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Avalanche Forecast

Archived

Apr 7th, 2017–Apr 8th, 2017

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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Mt Hood.

The avalanche danger will increase with elevation on Saturday creating dangerous avalanche conditions above treeline. Careful snowpack evaluation and cautious routefinding will be essential.

Detailed Forecast

Greatly decreasing winds and showers with cooler temperatures should be seen on Saturday.

New wind slab may be found on various aspects above treeline due to the recent and latest strong and shifting winds. This avalanche problem may also creep down into the near treeline.

Loose wet avalanches at lower elevations may remain active on Saturday. Watch for wet surface snow deeper than a few inches, pinwheels and initial natural releases that indicate an increasing loose wet avalanche danger. Be wary of steep slopes with terrain traps such as cliffs or if heavily treed, where even a small loose wet avalanche could have big consequences.

Recent cornices are very large and have likely been weakened during this most recent storm cycle. 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.

Other avalanche problems not listed that may be encountered on Saturday include storm slab in more sheltered areas above treeline that experienced rapidly accumulating snowfall for more than a few hours.

Remember that solar effects can rapidly increase the touchiness of various type of avalanches at this time of year.

Snowpack Discussion

Weather and Snowpack

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

Fair but cool weather has been seen in the Olympics and Cascades Monday and Tuesday. Reports generally indicate strong surface or near surface crust layers and shallow recent snow. 

A stalled frontal boundary on Wednesday to Thursday morning brought heavy rain and snow to Mt Baker with light rain or snow for the rest of the Cascades. Snow levels were generally between 6500-7500 feet on Wednesday on Mt. Hood, lowering to 5500-6500 on Thursday. For the 3 days ending Friday morning NWAC stations at Mt Hood had about .8 inches of WE which will have fallen as snow above the snow levels.

A deep low pressure system moved north just off the Washington coast on Friday. Snow levels are running in the 4-5000 foot range on Friday. By Saturday morning 24 hour WE at NWAC stations at Mt Hood should be about another .75 inches of WE which will have fallen as snow above the rather low snow levels.

Recent Observations

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

On Thursday, the Meadows pro-patrol checked in reporting no recent avalanche concerns in their area.

On Friday NWAC pro-observer Laura Green was at Mt Hood Meadows and above treeline indicated a continuing 1 inch plus surface crust over wet snow. Wind transport had created 6-8 inch pocket of snow but she reported no avalanches and no signs of instability.

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.