Avalanche Forecast
Issued: Jan 27th, 2018 10:59AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Loose Wet.
NWAC,
Northwest Avalanche Center
You will be able to trigger lingering wind slabs Sunday. Identify and avoid slopes where recent winds have deposited snow such as below cornices and on snow drifts. At lower elevations avoid terrain where small loose wet avalanche may create higher consequences such as above cliffs and creeks.
Summary
Detailed Forecast
Mild showery weather will allow avalanche hazard to decrease Sunday. You will be able to trigger lingering wind slabs on lee slopes near and above treeline. Identify and avoid areas of wind deposited snow such as below fresh cornices, on snow drifts, and on cross-loaded slopes.
Warm air temperatures and rain showers will develop moist surface snow at lower elevations. Watch for new roller balls on steep slopes. These are signs that loose wet surface conditions have developed. Avoid steeper slopes where loose avalanche can occur. Extra caution should be taken in areas of higher consequence such as above cliffs, gullies, and open creeks where small wet avalanches may carry you into these dangerous features.
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
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.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Loose Wet
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. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. 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.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Valid until: Jan 28th, 2018 10:59AM
