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Avalanche Forecast

Archived

Mar 24th, 2015–Mar 25th, 2015

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

Regions

Mt Hood.

A big dose of warm front moisture will arrive in the Olympics and Cascades on Wednesday. This should cause a big increase in the avalanche danger on Wednesday including at Mt Hood.

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 and avalanche danger levels will be a moving targets but the sure thing is they will be going up pretty rapidly on Wednesday. There should be a bit less snow and rain at Mt Hood compared to the Olympics and Washington Cascades. Snow should change to rain soonest at Mt Hood.

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. At Mt Hood this is possible mainly above treeline through the morning.

The warming trend and initial snow will also help build new wind slab on lee slopes. At Mt Hood this is also mainly possible above treeline through the morning.

A change to rain should be seen to above treeline at Mt Hood about late morning. This is likely to begin to cause a cycle of loose wet avalanches on many slopes in all elevation bands.

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

Snowpack Discussion

About 4-6 inches of snow was seen above about 6000 feet Saturday as reported by the Meadows ski patrol. The winds and new snow did build some stiff wind slab on northeast slopes up to 1 foot in places. But these stiff slabs were unreactive to ski cutting as the new snow fell on old wet snow and formed a good bond and thus were resistant to triggers.

No additional avalanche activity was reported Sunday by Meadows patrol.

A fairly vigorous low pressure system moved east over the Mt Hood area last night to this morning and temporary winter-like conditions returned to the Cascades. New snow amounts this morning were about 8-12 inches at Mt Hood.

The Meadows patrol only ventured up to 6600 feet today due to stormy conditions where they found lee slopes and start zones loading and pockets of 6-10 inch wind slab triggered by ski cuts and explosives.

Snowpack problems at Mt Hood for the time being should be in the upper or surface layers. The mid and lower snowpack at Mt Hood consists of layers of stable consolidated rounded grains or melt forms and crusts from multiple warm periods this winter. The snowpack at low elevations at Mt Hood remains meager to non-existent.

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.