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Avalanche Forecast

Archived

Apr 20th, 2023–Apr 21st, 2023

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, 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

Kitimat, Seven Sisters, Howson.

Triggering large persistent slab avalanches on weak facets in the alpine is currently the primary concern.

Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.

Confidence

Low

Avalanche Summary

No avalanches were reported on Wednesday. However, observations in this region are currently very limited.

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 in isolated locations in the alpine. A crust exists up to ridgetop on south-facing slopes and on all aspects up to approximately 1300 m.

A weak layer buried in late March is down 40-60 cm and exists as surface hoar and facets on north-facing slopes and a crust elsewhere.

At treeline elevations, a melt-freeze crust exists on all aspects.

The mid and lower snowpack is considered generally strong and well-bonded.

Weather Summary

Thursday Night

Partly cloudy / 10 km/h northwest ridgetop wind / Temperature at treeline around -4 C / Freezing level 800 m

Friday

Mix of sun and cloud / 20 km/h southwest ridgetop wind / Temperature at treeline around -2 C / Freezing level 1400 m

Saturday

Snow; 5-15 cm / 60 km/h south ridgetop wind / Temperature at treeline around -3 C / Freezing level 1300 m

Sunday

Cloudy with flurries; 5-10 cm / 30 km/h south ridgetop wind / Temperature at treeline around -4 C / Freezing level 1200 m

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • Wind slabs may be poorly bonded to the underlying crust.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

Problems

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.

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.