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Avalanche Forecast

Archived

Mar 28th, 2015–Mar 29th, 2015

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

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A mix of winter and spring avalanche conditions is likely west of the crest mainly above treeline on Sunday.

Detailed Forecast

Southwest flow on the west side of an upper ridge will continue to carry frontal moisture mainly to BC through Sunday. Expect some occasional light showers in the Olympics and northwest Cascades with fairer conditions east of the crest and further south with moderate temperatures.

It is spring and despite the moderate temperatures the sun will have more effect on the snow pack. The main avalanche problem should be loose wet avalanches. Watch for possible wet surface snow deeper than a few inches, increasing snow balling or natural loose wet avalanches. While this problem should be mainly on solar slopes watch for it on all steep slopes.

Wind slab may linger on lee slopes mainly above tree line. Watch for possible firmer previously wind transported snow mainly on north to east aspects.

Cornices won't be listed as an avalanche problem. But avoid slopes below cornices and ridges or summits where cornices may be hard to see.

Snowpack problems west of the crest for the time being should be in the upper or surface layers. The mid and lower  snowpack  west of the crest consists of layers of stable consolidated rounded grains or melt forms and crusts from multiple warm periods this winter. 

Less recent snow and ample terrain anchors may limit the avalanche danger below treeline. Many areas at the lowest elevations do not have enough snow to cause an avalanche danger.

Snowpack Discussion

Winter made a bit of a comeback in the Northwest in mid to late March. Several storms or storm cycles brought heavy snow to the above treeline areas west of the crest especially on the volcanoes. This caused slab avalanches and loose wet and loose dry avalanches at times with a couple involvements including in the closed Crystal Mountain Ski Area on March 24th - see the report via NWAC Observations.

A warm front caused pretty heavy rain mainly west of the crest Wednesday to Thursday morning. This caused an avalanche cycle and consolidation west of the crest with the most avalanches at Mt Rainier.

Large natural slab crown from March 25th in Wilson Chute on Mt Rainier, an east aspect at about 7000 feet. The crown extended over 1 km along the ridge. Photo taken March 26th by Dallas Glass.

Slab avalanches in the Tatoosh Range from March 25th. Photo taken March 26th Andrew Carey.

Very warm weather Thursday and Friday mainly caused more consolidation.

A vigorous front and short wave crossed the Northwest Friday night causing strong west-southwest winds, some rain and snow and lowering snow levels. Snow levels lowered enough by Saturday to cause up to 2-3 inches of snowfall at higher NWAC stations west of the crest and likely a few more inches at higher elevations.

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.