Avalanche Forecast
Issued: Mar 3rd, 2015 10:00AM
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
It is getting to be the time of year when you often need to watch for both winter and spring types of avalanche conditions. It is always good to read the forecast for details.
Summary
Detailed Forecast
Light winds and sunny weather with warmer temperatures should be seen on Wednesday.
The sun will be out and stronger and the days are getting longer. It is hard to say how much of a problem loose wet avalanches might be on Wednesday. Watch for wet snow deeper than a few inches or rollerballs or pinwheels on steep solar slopes. The problem of loose wet avalanches should not be extensive but limit your terrain choices if you see more activity than expected.
Wind transported snow from last Friday and Saturday is most likely to linger on unusual south to northwest facing slopes on Wednesday. But on most slopes the sunny weather will have caused these layers to bond with underlying layers and it should no longer be a problem.
Cornices will not be listed as a problem yet but start to practice checking the ridges for these as we shift into spring.
Due to the low snowpack, especially below treeline, watch for terrain hazards such as open creeks, partially covered rocks and vegetation. Many areas below treeline do not have enough snow (new or existing) to pose an avalanche hazard.
Snowpack Discussion
The North Cascades Mountain Guides in the Washington Pass area reported a well bonded dense snowpack on February 22nd. No results from tests and rounding grains were seen at the January 15th facet/crust layers.
NWAC pro-observer Tom Curtis was in the north end of the Chiwakums on February 25th and found minor new snow on a hard thick crust, no avalanche problems and a low avalanche danger in all the elevation bands.
The latest snowfall was Wednesday to Friday when up to about 7 inches of snow fell east of the crest.
This was followed by local strong northeast winds in the Cascades Friday and Saturday. This is expected to have caused the most transport near treeline onto lee west slopes.
Minor cooler weather on Sunday and Monday has been followed by sunny weather on Tuesday. East winds remained pretty weak Monday night. This weather will have caused consolidation and stabilizing.
The persistent weak January 15th facet/crust layers can still be identified in parts of the NE Cascades but have been stabilizing and have become unlikely to trigger. As a result the Persistent Slab problem has been removed from the northeast zone.
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: South, South West, West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Mar 4th, 2015 10:00AM
