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Avalanche Forecast

Archived

Feb 25th, 2016–Feb 26th, 2016

Alpine
Natural avalanches unlikely, human triggered possible.
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

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Earlier formed wind slabs should continue to stabilize, but remain aware of these potentially touchy wind slabs on a variety of aspects, most likely those facing westerly. Strong late winter sunshine and mild temperatures should cause possible loose wet avalanches on steeper solar slopes in your area. 

Detailed Forecast

Increasing high clouds overnight Thursday should still allow for stabilizing surface crust formation by early Friday.

A weak front should allow for light rain and snow at moderate freezing levels later Friday afternoon. Only a light amount of precipitation is expected during the daylight hours and this should not cause a significant increase in the danger.  

Some shallow new wind slabs may form at higher elevations by late Friday on some lee slopes that receive greater precipitation.

Snowpack Discussion

Weather and Snowpack

Dry weather with the warmest temperatures of the winter occurred February 7-10th with temperatures climbing into the 50's in most areas east of the crest. Snow in the northeast zone buried the crust with about 2-3 feet of snowfall starting February 11th through Saturday morning February 20th.

Rain and mild temperatures were seen in the central east and southeast zones last week forming a newer crust further south and outside the Washington Pass zone. An active and cooler pattern buried the crust in the central and southeast zones starting February 17th with about 6-10 inches of snow in the near and above treeline Wednesday through Saturday morning.

Up to a few inches of additional snowfall fell by Monday morning. Dry, cool conditions Tuesday and mild temperatures Wednesday have allowed for continued settlement and stabilization of any recent wind slab layers. 

The past two days have seen sunshine and very mild temperatures, rising into the 40's or 50's. This fair and mild weather has allowed for melt-freeze crust formation overnight and varying amounts of wet surface snow depending on aspect, during the warmest part of the day and helped to stabilize earlier formed wind slabs. 

Recent Observations

NWAC pro-observer Jeff Ward in the Northeast Washington Cascades Wednesday, reported recent wind slabs were becoming more stubborn and isolated near and above treeline, while large softening cornices were seen as the greatest avalanche concern. 

Tom Curtis was in the Icicle Creek drainage Tuesday and observed light to moderate wind transport near and above treeline. Below treeline, the most recent storm snow was unconsolidated and poorly bonded to the most recent crust. 

 

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.

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.

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.