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Avalanche Forecast

Archived

Jan 27th, 2018–Jan 28th, 2018

Alpine
Natural and human triggered avalanches likely.
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 unlikely, human triggered possible.

Regions

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Deteriorating weather conditions will increase the avalanche danger Sunday. Avalanches initiating near and above treeline may travel into tracks and runouts at lower elevations. Avoid large terrain where avalanches may run and stop at all elevations. Rain below treeline will change the character of avalanche conditions. Expect and avoid loose wet avalanches on steeper slopes at lower elevations.

Detailed Forecast

Warming temperatures, steady precipitation, and strong ridgetop winds will create increasing avalanche danger throughout Sunday. Natural avalanches are expected above treeline where dense new snow will load on top of soft snow from Friday and Saturday.

Wind slabs will build near and above treeline. Avalanches resulting in this terrain may step-down into older snow layers, entrain additional snow, become larger, and travel farther than you may expect. Avoid avalanche tracks and runouts. Avalanches may initiate at elevations above where you are traveling and run to your location.

Warming air temperatures and rain will create wet avalanche conditions at lower elevations. Expect wet surface snow to produce loose wet avalanche on steep slopes. Avoid slopes greater than 35 degrees below treeline as rain begins to fall on this cold dry snowpack.

Snowpack Discussion

Windy and snowy conditions Saturday continued across the east slopes of the Cascades adding an additional 4-6 inches of snow. This active weather pattern has deposited 24 inches of settled snow in northern areas and 8-10 inches of settled snow in souther areas over the 1/16 crust.

While several weak layers can be found within the storm snow, observations demonstrate most of these layers gaining strength.

Winds throughout the storm cycle have redistributed snow forming sensitive wind slabs on a variety of aspects. Winds have been strongest in the Central Cascades, especially Mission Ridge.

Observations from around the east slopes central and north found buried surface hoar above the 1/16 crust. There is still quite a bit of uncertainty around the distribution of this layer. Extra caution should be taken when traveling in areas further east  of the crest or in areas where less snow has been received. Snow profiles and snowpack test are the only means to identify and locate this layer. 

Snow depth still decreases substantially east of the Cascade crest. In many areas below treeline, there has not been enough snow to produce avalanche danger.

Observations

North

On Friday, North Cascades Mountain Guides found the upper snowpack generally gaining strength. Some snowpack test failed below the 1/16 crust.

On Thursday and Friday, NCH observed evidence of several recent wind slabs that had released in steep terrain above treeline in the Washington Pass area. Away from wind affected terrain and in several snowpits, a generally stable and right-side-up upper snowpack was noted. 

NWAC received a second-hand report of a large skier-triggered avalanche on west-facing slope (likely near treeline) on Abernathy Peak in the upper Twisp River drainage. The avalanche propagated widely and was suspected to have failed on the 1/16 crust.

Central

Mission Ridge Ski Patrol reported high winds and active wind loading on N-NE slopes Saturday. In wind sheltered location soft surface snow was found. Surface hoar has been observed in the area on the 1/16 crust.

A public observation from Wednesday in the Blewett Pass area identified basal facets at the bottom of the snowpack and surface hoar above the most recent crust. Snow cover was still regionally low in this area.

Buried surface hoar was found in the Icicle Creek drainage over the 1/16 crust over a week ago up to 6800 ft. 

South

No recent observations

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.

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.