Avalanche Forecast

Archived

Apr 2nd, 2017–Apr 3rd, 2017

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

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Avoid steep sun exposed terrain if you see wet snow deeper than a few inches and initial rollerballs or small loose wet avalanches that can indicate an increasing loose wet avalanche danger. Avoid travel on or below cornices. Wind slab may still be present near ridges above treeline in the Northeast zone.

Detailed Forecast

Light winds and sunny weather should be seen on Monday with moderately warmer temperatures.

Sunshine will melt and possibly cause loose wet snow avalanches on steep solar slopes. Avoid steep sun exposed terrain if you see wet snow deeper than a few inches and initial rollerballs or small loose wet avalanches that can indicate an increasing loose wet avalanche danger.

Past wind slabs should have mostly stabilized where formed on lee slopes, mainly above treeline and on NW-SE aspects, but will remain listed as an avalanche problem in the Northeast zone for higher terrain that received heavy storm snow Wednesday.

Recent cornices are very large. Natural cornice releases and resulting slab avalanches are dangerous and unpredictable. Give cornices a wide berth if traveling along ridge-lines and avoid slopes below large cornices. See a blog post regarding cornices here.

Snowpack Discussion

Weather and Snowpack

March was wet and wild for weather and avalanches in the Cascades.

The last major system in March was seen Tuesday and Wednesday. Another 5-10 inches fell near the Cascade crest along with a warming trend and increasing W-SW alpine winds. Lesser amounts were seen further east of the crest and at lower elevations.

Cooling and showery weather Thursday allowed wet snow to begin refreezing with light amounts of new snow in most areas. The winds diminished Thursday and combined with daytime warming, this has allowed for wind slab and storm slab to begin stabilizing.

Very mild temperatures and increased solar radiation Friday allowed for wet surface snow conditions in most terrain, even northerly facing slopes.

A weak front crossed the Northwest on Saturday morning causing light rain mainly along the Cascade west slopes. This was followed by an upper trough on that caused some light amounts of snow along the Cascade west slopes at much cooler temperatures on Sunday. In most areas this will have refrozen upper layers of the snowpack.

Recent Observations

North

The NCMG were in the Cutthroat area on Monday 3/26 and found 15-20 cm of recent snow on a firm base. Loose wet avalanches and cornices were the main concerns.

On Tuesday 2/27, the NCMG in the Highway 20 Hairpin area found that ski and hand tests indicated good bonds of recent snow to previous snow. Loose wet avalanches were the main concern at lower elevations. Touchy or stubborn wind and storm slab, and cornices were still expected near and above treeline.

A public observation from the Washington Pass area on Tuesday 3/27 reported small ski triggered 10 in wind or storm slab on steep E slopes near a ridge line.

Central

No recent observations.

South

No recent observations.

Problems

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.

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.