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Avalanche Forecast

Archived

Apr 8th, 2015–Apr 9th, 2015

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

Mt Hood.

The main avalanche problem at Mt Hood should be possible small loose wet avalanches on solar slopes. But isolated storm slab may still be found on slopes mainly above treeline where there has been recent heavier snow showers.

Detailed Forecast

The weak shortwave, moisture and instability should continue to linger over Washington on Thursday. So expect cumulus and a slight chance of showers will be forecast again Thursday afternoon mainly over the central and south Cascades.

It's April, so be aware of the increased sun effects reaching more aspects and affecting the snow surface fairly quickly. Loose wet avalanches involving shallow amounts of recent storm snow will be possible Thursday, especially in any direct sun on solar slopes.

Most storm slab should be stabilized by Thursday. But continue to watch for storm slab layers where storm snow instabilities may have formed during snow showers or where recent snow seems poorly bonded to underlying crusts.

Cornices won't be highlighted as an avalanche problem due to the cool weather but use caution on slopes below cornices and on ridges where it can be hard to know if a cornice is present.

Snowpack Discussion

A front caused moderate west winds and 1-3 inches of new snow at NWAC stations on Mt. Hood Friday night, with some moderate westerly wind transport above treeline. But the Meadows patrol reported only isolated pockets of wind slab up to 1 foot above treeline on lee aspects over the weekend.

A large weak upper trough moved over the Northwest last weekend through early this week. The main showers at Mt Hood were Sunday when NWAC stations at Mt Hood had 6-7 inches. Freezing levels have been very low in April compared to most of the winter, averaging about 4-5000 feet. Shallow 4 inch potential storm slab layers was reported by the Meadows patrol Monday.

A weak shortwave, moisture and instability is causing cumulus and showers Wednesday mainly over the central and south Cascades. The Meadows patrol reports easy shears in quick test pits in recent snow at 7300 feet on Wednesday.

Snowpack problems at Mt Hood should remain 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 season. Many areas at low elevations do not have enough snow to cause an avalanche danger.

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.

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.