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Avalanche Forecast

Archived

Mar 15th, 2019–Mar 16th, 2019

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

Regions

Lizard-Flathead.

We're expecting mostly cloudy conditions on Saturday, but slopes receiving direct sun could produce loose wet avalanches surprisingly quick.

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

FRIDAY NIGHT: Mainly cloudy, alpine low temperature -5C, light southwest wind.SATURDAY: Cloudy with sunny periods, alpine high temperature of -2C, light west wind at most elevations, moderate at ridgetop, freezing level around 2000m. SUNDAY: Sunny with cloudy periods, alpine high temperature of 0C, light west wind. freezing level around 2200m, no overnight re-freeze expected.MONDAY: Mix of sun and cloud, alpine high temperature of +3C, light west wind at ridgetop, freezing level around 2500m, no overnight re-freeze expected.

Avalanche Summary

On Thursday, a group of riders remotely triggered a size 1.5 persistent slab after seeing many shooting cracks and whumpfs. See the MIN report for more details. Several loose wet avalanches (size 1-1.5) were also triggered by riders on steep south facing slopes at treeline. A bit of natural activity, mainly loose avalanches, were observed on steep slopes. With this upcoming warming, natural avalanches are increasingly likely as the sun impacts solar aspects.

Snowpack Summary

The snow surface is getting moist on south and west slopes at lower elevations. Up to 40 cm of storm snow in the last week overlies various surfaces such as old and firm wind slabs in the alpine and open areas at treeline on all aspects. A widespread sun/ temperature crust is also found hidden under this new snow on south facing slopes. Isolated pockets of surface hoar crystals were observed at the surface on north-facing slopes around 2000m right before the last storm rolled in. The mid-snowpack consists of sugary faceted grains (facets) of different hardness. Two older layers of surface hoar still exist down 55-80 and down 95-150 around 1600-1900m. The lower snowpack is generally 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.