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Avalanche Forecast

Archived

Mar 18th, 2022–Mar 19th, 2022

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 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

North Columbia.

Buried weak layers continue to be reactive. Avalanches are likely where recent storm snow sits over a sun crust or surface hoar layer. 

Stick to conservative terrain and watch for signs of instability.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

FRIDAY NIGHT: Scattered flurries continue with mostly cloudy skies, around 5 cm expected. Moderate southwesterly winds. Freezing levels drop to 800 m.

SATURDAY: Scattered flurries with mostly cloudy skies, 5 cm possible over the day. Moderate southwesterly winds. Freezing levels rise to 1600 m. Alpine high of +1.

SUNDAY: 5-10 cm possible overnight. A mix of sun and cloud with light westerly winds. Freezing levels around 1300 m, alpine high of -3. 

MONDAY: Light snowfall with light southwest winds. Freezing levels rise to 1500 m. 

Avalanche Summary

On Thursday, numerous reports noted whumpfing and settlements in the weak layers. Large, naturally triggered storm slabs were observed on south facing slopes where the storm snow sits over a crust. A cornice fall also triggered a size 1.5 avalanche on the buried surface hoar layer on a north facing slope. This interface is still reactive to human triggers, with remotely triggered avalanches reported. Explosive control work produced size 2.5-3 slab avalanches, with impressive propagation on south facing slopes. 

Loose wet avalanches have been reported at elevations below the freezing line. 

On Wednesday, avalanche activity was reported to size 2.5. Avalanches were naturally and human triggered, mainly occurring on the buried weak layers below the storm snow. Activity mainly occurred on south and east facing slopes around treeline,

Snowpack Summary

Up to 60 cm of recent settling storm snow sits over a layer of weak surface hoar in sheltered and shaded terrain, and over a crust on south facing slopes. Test results show that the new snow is bonding poorly to old surfaces in many areas, producing large avalanches within the last 3 days. 

At higher elevations consistent southwest winds are creating deeper deposits on north through east facing features. Below 1500 m, moist snow or a melt-freeze crust likely exists from recent rain and warm temperatures.

The late February persistent weak layer combination of crust, facets and surface hoar is down 70-90 cm. Two persistent weak layers from mid-February and late January are buried 100-170cm deep. Avalanches on these layers are unlikely to be triggered.

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • 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.