Avalanche Forecast
Issued: Mar 23rd, 2015 11:50PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Loose Wet and Wind Slabs.
NWAC,
Northwest Avalanche Center
The cool somewhat snowy weather should bring a variety of changeable March snow and avalanche conditions.
Summary
Detailed Forecast
Light snow showers may be seen at higher elevations east of the crest on Tuesday with fairly low snow levels.
The cool somewhat snowy weather may bring a variety of changeable March snow and avalanche conditions.
We are past the equinox and the sun is rapidly getting stronger and new snow will be susceptible to sun effects. Watch for possible wet snow deeper than a few inches or snowballing or natural loose wet avalanches by Tuesday midday on solar slopes.
Possible small wind slab may linger on lee slopes mainly ATL. Use extra caution near slope convexities where storm or wind slab avalanches are more likely to be triggered.
Less recent snow and ample terrain anchors should limit the avalanche danger below treeline. Many areas below treeline do not have enough snow to cause an avalanche danger.
Snowpack Discussion
The 15-18 inches of snow that fell a week ago mainly in the north Cascades including east of the crest has settled or melted by at least 10 inches and probably been absorbed into the upper snowpack.
Daily warming should have made the upper snowpack mostly homogeneous in most east slope areas.
The storm late last week and over the weekend only deposited light amounts of new snow to most of the east slopes.
The DOT crew working at Washington Pass on Monday stable overall snow conditions and no avalanches with 4-6 inches of recent snow above the pass and about 2 inches at pass level.
Snowdepths vary greatly across the east slopes with a regionally healthy snowpack in the northeast Cascades to bare solar and lower elevation slopes for the central and southeast Cascades.
A weak upper short wave and unstable air mass is moving over the Northwest on Monday. Some light snow showers should make it east of the crest. Another rapidly moving shortwave will carry a surface low across the north Oregon Cascades Monday night. This should renew snow showers Monday night in the south Cascades with possible overnight stormy conditions at Mt Hood.
Problems
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.
Aspects: South East, South, South West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
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, North West.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Mar 24th, 2015 11:50PM
