Avalanche Forecast

Archived

Feb 9th, 2019–Feb 10th, 2019

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 possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

.

A unique and strong storm clipped the area and may have created wind slabs in unusual locations. Be cautious of recent wind loaded slopes from the foothills to the mountaintops. In outlying regions south and east of Mazama, lingering persistent weak layers may be possible to initiate on Sunday.

Discussion

Snow and Avalanche Discussion

The powerful storm produced lots of new snow and wind in the adjacent East Central and Southeast Zones. On Saturday, avalanche professionals found nearly a foot of new snow on Delancy Ridge. Much of this snow lacked cohesion, or a slab structure. Areas of wind slab are more likely to have formed closer to Washington Pass, where winds funneled through and sped up.

The following may apply more to outlying areas such as south and east of Mazama to north of Lake Chelan, where more new snow may have fallen: Most avalanche accidents occur with Considerable Danger. Avalanches may be possible in unusual places like steep sagebrush foothills. 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. Slopes of less than 30 degrees, and places well away from steep open slopes would be my preferred terrain choice for Sunday.

Image courtesy of Bruce Tremper.

Snowpack Discussion

Coming soon.

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.