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Avalanche Forecast

Archived

Feb 22nd, 2019–Feb 23rd, 2019

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Lizard-Flathead.

Snowfall observations were far exceeding forecast amounts on Friday afternoon in the Fernie area. Treat the danger as CONSIDERABLE if you encounter 25 cm of new snow or more on Saturday.

Confidence

Low - Forecast snowfall amounts are uncertain

Weather Forecast

Friday night: Cloudy with flurries bringing 5-10 cm of  new snow, with a possibility of enhanced low density amounts of 20 cm or more. Light to moderate southwest winds.Saturday: Mainly cloudy with easing isolated flurries and a trace of new snow. Light to moderate northeast winds. Alpine high temperatures around -15.Sunday: Sunny with cloudy periods. Light northeast winds. Alpine high temperatures around -20.Monday: Cloudy with sunny periods. Light to moderate northeast winds increasing over the day. Alpine high temperatures around -17.

Avalanche Summary

An explosive triggered a large (size 2.5) persistent slab avalanche on Thursday. It was on a southerly aspect and between 1650 and 2000 m. The slab was about 40 cm deep.Last 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 remotely triggered a size 2 avalanche in the Little Sand area at 1650 m, as seen here. Cutblock-type terrain in the Rolling Hills has also been the source of persistent slab avalanches, see here.

Snowpack Summary

Light new snow amounts have buried mainly wind affected surfaces at alpine and treeline elevations, with snowfall forecast to continue through Friday night. In sheltered areas, the new snow is burying faceted surface snow and in some areas a new layer of surface hoar. Wind slabs exist in open, exposed areas at higher elevations. They may be found on all aspects due to variable wind directions. 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 weak layers of surface hoar 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.The remainder of the snowpack is well-settled.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.