Avalanche Forecast

Archived

Apr 6th, 2013–Apr 7th, 2013

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

South Coast.

Confidence

Fair - Track of incoming weather is uncertain on Sunday

Weather Forecast

Synopsis: A low pressure system is forecast to move through Washington on Sunday, most likely giving cloud and only light precipitation to the South Coast. If it tracks a little further north we could see greater accumulation. A ridge of high pressure should build in later on Sunday resulting in drier conditions and sunny breaks for Monday and Tuesday. Sunday: Mainly cloudy with a chance of flurries. The freezing level is around 1000-1200 m. Winds are easing to light from the northeast. Monday: Sunny breaks. The daytime freezing level rises to around 1500 m. Winds are light from the northwest. Tuesday: Increasing cloud and the possibility of snow late in the day. The freezing level is steady around 1500 m.

Avalanche Summary

Observations are very limited. Continued loose wet activity is likely at lower elevations from recent rain, and the possibility of triggering new wind slabs exists in higher terrain.

Snowpack Summary

Recent snowfall amounts vary depending on location and elevation. Some alpine areas (above 1800-1900 m) could have accumulations of over 30 cm. New dense wind slabs are likely in exposed lee and cross-loaded terrain in the alpine. Most of the recent precipitation has fallen as rain at and below treeline. The upper snowpack at lower elevations has become isothermal from recent warm temperatures. Loose wet sluffs remain a concern below treeline. Cornices are very large and could pop off with continued mild temperatures.

Problems

Wind Slabs

Wind Slab avalanches are the 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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

Loose Wet

Loose Wet avalanches are the 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. 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.