Avalanche Forecast

Archived

Feb 13th, 2016–Feb 14th, 2016

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

Olympics.

The continued warming trend Sunday and additional rain or snow will increase the likelihood of natural or triggered avalanches. Dangerous avalanche conditions are expected Sunday.

Detailed Forecast

Increasing moderate to heavy rain and snow is expected with a warming trend Saturday night through Sunday. With the snow level expected to rise to near 6000 feet by early Sunday, a significant increase in avalanche danger is expected overnight with natural avalanches becoming likely.

Continued rain and snow Sunday at further rising freezing levels should maintain dangerous avalanche conditions. Many slopes may have released naturally overnight Saturday, locally lowering the danger on those slopes, however on slopes that have not released due to warming and additional load, natural or triggered avalanches should be increasingly likely Sunday.

Snowpack Discussion

Weather and Snowpack

A large upper ridge and warm air mass aloft over the West Coast from this past Sunday through Wednesday led to the warmest weather of the winter. During this stretch temperatures were generally well above freezing. After some light rain Thursday afternoon and night, rain changed to light snow showers with sunbreaks by late Friday morning at Hurricane Ridge. Additional cool snow showers Friday night through Saturday afternoon have combined to deposit about 6 inches of storm snow as of Saturday afternoon.

Professional NWAC observer, Matt Schonwald was at Hurricane Ridge on Friday. Recent warmth and persistent winds have generally created a dense and homogeneous snowpack without any layers of concern. In the Hurricane Ridge area the snowdepth falls off rapidly below 4400 feet. Bare patches or thin snow cover is widespread along ridgelines and south through west aspects. Matt and an NPS ranger did observe 2 glide avalanches that likely occurred Thursday night. The larger one, size D2, released in the June 20th path down to a gravel bed. However, except in isolated terrain features, glide avalanches should not be a widespread concern in the Hurricane Ridge area.

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.

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 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.