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Avalanche Forecast

Archived

Mar 13th, 2015–Mar 14th, 2015

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.

Regions

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Quite a change in the weather is expected on Saturday. You should mainly need to watch for loose wet snow avalanches but read the forecast discussion for details.

Detailed Forecast

A front that taps sub tropical moisture should cause strong southwest winds and increasing moderate to heavy rain in the Cascades on Saturday. It looks like an initial wave on the front will somewhat evenly affect the Cascades from Mt Baker to Mt Hood.

The moderate to heavy rain is expected to reach above treeline in the Cascades on Saturday. On any slopes holding old powder or less consolidated surface snow this will likely cause loose wet avalanches. Watch for wet surface snow deeper than a few inches, natural avalanches, and pinwheels or rollerballs on steep north facing or previously shaded slopes mainly above and perhaps near treeline.

Below treeline rain is not expected to have as much effect since the Cascade snowpack on these slopes beforehand is so limited, consolidated and stable. 

It seems possible that any cornices will get a bit of a test Saturday. Although cornices are not as big as usual this year give ridges with cornices and slopes below cornices a safety margin.

Some snow may also be seen in the upper above treeline in the Cascades on Saturday. This won't be listed as a problem since it only seems possible in the upper above treeline and loose wet snow should be the predominate problem. But watch for new storm slab in areas that accumulate more than a few inches of new snow during the day if you venture into the upper above treeline of the Cascades.

Quite a change in the weather is expected on Saturday so watch for any signs that conditions are turning out different than expected.

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 to cause an avalanche danger.

Snowpack Discussion

The latest warm dry period of the winter was seen from the start of March through Tuesday. In the Cascades this caused more consolidation and stabilizing. Reports indicated thickening surface crusts on most slopes and some corn snow development on solar slopes. Lingering varied more winter-like surface conditions were still seen on some north slopes at higher elevations.

A weak front crossed the Northwest Wednesday to Thursday morning. NWAC sites west of the crest picked up anywhere from about .1 to 1.6 inches of rain with the least at Crystal and the most on the volcanoes especially Mt Baker. There may have been up to a few inches of new snow on the volcanoes above treeline especially at Mt Baker.

There have not been any reports of significant avalanches in the Cascades for many days. There was nearly no snowfall January to so far in March near and below treeline. The snowpack at low elevations remains meager to non-existent. 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.

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.

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.