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Avalanche Forecast

Archived

Apr 15th, 2017–Apr 16th, 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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

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Sunny warmer weather will be the main factor on Sunday. You will need to be able to judge the potential for loose wet avalanches. Give cornices a wide berth when traveling on or below ridges.

Detailed Forecast

Sunny, warmer weather with mostly S-SE-E crest level winds should be seen on Sunday.

A central question will be the extent loose wet avalanches on Sunday. Surface crusts from over night cooling should break fairly fast on Sunday and sunny weather can quickly activate loose wet avalanches. Loose wet avalanches will be indicated on all aspects but will be most likely on solar slopes. Watch for wet surface snow deeper than a few inches and initial small loose wet avalanches that indicate an increasing danger. Remember that even slow moving loose wet avalanches are powerful and you don't want to get caught in one especially above a terrain trap. Even small loose wet avalanches can have serious consequences.

Recent cornices are very large and resulting slab avalanches are dangerous and unpredictable. There have been numerous recent cornice failures with some being very large in the Washington Cascades. Five people were tragically killed by a cornice release in British Columbia on Saturday. Give cornices a wide berth if traveling along ridge-lines and avoid slopes below cornices. Many current back country routes are exposed to cornices; don't linger below one. See a blog post regarding cornices here.

Warmer daytime temperatures are probably helping stabilize recently formed wind slab. Wind slab is mostly likely to linger on NW-SE slopes and will probably be stubborn to release by Sunday. Watch for firmer wind transported snow that indicates the presence of wind slab. 

 

Snowpack Discussion

Weather and Snowpack

Warmer temperatures with periods of rain received in mid March has left behind a well consolidated snowpack with one or more strong melt freeze crusts in the upper portion of the snowpack in the near and below treeline elevation bands. 

A series of strong spring storms occurred during the first week of April.

A persistent, large upper trough was over the Northwest coastal waters the past few days causing snow and cool temperatures for this time of year. New snow each of the past 3 days east of the Cascade crest was probably up to a couple or a few inches at higher elevations.

Recent Observations

North

No recent observations.

Central

NWAC's Tom Curtis was on Irving Peak near Poe Mountain, NE of Lake Wenatchee on Wednesday, 4/12. There was about 6-8 inches of recent storm snow over the most recent melt-freeze crust on shaded slopes. This snow became moist to wet through the day and with little effort produced rather large loose-wet avalanches, even on steeper N-NE aspects. Several large to very large loose wet slides were observed and heard across the valley, releasing on N-NE facing terrain on Nason Ridge, including higher above treeline. Cornices were also very large. These conditions limited any travel on steep terrain of consequence.

South

No recent observations.

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.

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.