Avalanche Forecast
Issued: Mar 28th, 2018 1:27PM
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 may trigger wind slab avalanches Thursday on wind loaded slopes especially near convex rollovers, steep unsupported slopes, and beneath cornices. Use visual clues such as wind textured snow, firm snow surfaces, and cornices to identify and avoid steep wind loaded slopes. If the sun comes out or the clouds thin, expect snow conditions to change quickly becoming wet and loose. If you see signs of new rollerballs, loose wet avalanches, or experience wet snow deeper than your ankle, stay off of nearby slopes greater than 35 degrees.
Summary
Detailed Forecast
You may still trigger lingering wind slab avalanches Thursday on wind loaded slopes and cross-loaded feature. You are most likely to trigger these avalanches on NW-NE aspects, steep convex rollovers, unsupported slopes, and below cornice. Use visual clues such as snow drifts, cornices, wind textured snow, and firm snow surface conditions that produce cracks to identify and avoid wind loaded areas.
If the sun comes out or the clouds thin, expect the strong March sun to quickly effect the surface snow. This can occur very quickly this time of year and does not take full bright sunshine to occur. If you see new rollerballs, observe new loose wet avalanches, or experience wet surface snow deeper than your ankle, it’s time to change slopes. Avoid slopes greater than 35 degrees on aspects where you see any of these pertinent observations.
Although not listed as an avalanche problem Thursday, you may still find lingering storm slabs in non-wind effected areas near treeline or in areas where more recent snow has fallen. Choose lower consequence travel routes to ease into terrain. If you experience cracking or sudden collapses in the snowpack, avoid nearby avalanche startzones.
Snowpack Discussion
Rain and snow showers Wednesday did not add significant accumulation to the recent storm totals. No new avalanches were reported.
Snow accumulation earlier this week depends on elevation. Snow levels fluctuated form near 6000 ft in the south to 5000 ft in the North. Above the recent rain line 12-18 inches (30-45cm) of snow fell Monday and Tuesday. Moderate winds during transported snow and formed wind slabs at higher elevations. Below the rain line, wet snow conditions formed. Observations indicate that much of this water is draining out of these lower elevation snowpacks.
In some location (especially near Crystal Mountain) an interface from 3/22 has been found to be reactive in snowpack tests. Small weak sugar facets have been reported just above a very firm and thick melt-freeze crust on E-S-W aspects. This layer has been observed 12-18 inches (30-45cm) below the snowsurface. Below this interface, the snowpack is generally well-rounded, strong, and lacking interfaces of concern.
An old, thin layer of sugary facets (2/13) can still be found in some locations just above a very firm and wide spread crust (2/8). The overall depth (5-6 feet, 1.5-2 meters) and significant rounding (melt-freeze cycles in some locations) has allowed this structure to drop off the official list of avalanche problems. NWAC professionals will continue to track this weak layer as it could be a problematic later in the spring.
Observations
North
On Wednesday Mt Baker Ski Patrol reported 8-12 inches (20-30cm) of soft snow over a recent melt-freeze crust. This snow was very rapidly effected by small sun breaks and thinning in the clouds. Winds earlier in the weak formed new wind slabs at higher elevations.
Central
On Tuesday, Stevens Pass Pro-Patrol reported gusty west winds redistributing snow onto all aspects. Rain at Pass level in the afternoon caused small Wet Loose avalanches. A skier triggered avalanche was reported outside the ski area near Gemini Pass. This slab avalanche may have released down to the 3/22 crust.
South
On Wednesday. NWAC professional observer Ian Nicholson traveled in the Crystal backcountry. Ian found a 1" (2-3cm) surface crust on all aspects in the morning. This crust quickly broke down on sun exposed slopes as clouds thinned mid-day. Ian did observe the 3/22 interface and found that it was still reactive in some snowpack tests. This layer was 12-18" (30-45cm) below the snow surface.
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: Mar 29th, 2018 1:27PM
