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Avalanche Forecast

Archived

Dec 29th, 2020–Dec 30th, 2020

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

Regions

Glacier.

We currently have a complex snowpack with persistent weak layers that could produce high consequence avalanches if you were unlucky enough to trigger them.

Be particularly cautious on open slopes with a crust at the Dec. 7th weak interface.

Weather Forecast

High pressure will give stable weather for one more day. A frontal system arriving from the Northwest will give increasing wind and steady snowfall Wednesday.

Today: Mix of sun and cloud. Alpine High -8 C. Ridge wind light SW.

Tonight: Cloudy with isolated flurries. Alpine Low -10 C.

Wednesday: Snow (15cm). High -8 C. Ridge wind moderate-strong SW.

Snowpack Summary

Up to 25cm of recent snowfall is being stiffened into a slab in some wind exposed areas. This new snow covers spotty surface hoar in sheltered areas at and below treeline. Weak layers persist down 70-110cm (Dec 13 surface hoar), and 110-130+cm (Dec 7 crust/facte/surface hoar).  The Nov. 5th crust complex is near the base of the snowpack.

Avalanche Summary

There were MIN reports of skiers triggering loose dry avalanches up to size 2 in steep terrain, and one small storm slab in an immediate lee at treeline.

There was a natural size 2.5 storm slab from steep North facing terrain on Mt Macdonald.

Several very large avalanches last week failed on the early December crust, facet/surface hoar combo.

Confidence

Intensity of incoming weather systems is uncertain

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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.

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.