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Avalanche Forecast

Archived

Feb 17th, 2019–Feb 18th, 2019

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

Regions

Lizard-Flathead.

Recent observations of persistent slab avalanches indicate buried weak layers are touchy, particularly in openings like cutblocks and gullies. Also use caution at higher elevations, where the wind has likely turned recent soft snow into slabs.

Confidence

High -

Weather Forecast

SUNDAY NIGHT: Clear skies, light to moderate northeast wind, alpine temperature -21 C.MONDAY: Clear skies, light to moderate northeast wind, alpine temperature -18 C.TUESDAY: Increasing clouds over the day with light afternoon snowfall, trace accumulation, light to moderate west wind, alpine temperature -15 C.WEDNESDAY: Cloudy with light snowfall, accumulation 5 cm, light to moderate northeast wind, alpine temperature -13 C.

Avalanche Summary

On Sunday, a skier triggered a large (size 2 to 2.5) avalanche within a slide path on a northeast aspect near Fernie. The avalanche was about 40 to 80 cm deep, on a northeast aspect, and at 1700 m. Although speculative, it is suspected that the avalanche may have released on one or both of the weak layers described in the Snowpack Summary.On Saturday, widespread large (size 2) persistent slab avalanches were observed in the region - check the report out here and another one here. The avalanches released on the surface hoar described in the Snowpack Summary. The slabs were 40 to 100 cm deep. They released between 1550 m and 1700 m on north aspects. There was also further evidence of instability within the buried weak layers, as noted here and here.Otherwise, small to large (size 1 to 2) wind and storm slab avalanches were triggered naturally and by skiers in treeline and alpine terrain.

Snowpack Summary

Around 15 cm of recent snow overlies a weak layer of surface hoar crystals found between 1600 m and 1800 m. Strong wind may have redistributed this recent snow and formed wind slabs in lee terrain features at higher elevations. The wind was first westerly and switched to northeast, so wind slabs may be found on all aspects.Two weak layers may be found within the snowpack. Surface hoar that was buried early-February may be found about 40 to 50 cm deep in shaded and sheltered areas above 1600 m. The mid-January layer of surface hoar is buried around 80 cm and is most prominent between 1600 m and 1900 m.The remainder of the snowpack is well-settled. Thin snowpack areas, such as in the far east of the region, may have weak and sugary faceted grains near the base of the snowpack.

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.