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Avalanche Forecast

Archived

Feb 10th, 2019–Feb 11th, 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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Dangerous avalanche conditions continue to develop. The pre-existing snowpack was an ugly setup for all this new snow, and very deep slabs have formed. Be very cautious of steep, open slopes, as slides may be triggered from a distance. 

Discussion

Snow and Avalanche Discussion

We likely didn't have High danger in the near treeline band on Sunday. A widespread weak layer consisting of facets over a crust has been documented across the region, and things appeared to be materializing for this layer to wake up, but it hasn't....yet.

As the deep, fluffy snow becomes more cohesive above this layer and the storm snow continues to pile up, the size of the potential avalanches are increasing. Once the slab does begin to communicate a fracture across the terrain, watch out. This is a fairly unusual situation for the Cascades, and one to be taken very seriously as the cold temperatures, wind, and snowfall continue into the week.

Deep snow in sagebrush country has created a fairly unusual situation. We just doubled the amount of avalanche terrain in the area, and one in close proximity to Wenatchee. These slopes are steep, open, snow covered, and they have already produced avalanches. Numerous loose dry avalanches were observed in the steep foothills of Mission Ridge from Saturdays wallop. Tell your friends and family to be safe out there, whether it be in the mountains or the foothills, and hold them to it. This forecast may be updated at 0630 on Monday based on overnight storm totals. 

Most avalanche accidents occur with Considerable Danger. Be aware of your surroundings and ask yourself, "Am I in avalanche terrain? Could the snow slide?" Traveling one at a time is good practice, but remember, it does not eliminate the hazard of choosing to enter avalanche terrain. You can stay safe out there by choosing to avoid slopes steeper than 30 degrees, and places well away from steep open slopes. 

Image courtesy of Bruce Tremper.

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.