Avalanche Forecast

Issued: Feb 27th, 2019 3:30PM

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

dsaly, Avalanche Canada

Lizard-Flathead.

Recently formed wind slabs and wind-affected snow may quickly be hidden under a thin cover of flurries falling through Thursday. Expect a more reactive snowpack in areas where winds pick up and 10 cm snowfall accumulates.

Summary

Confidence

Moderate -

Weather Forecast

WEDNESDAY NIGHT: Clear with cloudy periods. Alpine temperatures near -10C. Ridgetop winds 10-20 km/h from the east.THURSDAY: Cloudy with scattered flurries, 5-10 cm snow. Alpine temperatures near -9C. Ridgetop winds 15-30 km/h south-southeast.FRIDAY: Mainly cloudy with scattered flurries, 5 cm snow. Alpine temperatures near -18C. Ridgetop winds 25-30 km/h from the east.SATURDAY: Sunny. Alpine temperatures near -20C. Ridgetop winds 15-20 km/h from the east-northeast.

Avalanche Summary

Cracking and other signs of instabilities have been reported around ridgetops, check out this MIN report from Tuesday here.On Monday, small (size 1) natural wind slab avalanches were reported on west to south-south east aspects and reactive to skiers on north to east-southeast aspects at treeline and above. Additionally, machine operator on a road at 1700 m triggered a small (size 1) slab avalanche with a 40 cm crown which failed on on a layer of well preserved surface hoar between crusts.Last Saturday, numerous natural and explosives triggered storm slab avalanches to size 2-2.5 were reported. These were 50-100 cm deep running on east through north aspects in the alpine and treeline. Loose, dry snow is sloughing in steeper terrain. On Sunday, a skier triggered a size 1 storm slab avalanche on a north aspect around 2100 m.Last Thursday, before the weekend snowfall, an explosive triggered a large (size 2.5) persistent slab avalanche. The slab was about 40 cm deep and failed on a southerly aspect between 1650 and 2000 m.

Snowpack Summary

Winds are redistributing recent snowfall forming scouring ridgetops and producing wind slabs in open areas at treeline and above. The recent snow covered wind-affected surfaces in the alpine and treeline. In sheltered areas and lower elevations, the new snow is settling over facets and a patchy layer of surface hoar and a crust on solar aspects.Between 1600 and 1800 m, another weak layer of surface hoar crystals is now 30-50 cm below the snow surface. Two more weak layers of surface hoar may be found within the snowpack. One buried early-February, is 40-80 cm deep in shaded and sheltered areas above 1600 m. The other buried mid-January, is 80-110 cm down and is most prominent between 1600 m and 1900 m.The remainder of the snowpack is well-settled.

Problems

Wind Slabs

Around 10 cm snow is expected to accumulate by the end of day Thursday. Accompanied with moderate winds, flurries will hide recently formed wind slabs and potentially be redistributed into touchy deposits in wind-loaded areas.

Be careful with wind loaded pockets, especially near ridge crests and roll-overs.Keep an eye out for reverse loading created by variable winds.If triggered, storm or wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

Two weak layers of surface hoar may be found between 1500 m and 1900 m, around 60-120 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.

Watch for signs of instability such as whumpfing, cracking, or recent avalanches.Be aware of the potential for wide propagation.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 2.5

Valid until: Feb 28th, 2019 2:00PM