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Avalanche Forecast

Archived

Mar 10th, 2016–Mar 11th, 2016

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

Wind slabs may still be lurking in the upper portion of the above treeline band on lee aspects. Loose wet avalanches seem unlikely except on steeper solar slopes near and below treeline if thin surface crusts soften early in the day. 

Detailed Forecast

Clouds should spread over Mt. Hood from the south Friday morning as moisture rotates northward and a weak frontal band offshore approaches. Light precipitation should develop mid-day, although new snow amounts look unimpressive through the daylight hours. Snow levels should remain moderate Friday, rising along with daytime warming. 

Wind slabs and cornices found in the upper reaches of the above treeline band should be less sensitive Friday but still capable of producing large avalanches in isolated areas.

Wind slabs may still be lurking in the upper portion of the above treeline band on lee aspects. Loose wet avalanches seem unlikely except on steeper solar slopes near and below treeline if thin surface crusts soften early in the day. Still, avoid terrain traps where even a small yet heavy loose wet avalanche would have serious consequences.

Snowpack Discussion

Weather and Snowpack

The nonstop active weather pattern continues to push a storm system through the PNW almost every day or two resulting in fluctuating snow levels and periods of very strong winds (100+ mph gusts have not been uncommon at the Mt Hood Meadows Cascade Express station).

A front Sunday and a cooler upper trough Monday brought some snow with 2 day storm totals of about 8-9 inches at Mt Hood ending Tuesday morning.

A strong storm arrived Wednesday morning bringing heavy snowfall/rain at rising temperatures and very strong S-SW ridgetop winds. About 1.5 inches of water accumulated at the Mt. Hood Meadows and Timberline stations through early Thursday morning, but unfortunately most of the precipitation ended up in liquid form. There are several crusts in the upper snowpack interspersed with moist or wet grains.

The mid and lower snow pack at Mt Hood should be a stable mix of crusts and layers of moist and rounded snow crystals.

Recent Observations

On Wednesday morning, new extensive wind slabs were forming on lee slopes near and above treeline. Explosive control performed by Mt. Hood Meadows pro-patrol Wednesday produced widespread slab releases on wind loaded N-NE facing terrain with crown depths of 2 feet common.  Storm slabs Wednesday morning changed to loose-wet avalanches by midday as temperatures rose and snow changed to rain below treeline. 

On Thursday, NWAC pro-observer Laura Green toured in the Mitchell and Heather drainages and found evidence of rain up to at least 6600 feet. Thin wind pockets were observed on lee slopes above treeline. A supportable rain crust did not make for good skiing, but on the plus side no avalanche problems were noted. Runnels were observed below 6000'. 

Problems

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.