ridgetop wind / Temperature at treeline around 10 C / Freezing level rapidly rising to 3200 m!

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Only the most simple non-avalanche terrain free of overhead hazard is appropriate at this time.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Use small low consequence slopes to test the bond of the new snow.
  • Storm slabs in motion may step down to deeply buried weak layers resulting in very large avalanches.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.

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.