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Avalanche Forecast

Archived

Apr 2nd, 2018–Apr 3rd, 2018

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

Regions

Lizard-Flathead.

Recent storm snow may remain reactive on wind-loaded terrain features and where it sits above crusts.

Confidence

Moderate - The weather pattern is stable

Weather Forecast

TUESDAY: Mix of sun and cloud with some light flurries (accumulations of 1-3 cm), moderate west wind, alpine high temperatures near -6 C, freezing level up to 1200 m.WEDNESDAY: Increasing cloud, light to moderate southwest wind, alpine high temperatures near -4 C, freezing level up to 1400 m.THURSDAY: Light flurries with 5-10 cm of snow, moderate southwest wind, alpine high temperatures near -8 C, freezing level at valley bottom.

Avalanche Summary

On Monday, natural avalanches up to size 2 were reported in alpine terrain while skiers and explosives triggered several size 1 avalanches at lower elevations. The 20 cm of new snow was poorly bonding to the crust and produced slab avalanches in wind-affected terrain and loose dry avalanches elsewhere.On Sunday, small loose dry avalanches (size 1) were reported in steep terrain and one size 2 wind slab avalanche was triggered with explosives on a north aspect at 2100 m.On Saturday, a large slab avalanche was triggered in the west of the region. See this MIN post for a photo and more details. A small wind slab avalanche at treeline was also reported.

Snowpack Summary

15-25 cm of snow on Sunday night has fallen above a melt-freeze crust on sunny aspects and all aspects below 1700 m. The new snow has been wind-affected and may take awhile to bond to the crusts.A surface hoar and crust layer buried mid-March is found around treeline at a depth of about 80 cm, with weak surface hoar on northerly aspects and the crust elsewhere. Deeper in the snowpack, the late-November weak layer is composed of sugary facets around a crust, which is buried around 200 to 300 cm deep and is currently dormant.Cornices are large along ridgetops and were actively failing last week.

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.