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Avalanche Forecast

Archived

Jan 12th, 2019–Jan 13th, 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.

Regions

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The Bottom Line: We are in a low probability, but high consequence scenario for avalanches that could break into old snow layers. Upper elevations are the main concern for these, and for shallow, wind slabs that may build from light winds. Loose avalanches will become possible with strong sun and warming temperatures during the middle of the day.

Snow and Avalanche Discussion

Folks looking to get into the high mountains should realize that there is a fair amount of uncertainty with our snowpack above 6,000ft, with the warming, and there is a lot of variability within the zone. A common structure to be found out there will be storm snow (with or without a wind slab) over a crust from January 3rd. The storm snow from January 8/9 may not be bonding very well to the crust at upper elevations, where a thin layer of weaker snow has been found just above this crust. Recent wind slab avalanches ran on the crust at Mission Ridge and were from 6" to 16" deep and from 60' to 125' wide. One started on a Northwest aspect at 6300ft and broke through the crust into weak snow near the ground. At low elevations and on southerly aspects, a number of loose wet avalanches have been observed.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.