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Avalanche Forecast

Archived

Feb 12th, 2019–Feb 13th, 2019

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

Regions

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 Heavy snow and wind created dangerous conditions, with reports of widespread avalanches. While the storm is winding down, it will still be easy to trigger large avalanches on Wednesday. Continue to use extra caution around steep slopes and put plenty of space between where you travel and large pieces of terrain where avalanches could start or run to from overhead slopes.

Discussion

Snow and Avalanche Discussion:

Widespread natural and triggered avalanches have been reported from the mountains throughout the zone, including from low lying terrain in Tumwater canyon and slopes outside of the city of Wenatchee.

Prior to the storm cycle that started on February 8, the very cold temperatures turned a layer of low density snow into facets. These facets rest over a mostly supportable crust, and are fairly widespread. These facets over a crust have been documented across the region, and we have reached critical load for this layer to wake up in a more widespread fashion. As the fluffy snow has piled up and the winds blow, it is becoming more and more cohesive. The size of the potential avalanches has increased, and once the slab can communicate a fracture across the terrain, watch out.

Facets are angular snow grains that bond poorly to other grains around it. Once formed, buried, and preserved, they tend to persist in the snowpack. They are often the culprit of deep and destructive avalanches that result in accidents. 

Snowpack Discussion

Regional Synopsis coming soon

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.