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Avalanche Forecast

Archived

Apr 2nd, 2017–Apr 3rd, 2017

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.

Avoid steep sun exposed terrain if you see wet snow deeper than a few inches and initial rollerballs or small loose wet avalanches that can indicate an increasing loose wet avalanche danger. Avoid travel on or below cornices.

Detailed Forecast

Light winds and sunny weather should be seen on Monday with moderately warmer temperatures.

Sunshine will melt and possibly cause loose wet snow avalanches on steep solar slopes. Avoid steep sun exposed terrain if you see wet snow deeper than a few inches and initial rollerballs or small loose wet avalanches that can indicate an increasing loose wet avalanche danger.

Recent cornices are very large. Natural cornice releases and resulting slab avalanches are dangerous and unpredictable. Give cornices a wide berth if traveling along ridge-lines and avoid slopes below large cornices. See a blog post regarding cornices here.

 

Snowpack Discussion

Weather and Snowpack

March was wet and wild for weather and avalanches in the Cascades. 

The last major system in March was seen Tuesday and Wednesday when a strong low pressure system brought rising snow levels and locally heavy precipitation along the west slopes of the Cascades including Mt. Hood. After receiving a few inches of snow Tuesday night, Mt. Hood saw periods of moderate to heavy rain to above 7000 feet on Wednesday.

Cooling and showery weather Thursday allowed wet snow to begin refreezing with 2-5 inches of new snow at NWAC stations at Mt Hood. The winds diminished Thursday and combined with daytime warming, this allowed for wind slab and storm slab to begin stabilizing.

Very mild temperatures and increased solar radiation Friday allowed for wet surface snow conditions in most terrain, even northerly facing slopes. Shallow loose-wet snow avalanches occurred Friday on many steep slopes but remained small, along with snowpack consolidation.

A weak front crossed the Northwest on Saturday morning causing light rain mainly along the Cascade west slopes. This was followed by an upper trough on that caused some light amounts of snow along the Cascade west slopes at much cooler temperatures on Sunday. In most areas this will have refrozen upper layers of the snowpack.

Recent Observations

The storm limited observations on Wednesday, but rain quickly penetrated the upper snowpack in the Mt. Hood Meadows base area by late morning. 

NWAC pro-observer Laura Green was in the White River area in the 4500-6000 ft range on Friday and reported 4-13 cm of recent snow on the P crust from mid week. Pit tests gave hard results that did not indicate propagation on a layer at 30 cm. She noted natural wind slab releases in the above treeline and loose wet avalanches below from Thursday.

The Meadows pro-patrol on Saturday and Sunday reported triggered loose wet avalanches becoming possible on solar slopes. Otherwise the recent crust is the predominate snow surface there with small shallow areas of wind transported snow been soaked by rain and frozen in place.

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.