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Avalanche Forecast

Archived

Mar 14th, 2019–Mar 15th, 2019

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

Regions

Lizard-Flathead.

Storm slabs are the main concern, but it may be possible to trigger deeper weak layers with this upcoming warming.

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

THURSDAY NIGHT: Cloud. Slight chance of flurries. Alpine temperatures low of -5C. Moderate north-west winds at ridgetops. FRIDAY: Isolated flurries in morning. Mix of sun and clouds. Alpine temperatures high of -2C. Light to moderate west winds.SATURDAY: Sunny with cloudy periods. Alpine temperatures high of -2C. Light to moderate west winds. Freezing level around 1600m to 1800m. SUNDAY: Sunny with cloudy periods. Alpine temperature high of +2C. Light to moderate west winds. Freezing level between 2000m and 2300m.

Avalanche Summary

On Thursday, a group of sledders remotely triggered a size 1.5 persistent slab after seeing many shooting crack and whumpfs. See the MIN report for more details. Wednesday, numerous storm slabs avalanches (size 1-2) were triggered by skiers on northerly aspects near ridgetops. Few larger loose dry avalanches (size 2-2.5) were also triggered by explosives on steep alpine slopes. Thursday, the sun has initiated several loose wet avalanches on solar aspects at treeline and above.

Snowpack Summary

Moist snow on the surface of sunny slopes. Up to 40 cm of recent storm snow 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 this 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.