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Avalanche Forecast

Archived

Apr 20th, 2023–Apr 21st, 2023

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

Regions

Northwest Inland, Kispiox, Microwave-Sinclair, Ningunsaw, South Bulkley, South Bulkley, Telkwa.

Fresh wind slabs may be reactive to human triggers on lee aspects in the alpine.

Avoid steep, rocky, and wind affected areas where triggering slabs are more likely.

Confidence

Low

Avalanche Summary

A naturally triggered size 2 wind slab was reported on a northeasterly aspect in the alpine on Thursday. See MIN.

Observations are limited at this time of year, please consider sharing any information or photos you have on the Mountain Information Network to help guide our forecasts.

Snowpack Summary

10-20 cm of recent snow and strong southeast wind formed wind slabs that may remain reactive to human triggers on lee aspects at treeline and above. A crust exists up to ridgetop on south-facing slopes and on all aspects up to approximately 1500 m.

A weak layer buried in late March is down 30-50 cm and exists as surface hoar and facets on north-facing slopes and a crust elsewhere. Test results show that this layer may be reactive to human triggers in isolated locations on north-facing slopes where the layer is well-preserved and have a cohesive overlying slab.

The middle of the snowpack is strong and contains numerous hard crusts. Near the ground, weak faceted crystals exist. There hasn't been avalanche activity on this layer recently, but it remains on our radar and may become active when we experience change, such as rapid loading (heavy snowfall or rain) or prolonged warming.

Weather Summary

Thursday Night

Mostly cloudy with isolated flurries; 3-15 cm / 30 km/h east ridgetop wind / Temperature at treeline around -4 C / Freezing level 600 m

Friday

Mix of sun and cloud with isolated flurries; 0-10 cm / 20 km/h southeast ridgetop wind / Temperature at treeline around -2 C / Freezing level 1500 m

Saturday

Cloudy with flurries; 5-10 cm / 30 km/h south ridgetop wind / Temperature at treeline around -3 C / Freezing level 1300 m

Sunday

Cloudy with isolated flurries; 0-10 cm / 20 km/h southeast ridgetop wind / Temperature at treeline around -1 C / Freezing level 1600 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.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.

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.