Avalanche Forecast

Archived

Apr 21st, 2023–Apr 22nd, 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 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.

Forecast 15-25 cm of snow and extreme southerly wind will form reactive storm slabs.

Use small low consequence slopes to test the bond of the new snow and watch for signs of instability like whumpfing, hollow sounds, shooting cracks, or recent avalanches.

Confidence

Low

Avalanche Summary

A few naturally triggered size 2 wind slab avalanches were reported on steep, northerly aspects in the alpine on Thursday.

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

Forecast 15-25 cm of snow and extreme southerly wind will form reactive storm slabs.

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.

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

Weather Summary

Friday Night

Cloudy with flurries; 3-15 cm / 60 km/h south ridgetop wind / Temperature at treeline around -3 C / Freezing level 900 m

Saturday

Snow; 10-20 cm, then another 10-20 cm overnight / 70 km/h south ridgetop wind / Temperature at treeline around -2 C / Freezing level 1200 m

Sunday

Cloudy with flurries; 5-10 cm / 40 km/h south ridgetop wind / Temperature at treeline around -3 C / Freezing level 1100 m

Monday

Cloudy with flurries; 5-10 cm / 50 km/h southwest ridgetop wind / Temperature at treeline around -4 C / Freezing level 1000 m

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Storm slab size and sensitivity to triggering will likely increase through the day.
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.
Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.

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.