Avalanche Forecast

Issued: Feb 26th, 2019 3:28PM

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.

Watch for winds slabs in open terrain and around ridge features. Deeper and more reactive deposits will be in lee and cross-loaded terrain.

Summary

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

TUESDAY NIGHT: Clear with cloudy periods. Alpine temperatures near -18C. Ridgetop winds 20-25 km/h from the east.WEDNESDAY: Sunny with cloudy periods. Alpine temperatures near -15C. Ridgetop winds 15-25 km/h east.THURSDAY: Mostly cloudy with scattered flurries, trace to 6 cm snow. Alpine temperatures near -10C. Ridgetop winds around 15 km/h from the east.FRIDAY: Mainly cloudy with scattered flurries, 5 cm snow. Alpine temperatures near -18C. Ridgetop winds 25-30 km/h from the east.

Avalanche Summary

On Monday, small and thin (size 1) natural wind slab avalanches were reported on west to south-south east aspects. Similar small, thin slabs were reactive to skiers on north to east-southeast aspects at treeline and above. Additionally, a 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 burying faceted surface snow and a patchy layer of surface hoar. Between 1600-1800 m, another weak layer of surface hoar crystals buried around Valentines Day, is now 50-80 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 100-120 cm down and is most prominent between 1600-1900 m.The remainder of the snowpack is well-settled.

Problems

Wind Slabs

Outflow winds have produced wind slabs on various aspects and cross-loaded terrain. Look for signs of instability as you gain elevation and transition into wind-affected terrain.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

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.

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

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Feb 27th, 2019 2:00PM