Avalanche Forecast

Issued: Feb 18th, 2018 4:02PM

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

mconlan, Avalanche Canada

Lizard-Flathead.

Recent snow and strong winds have produced touchy wind slabs. Watch for signs of avalanche activity and locally unstable snow, such as whumpfing and shooting cracks.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

MONDAY: Partly cloudy, light northeasterly winds, alpine temperature -15 C, freezing level below valley bottom.TUESDAY: Mostly sunny, light westerly winds, alpine temperature near -12 C, freezing level below valley bottom.WEDNESDAY: Mostly sunny, moderate westerly winds, alpine temperature near -11 C, freezing level below valley bottom.

Avalanche Summary

Naturally triggered storm slabs were noted up to size 2.5 between 1800 and 2100 m on Sunday.Â They were 20 to 40 cm deep and on northerly to easterly aspects.Â One of the avalanches was likely triggered by a cornice fall during Saturday's storm.On Saturday, Many small to large (size 1 to 2) storm slabs and cornices were triggered by explosive control at treeline and alpine elevations. The storm slabs were about 20 cm deep on north to northeast aspects.

Snowpack Summary

Around 50-80 cm of recent snow has created storm slabs. The snow fell with strong variable winds, creating wind slabs in direct lee features on all aspects. This overlies a surface hoar layer and a melt-freeze crust buried mid-February up to 1800 m, and old wind slabs and a sun crust at higher elevations.Deeper in the snowpack, a widespread weak layer from mid-December composed of facets, crusts, and surface hoar is 120-160 cm deep. Also, a rain crust with sugary facets buried in late November is near the base of the snowpack. There has been regular avalanche activity on these layers over the past month. If triggered, they could produce large, destructive avalanches with high consequences.

Problems

Wind Slabs

Recent storm snow fell with strong winds that have produced touchy wind slabs in lee features on all aspects. These slabs will likely be reactive to natural and human triggers. Be cautious of overhead exposure on solar aspects when the sun is out.

If triggered, the wind slabs may step down to deeper layers, resulting in large avalanches.Choose shallow-angled and sheltered terrain where new snow hasn't been wind-affected.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2.5

Cornices

Cornices have grown in size with the recent storms and have been reactive to explosives. If released, they could produce large avalanches that run far.

Avoid travelling below large corniced ridges.Remain well back from corniced ridges, giving them a wide berth.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3.5

Deep Persistent Slabs

Several weak layers are lurking in our snowpack. If triggered, they could propagate far, producing avalanches with high consequences. Watch out for thin spots in the snowpack, where it is more likely to trigger them.

Be aware of the potential for wide propagation.Avalanches could run full-path: avoid runout zones of avalanche paths.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Valid until: Feb 19th, 2018 2:00PM