Avalanche Forecast
Issued: Mar 7th, 2016 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
You will need to watch for new layers in some areas and for a combination of winter and spring conditions if you venture out on Tuesday.
Summary
Detailed Forecast
A weakening front should move over a flat ridge and over the Northwest Tuesday afternoon and night. Snow from this front should mainly reach the Olympics, the southwest Cascades and at Mt Hood by the end of the daylight hours on Tuesday.
New snow may be enough to form new wind and storm slab layers mainly in the above tree line zones in the Olympics, the southwest Cascades and at Mt Hood by the end of the daylight hours on Tuesday. A rule of thumb is that storm slab is likely when snowfall accumulates at more than an inch an hour for several hours.
Older or previous wind slab may also still be present near and above treeline along the west slopes. Watch for firmer wind transported snow.
Loose wet avalanche conditions may still be possible mainly on solar slopes below tree line along the west slopes. Watch for wet snow deeper than a few inches, pinwheels and natural loose wet avalanches.
Snowpack Discussion
Weather and Snowpack
Last week was wet and relatively mild with a series of active fronts transiting the region resulting in fluctuating freezing levels and periods of very strong winds. The heaviest snowfall and precipitation occurred late Sunday 2/28 and Tuesday 3/1. The latter half of the week and the weekend featured more rain than snow at NWAC sites along the west slopes.
Mid and lower elevations late last week and over the weekend saw natural and triggered loose-wet avalanches most days due to increasing solar effects or during rain events.
Particularly in the Mt. Baker area, unsupported slabs continue to sporadically release during extended stretches of mild temperatures and rainfall resulting in glide avalanches in very specific terrain features like steep rock faces.
The mid and lower snow pack along the west slopes should generally be a stable mix of crusts and layers of moist and rounded snow crystals.
Recent Observations
NWAC pro-observer Tom Curtis was at Stevens Pass on Friday found evidence of lots of large loose wet and some wet slab avalanches.
A private report to the NWAC indicated loose wet avalanches on Friday near Alpental as well.
Locally heavy rain at the Mt. Baker area led to sensitive loose wet ski cuts by the Mt. Baker pro-patrol Saturday morning. A natural loose wet cycle was observed in the Bagley Lakes area and one glide avalanche in unsupported terrain released nearby. Also in the Baker area, a glide avalanche occurred Saturday night off Shuskan Arm entraining moist surface snow and becoming very large while running to the valley bottom.
A report on Turns All Year for the Crystal area for Saturday indicated wet snow conditions with pinwheels on north and south slopes.
A report via the NWAC Observations page for Sunday for Snoqualmie Pass also indicated wet heavy snow conditions and previous loose wet avalanches.
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: North, North East, East, South East.
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: Below Treeline.
Likelihood
Expected Size
Valid until: Mar 8th, 2016 10:00AM
