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RegisterDec 29th, 2019–Dec 30th, 2019
Lizard-Flathead.
Triggering large avalanches is now a low probability/high consequence scenario that can be managed by careful terrain selection.
SUNDAY NIGHT: Clearing with some clouds, light wind from the northeast, alpine temperatures drop to -12 C.
MONDAY: Mix of sun and cloud, light wind from the northwest, alpine high temperatures around -7 C.
TUESDAY: Periods of snow starting midday with 5-15 cm by the evening, moderate wind from the southwest with strong gusts, alpine high temperatures around -5 C.
WEDNESDAY: Another 5-10 cm of snow overnight then isolated flurries in the afternoon, moderate wind from the southwest, alpine high temperatures around -3 C.
A few small (size 1) human triggered wind slab and dry loose avalanches have been reported since Christmas Day. A widespread cycle of very large deep persistent slab avalanches occurred a week ago (up to size 3.5). The likelihood of triggering a deep persistent slab avalanche has declined since then, but the consequences are severe. A MIN report from Friday north of Fernie (in the South Rockies forecast region) shows the possibility of triggering large avalanches from thin spots in rocky alpine terrain.
Sheltered terrain has 10-30 cm of soft snow while thin wind slabs have formed at higher elevations. The soft snow overlies a hard rain crust below 1700 m.
Hard snow in the middle of the snowpack sits above weak snow and crusts near the bottom of the snowpack (80-150 cm deep).This weak snowpack structure resulted in very large avalanches last weekend. The likelihood of triggering a deep persistent slab avalanche has declined since then, but could still be possible from thin spots in steep terrain that did not avalanche in the last storm. Another round of avalanche activity on these deep weak layers is possible when the next significant storm arrives.