Avalanche Forecast
Issued: Mar 2nd, 2015 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
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
A period of northeast ridge top winds and east pass winds should be seen in the Cascades this afternoon and tonight.
Then decreasing winds and sunny weather should be seen in the Cascades on Tuesday.
Watch for new shallow wind transported snow on unusual south to west facing slopes on Tuesday. Older wind slab from February 27th-28th is also most likely to linger on similar slopes.
The sun will be out and stronger and the days are getting longer so keep an eye on solar slopes for wet snow and signs of loose wet snow on solar slopes on Tuesday.
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 February 25-27th when up to about 7 inches of snow fell east of the crest.
This was followed by local strong northeast winds in the Cascades February 27-28th. This is expected to have caused the most transport near treeline onto lee west slopes.
A minor weak weather system yesterday and today did not cause significant precipitation or change in snow conditions.
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
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
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
Valid until: Mar 3rd, 2015 10:00AM
