Avalanche Forecast
Issued: Feb 2nd, 2018 10:00AM
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
Ridge top winds will transport snow forming soft new Wind Slabs on lee slopes. Identify and avoid areas of wind deposited snow near and above treeline. Loose Wet avalanches will be possible in locations receiving rain. Stay off of steep slopes where small Loose Wet avalanches may have large consequences.
Summary
Detailed Forecast
Mild, showery, windy weather will maintain avalanche conditions into Saturday.
Moderate to strong winds will form fresh Wind Slabs on a variety of aspects. Visual clues will help you identify and avoid slopes where winds are depositing snow. Fresh cornices, snow drifts, plumes, and blowing snow all indicate where Wind Slabs are forming. Assessing Wind Slabs can be very difficult. Give this avalanche problem a wide berth until they have time to heal.
In locations receiving rain, wet surface snow conditions will lead to Loose Wet avalanches. You will be able to trigger Loose Wet avalanches on steeper slopes during and immediately following rain events. Avoid slopes where small avalanches may have large consequences such as above cliffs, rocks, creeks, and gullies.
Cornices have grown very large during recent stormy weather. Be aware of cornices overhead. Predicting when and where cornices will fail is extremely difficult. Use extra caution if traveling in areas where cornices exist on ridgelines above.
Avalanche hazard will be lower in areas receiving less precipitation further east of the crest.
Snowpack Discussion
Warming air temperatures and showery weather began to change surface snow conditions on the East Slopes of the Cascades Friday. Water amounts varied by location, but in most locations south of Holden rain has fallen up to 6000 feet.
Above 6000’ winds have formed fresh shallow wind slabs up to 6” thick.
A natural avalanche cycle has been reported in many areas from Monday’s warm wet weather. Rain occurred along the east slopes as far north as Holden, WA.
Scattered observations from the last week of January found buried surface hoar on top of the 1/16 crust. This persistent weak layer was found or thought to be the cause of several avalanches. Extra caution should be taken when traveling in areas further east of the crest where this layer may survive. Snow profiles and snowpack tests are the only means to identify and locate this layer.
Observations
North
A guide from NCH Friday reported new and reactive Wind Slabs developing due to strong ridge-top winds. Slabs were observed to be 4 inches thick.
Tuesday, reports from NCMG in the Cuttthroat drainage of Washington Pass indicated a natural avalanche cycle from Jan 29th. Many of these avalanches were large (D2-D2.5) and some were triggered by cornices falling onto the slope.
Central
An avalanche professional traveling in Icicle Creek Thursday found 6-8” of settled snow well bonded to the 1/29 crust. Observations demonstrated a strong upper snowpack. No buried surface hoar was found in this location.
On Tuesday, Mission Ridge Pro Patrol identified several layers of concern in this regionally shallower snowpack. These layers should be watched during future loading events. Similar basal weak layers were found in the nearby shallow snowpack of Blewett Pass.
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: Feb 3rd, 2018 10:00AM
