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Avalanche Forecast

Archived

Feb 17th, 2023–Feb 18th, 2023

Alpine
Natural avalanches possible, human triggered probable.
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 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 avalanches possible, human triggered probable.

Regions

Coquihalla, Harrison-Fraser, Manning, Skagit.

Avalanches are likely to be triggered by light loads such as skiers in wind-loaded areas at all elevations. Carefully evaluate wind loading as you move through terrain and investigate the bond of wind slabs to the crust below them before committing to an open slope.

Confidence

Moderate

Avalanche Summary

On Thursday, A large (size 2.5) avalanche was observed during a helicopter observation flight. This naturally trigger slab avalanche was approximately 80 to 100 cm deep. It initiated at the ridgetop, 2000 m elevation, and ran 250m in length. This very steep and rocky terrain feature was on a northeast aspect and it is suspected that the avalanche ran on a crust formed mid-January. Noted large (size 2) glide slab activity was confined to steep south aspect rock faces between 1600 and 1800 m elevation.

On Tuesday, clear weather allowed operators to see into higher elevations. Evidence of a widespread avalanche cycle from last weekend's storm was observed throughout the region. Several natural cornice and windslab avalanches were observed to size 2.5. Several loose dry avalanches were observed to size 2 out of steep rocky features. These avalanches were all likely caused by past wind loading, warming, or solar input.

Please continue to post your reports and photos to the Mountain Information Network.

Snowpack Summary

Southwest winds continue redistributing 20 to 35 cm of available snow into lee features at higher elevations. On steep solar surfaces, you will find a thin melt-freeze crust. In sheltered areas, 20 to 30 cm of recent storm snow remains unconsolidated, this overlies an additional 50 cm of past HST that has settled and is well bonded.

A melt-freeze crust formed in mid-January is now buried up to 80-120 cm deep. At the moment this layer appears to be gaining strength though in isolated areas small facets are still found above the crust. The snow below this layer is consolidating nicely. Buried 120-150 cm is a crust, formed near the end of December.

Snowpack depths are just below seasonal averages. Total amounts range from 150 to 300 cm at treeline, but decrease significantly below 1500 m.

Weather Summary

Friday Night

Cloudy with light to moderate snowfall, 5 to 15 cm of accumulation. Winds southwest 30 km/h gusting to 50 km/h. Treeline temperatures -6 °C and freezing levels of 500 m. 

Saturday

Overcast with continued light to moderate snowfall, 5 to 10 cm of accumulation. Winds northwest 30 km/h gusting 50 km/h. Treeline temperatures -3 °C and freezing levels 1000 m.

Sunday

 Cloudy with very light isolated flurries, 1 to 5 cm of accumulation. Winds northwest 20 km/h gusting to 60 km/h. Treeline temperatures -3 °C and freezing levels of 1000 m. 

Monday

Cloudy with moderate to heavy snowfall, 10 to 25 cm accumulation. Winds northwest 50 km/h gusting 80 km/h. Treeline temperature -2 °C. Freezing level 1200 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 freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Seek out wind sheltered terrain below treeline where you can avoid wind slabs and find great riding.
  • Avoid areas with a thin or variable snowpack.

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.