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Avalanche Forecast

Archived

Mar 24th, 2015–Mar 25th, 2015

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Olympics.

A big dose of warm front moisture will arrive in the Olympics and Cascades on Wednesday. This should cause an increase in the avalanche danger on Wednesday in the Olympics mainly above treeline where there is significant snow.

Detailed Forecast

A big dose of warm front moisture will arrive in the Olympics and Cascades on Wednesday. Rain or snow should be heaviest in the Olympics and central to south Cascades Wednesday morning and shift to the north Cascades Wednesday afternoon and evening. Snow levels will be a moving target but the sure thing is they will be going up pretty rapidly on Wednesday. The main avalanche danger increase should be above treeline on the higher peaks of the Olympics.

The warming trend and initial snow will help build new upside down new storm slab where there is at least a few hours of snowfall of an inch or more an hour. In the Olympics this should be likely above treeline on Wednesday morning.

The warming trend and initial snow will also help build new wind slab on lee slopes. In the Olympics this should also be likely above treeline on Wednesday morning.

A change to rain should generally be seen in the Olympics on Wednesday. This is likely to begin to cause a cycle of loose wet avalanches on many slopes above treeline Wednesday afternoon.

Most areas below treeline in the Olympics do not have enough snow to cause an avalanche danger.

Snowpack Discussion

The 16-18 inches of storm snow that fell March 14th-15th mostly melted at Hurricane Ridge. The total snow depth at the NWAC weather station settled or melted and lost 10 inches last week.

Just a few inches of new snow accumulated last weekend. Winds may have built some small cornices along ridges and built some small wind slabs on lee slopes.

A fairly vigorous low pressure system moved east over the Mt Hood area last night to this morning. The main snowfall was in the south Cascades with only about 3 inches at Hurricane.

Overall the snowpack remains meager at Hurricane. There is probably only enough recent snow for avalanches above treeline on the higher peaks of the Olympics.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

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.

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.