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Avalanche Forecast

Archived

Mar 25th, 2015–Mar 26th, 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

Mt Hood.

Dangerous avalanche conditions are expected Thursday above treeline mainly due to loose wet avalanches that will have the ability to start in the surface layers and entrain snowfall received earlier this week. Stay conservative with your terrain selection Thursday. 

Detailed Forecast

Mostly sunny skies for Mt. Hood Thursday afternoon along with high freezing levels will maintain the threat of loose wet avalanches, especially on solar slopes near and above treeline that did not naturally avalanche Wednesday.

Loose wet avalanches starting above treeline Thursday may start in the surface layers and entrain snowfall received earlier this week. Larger avalanches will be possible above treeline where more recent snowfall has been received.  Avoid steeper slopes if you are sinking in more than a few inches, and be aware the even small loose wet avalanches are powerful and can push you into unintended terrain features.  

Fresh cornices along ridgelines have likely been weakened and should become susceptible to failure Thursday with warming and potential sunshine. Make sure to give them a wide berth, and be aware of corniced slopes above you. 

Lingering wind slab is possible above treeline on lee aspects especially above Wednesday's snow line.    

Less recent snow and ample terrain anchors may limit the avalanche danger below treeline. 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 building some stubborn wind slab up to 1 foot on lee NE slopes as noted my the Meadows pro patrol. 

A fairly vigorous low pressure system moved east over the Mt Hood area Monday night/Tuesday morning offering a taste of winter-like conditions; new snow amounts were about 9-11 inches at Mt Hood. On Tuesday, the Meadows patrol only ventured up to 6600 feet 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. Those same lee slopes at 6600 feet on Wednesday AM produced pockets on wind slab that did not readily propagate along with some sensitive cornices.

Light to moderate precipitation along with a warming trend tapered off Wednesday afternoon as snow levels pushed above 7000 feet. 

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

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.

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.