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Avalanche Forecast

Archived

Mar 21st, 2016–Mar 22nd, 2016

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.

A mix of spring avalanche problems exists with no one problem dominating. Evaluate the local snow and terrain carefully on Monday.

Detailed Forecast

Light to moderate west winds and several inches of new snow should be seen in the near and above treeline zone along the west slopes Monday night and Tuesday. Temperatures should continue to slightly cool from the previous couple days.

This weather may build new wind slab on lee slopes in the near and above treeline through the day light hours on Tuesday. This is most likely on N-SE slopes. Firm wind transported snow and snowpack cracking can be good signs of wind slab layers.

Continued wet snow conditions can't be ruled out on Tuesday. The cooler temperatures should limit this problem to the below treeline. Watch for wet snow deeper than a few inches and pinwheels or natural releases.

Recently formed cornices have grown large and can become sensitive following nights with above freezing temperatures.  Avoid areas on ridges or summits where there may be a cornice and avoid slopes below cornices. Cooler temperatures Tuesday may help to temporarily strengthen cornices Tuesday.

Snowpack Discussion

Weather and Snowpack

A combination of sun and mild temperatures for several days gave way to warm temperatures and light rain Sunday 3/20. This weather caused the 4 feet of storm snow that accumulated at Mt Hood from about March 9-15 to settle, consolidate and stabilize. Recent sun, warmth, freezing and rain drastically changed snow conditions. Surface snow conditions have become highly variable, ranging from some well settled old snow on steep shaded slopes and a mix of surface crusts, wind buffed surfaces or shallow wet snow on other aspects.

Earlier avalanche problems of wind and storm slab have settled and stabilized over the past several days of mild weather. Sites on Mt Hood have seen the snowpack settle 10-15 inches over the past five days, since the strong storms ended March 15th.

A period of strong east winds near the Cascade crest Thursday and Friday 3/17-18 transported available loose surface snow onto many exposed westerly facing slopes, building new wind slab layers as of Friday. These slabs should have strengthened and stabilized. 

Moderate to somewhat strong southwest winds were seen Sunday night and up to a few inches of snow was seen at higher elevations ending Monday morning. Some new, small shallow wind slab might be possible above treeline.

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

Recent Observations

A report from the Mt Hood Meadows pro-patrol on Monday 3/21 indicated pockets of new wind deposited snow in the above and near treeline. Ski cuts gave no results and most surfaces were still melt freeze snow. A breakable crust over wet snow was reported below treeline.

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.

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.