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Avalanche Forecast

Archived

Jan 27th, 2016–Jan 28th, 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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Olympics.

In the Olympics the main problem should continue to be loose-wet avalanches on Thursday. Watch for wet surface snow deeper than a few inches and pinwheels or roller balls that usually precede loose wet avalanches.

Detailed Forecast

Periods of moderate to heavy rain overnight Wednesday and early Thursday will cause further wet snow conditions, including increasing the likelihood of loose-wet avalanches on steep slopes.

In the Olympics the main problem should continue to be loose wet avalanches Thursday. Watch for wet surface snow deeper than a few inches and pinwheels or roller balls that usually precede loose wet avalanches. This may be more likely on non solar slopes holding loose snow, but will be indicated on all aspects. 

Previous wind slab in the above treeline may be loaded and weakened by wet surface snow. This avalanche problem may be getting unlikely, but watch for signs of previous firmer transported snow mainly on northwest to southeast aspects.

Cooling and rain turning to snow showers is expected later Thursday. This should allow for a good bond to develop between the previously wet surface snow and new snow. Only light snow showers are expected later Thursday, with shallow new snow amounts expected. This should allow for a newly forming crust to begin stabilizing the snowpack. 

Snowpack Discussion

A warm front last Thursday caused heavy rain in the Olympics and this caused a loose wet avalanche cycle on steep slopes in all the elevation bands.

This was followed by cooler weather and shallow new snow. The cooling formed good bonding to the forming crust as observed by NWAC pro-observer Matt Schonwald Friday.

Matt reported generally stable surface snow conditions with no layers of concern in the BTL and NTL elevation zones. Overall the snowpack consisted of a few inches of saturated snow, well bonded to supportive dryer, old snow and a newly forming crust. Stability tests were all negative. Some transport of loose surface snow was seen being deposited on the northerly facing terrain below ridges, but no distinctive wind slab had formed as of Friday afternoon.

A strong front, moving into the Olympics Wednesday afternoon, is bringing increasing rain at high freezing levels. This is wetting and saturating surface snow layers, increasing wet snow conditions. 

 

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.

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.