Avalanche Forecast

Issued: Feb 17th, 2019 4:42PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Persistent Slabs and Wind Slabs.

mconlan, Avalanche Canada

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.

Summary

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

Two weak layers of surface hoar may be found between 1500 m and 1900 m, around 40 to 80 cm deep in the snowpack. These layers have been the culprit of recent large avalanches, particularly in openings such as cutblocks, gullies, and slide paths.

Be aware of the potential for wide propagation.Make observations and assess conditions continually as you travel.Watch for signs of instability such as whumpfing, cracking, or recent avalanches.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 3

Wind Slabs

The recent snow may continue to be reactive to human traffic. Wind was first from the west and shifted to the northeast, which likely moved the recent snow around at higher elevations. Use particular caution in lee terrain features near ridges.

Keep an eye out for reverse loading due to northeast wind.If triggered, wind slabs may step down to deeper layers resulting in large avalanches.Use caution in freshly wind-loaded features, especially near ridge crests and in steep terrain.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Valid until: Feb 18th, 2019 2:00PM