Avalanche Forecast

Issued: Feb 20th, 2019 4:21PM

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

jcoulter, Avalanche Canada

Lizard-Flathead.

Observations of persistent slab avalanches indicate buried weak layers are touchy, most recently below 1800 m. In the alpine, expect wind slabs on a variety of aspects.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

TONIGHT: Cloudy with flurries 3-5 cm, light to moderate north east winds, alpine temperature -17 C.THURSDAY: Cloudy with sunny breaks, winds switching from north east to southwest mid-day, alpine temperatures -11 C.FRIDAY: Cloudy with light precipitation, accumulation 5 cm, moderate south west winds, alpine temperature -8 C.SATURDAY: Cloudy with light precipitation, winds out of the east, alpine temperatures -8 C.

Avalanche Summary

Skier triggered small to large (size 1-2) wind slabs have been reported on various aspects in open areas over the past few days. Most recently a skier remote triggered a large wind slab at treeline on a south west aspect on Tuesday. On Tuesday, whumpfing in previously un-compacted (not tracked up when the weak layers formed) terrain was reported. Whumpfing in the sound a weak layer makes when it collapses from the weight of a slab above it in mellow terrain. If it were in steeper terrain, it would likely cause an avalanche. On the long weekend, many persistent slab avalanches were observed. A skier triggered a large (size 2 to 2.5) avalanche within a slide path near Fernie. The avalanche was about 40 to 80 cm deep, on a northeast aspect, and at 1700 m. The South Rockies Field Team attended the site on Tuesday and confirmed that the avalanche failed on a layer of surface hoar, check out their report here. Also on Sunday a group of skiers remote triggered a size 2 avalanche (no involvement) over a convexity in the Little Sand area at 1650 m. Cutblock type terrain in the Rolling Hills has also been the source of persistent slab observations check the report out here .

Snowpack Summary

Storm snow from last week has been redistributed by wind, forming wind slabs in open areas at higher elevations. The wind was first westerly and switched to northeast, so wind slabs may be found on all aspects. In sheltered areas between 1600 and 1800 m, 20 cm of recent snow may sit on a weak layer of surface hoar crystals buried around Valentines Day in some locations.Two more persistent weak layers may be found within the snowpack. Surface hoar that was buried early-February may be found about 30 to 50 cm deep in shaded and sheltered areas above 1600 m. The mid-January layer of surface hoar is buried around 70 to 100 cm and is most prominent between 1600 m and 1900 m.

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.

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

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible - Likely

Expected Size

1.5 - 3

Wind Slabs

Wind was first from the west and shifted to the northeast, which likely moved the recent snow around at higher elevations. Use particular caution near ridges or open areas where the snow feels stiff.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Feb 21st, 2019 2:00PM